Notes on the Troubleshooting and Repair of Computer and Video Monitors

Introduction

Monitors, monitors, and more monitors

In the early days of small computers, a 110 baud teletype with a personal
paper tape reader was the ‘preferred’ input-output device (meaning that
this was a great improvement over punched cards and having to deal with
the bozos in the computer room. Small here, also meant something that
would comfortably fit into a couple of 6 foot electronics racks!)

The earliest personal computers didn’t come with a display – you connected
them to the family TV. You and your kids shared the single TV and the
Flintstones often won out. The Commodore 64 would never have been as
successful as it was if an expensive monitor were required rather than
an option.

However, as computer performance improved, it quickly became clear that
a dedicated display was essential. Even for simple text, a TV can only
display 40 characters across the screen with any degree of clarity.

When the IBM PC was introduced, it came with a nice 80×25 green monochrome
text display. It was bright, crisp, and stable. Mono graphics (MGA or MDA)
was added at 720×350, CGA at a range of resolutions from 160×200 to 640×200
at 2 to 16 colors, and EGA extended this up to a spectacular resolution of
640×350. This was really fine until the introduction of Windows (well, at
least once Windows stayed up long enough for you to care).

All of these displays used digital video – TTL signals which coded for a
specific discrete number of possible colors and intensities. Both the video
adapter and the monitor were limited to 2, 4, 16, or a whopping 64 colors
depending on the graphics standard. The video signals were logic bits – 0s
and 1s.

With the introduction of the VGA standard, personal computer graphics
became ‘real’. VGA and its successors – PGA, XGA, and all of the SVGA
(non) standards use analog video – each of the R, G, and B signals is
a continuous voltage which can represent a continuous range of intensities
for each color. In principle, an analog monitor is capable of an unlimited
number of possible colors and intensities. (In practice, unavoidable noise
and limitations of the CRT restricts the actual number to order of 64-256
distinguishable intensities for each channel.)

Note that analog video was only new to the PC world. TVs and other video
equipment, workstations, and image analysis systems had utilized analog
signals for many years prior to the PC’s ‘discovery’ of this approach. In
all fairness, both the display adapter and monitor are more expensive so
it is not surprising that early PCs did not use analog video.

Most of the information in this document applies to color computer video
monitors and TV studio monitors as well as the display portions of television
sets. Black and white, gray scale, and monochrome monitors use a subset
of the circuitry (and generally at lower power levels) in color monitors so
much of it applies to these as well.

For most descriptions of symptoms, testing, diagnosis, and repair, an
auto-scan PC SVGA monitor is assumed. For a fixed frequency workstation
monitor, studio video monitor, or closed circuit TV monitor, only a subset
of the possible faults and procedures will apply.

Note: we use the term ‘auto-scan’ to describe a monitor which accepts a wide
(and possibly continuous) range of scan rates. Usually, this refers mostly
to the horizontal frequency as the vertical refresh rate is quite flexible on
many monitors of all types. Fixed scan or fixed frequency monitors are
designed to work with a single scan rate (though a 5% or so variation may
actually be accepted). Multi-scan monitors sync at two or more distinct
scan rates. While not very common anymore, multi-scan monitors may still
be found in some specific applications.

Related Information

See the documentss:
Troubleshooting and Repair of Small Switchmode Power
Supplies and
Troubleshooting and Repair of Television Sets for additional
useful pointers. Since a monitor must perform a subset of the functions
of a TV, many of the problems and solutions are similar. For power related
problems the info on SMPSs may be useful as well. If you are considering
purchasing a monitor or have one that you would like to evaluate, see
the companion document: Performance Testing of
Computer and Video Monitors.

Monitor fundamentals

Note: throughout this document, we use the term ‘raster’ to refer to the
entire extent of the scanned portion of the screen and the terms ‘picture’,
‘image’. or ‘display’, to refer to the actual presentation content.

Monitors designed for PCs, workstations, and studio video have many
characteristics in common. Modern computer monitors share many
similarities with TVs but the auto-scan and high scan rate deflection
circuitry and more sophisticated power supplies complicates their servicing.

Currently, most inexpensive computer monitors are still based on the Cathode
Ray Tube (CRT) as the display device. However, handheld equipment,
laptop computers, and the screens inside video projectors now use flat
panel technology, mostly Liquid Crystal Displays – LCDs. These are
a lot less bulky than CRTs, use less power, and have better geometry – but
suffer from certain flaws. As the price of LCD (and other technology) flat
screen technology decreases, such monitors will become dominant for desktop
computers as well and CRT based monitors will eventually go the way of
dinosaurs, core memory, and long playing records that dominated their
respective industries for decades but eventually yielded to fundamentally new
technology. 🙂

However, there are still problems with (low cost, at least) LCD monitors.
First, the picture quality in terms of gray scale and color is generally
inferior to a decent analog monitor. The number of distinct shades of
gray or distinct colors is a lot more limited. They are generally not as
responsive as CRTs when it comes to real-time video which is becoming
increasingly important with multimedia computers. This is partly due to
the response of the LCD material itself but also a result of the scan
conversion that’s needed for non-native resolution formats. Brightness
is generally not as good as a decent CRT display. And last but not least,
the cost is still somewhat higher due both to the increased complexity of flat
panel technology and lower production volumes (though this is certainly
increasing dramatically). It is really hard to beat the simplicity of the
shadow mask CRT.

The really bad news from the perspective of repair is that they generally
cannot be repaired outside of a manufacturer authorized service center and
the way they do the repair most likely will be to swap the entire LCD/driver
panel, if not the entire monitor. Only repair of the most simple problems
like obvious bad connections, a bad cable, a bad backlight lamp, or a failure
of the power supply or backlight inverter, can realistically be accomplished
without fancy specialized test equipment and facilities. Access to the
backlight lamps might substantial disassembly.

Buying a broken LCD monitor to repair may have better odds than the
State Lottery, but probably not by much. Where one or more columns or
rows or an entire half screen are not displaying properly, I wouldn’t
consider it unless nearly totally free, hoping for a miracle, and even then it
might not be worth it. Loose connectors and solder joints are possible,
though not nearly as common as with CRT monitors.

Also a note to those with less than perfect vision: If you tend to view your
monitor from less than 10 to 15 inches, you may be disappointed, or at least
have a hard time getting used to LCD monitors. The appearance of a CRT
display is nearly independent of viewing angle. But for an LCD display,
this is not the case. Only the central part of your field of vision will have
the proper brightness, contrast, and color rendition. If
the curser isn’t within this central area, it will be harder to locate than
on a CRT. In short, don’t just depend on the hype. An LCD with a slightly
lower contrast ratio and lower price may have a substantially wider viewing
angle and better match to your needs than a top-of-the-line model. Test
drive multiple LCD monitors before committing to one!

Nonetheless, a variety of technologies are currently competing for use in
the flat panel displays of the future. Among these are advanced LCD,
plasma discharge, and field emission displays. Only time will tell which, if
any survives to become **the** picture-on-the-wall or notepad display – at
reasonable cost.

Projection displays, on the other hand, can take advantage of a novel
development in integrated micromachining – the Texas Instruments Inc.
Digital Micromirror Device (DMD). This is basically
an integrated circuit with a tiltable micromirror for each pixel fabricated
on top of a static memory – RAM – cell. DMD technology would
permit nearly any size projection display to be produced and would
therefore be applicable to HDTV as well as PCs. Since it is a reflective
device, the light source can be as bright as needed. This technology is
already appearing in commercial high performance computer projectors and
is competing for use in totally digital movie theaters to replace the film
projector, but to my knowledge is not in any consumer TV sets – yet.

As noted, the plasma panel flat screen display has been around for several
years in high-end TVs, typically in the 42 inch diagonal range. But
they are very expensive ($5,000 to $15,000 as of Winter, 2003), and their
life expectancy may be limited due to the gradual degradation of the active
pixel cells – which occurs faster than for a CRT. The physical resolution
is also probably still too low to really justify the large screen size for
computer displays. However, there is little doubt that this or a similar
technology will eventually replace the direct view CRT and 3-tube projection
TVs in the mid to large screen sizes in the not too distant future. But to
what extent it is used for computer monitors is still unclear.

The remainder of this document concentrates on CRT based computer and video
monitors since these still dominate the market and realistically, they are
the only type where there is a good chance of repair without access to
specialized test equipment and parts. I wouldn’t recommend any sort of
attempt at repair of flat screen TVs or monitors – no matter what the size –
beyond checking for bad connections, dead power supplies, or other obvious
problems. The chance of success is vanishingly small and it’s very likely
that even with great care, damage could occur to the panels or circuitry.

Monitor characteristics

The following describe the capabilities which characterize a display:

1. Resolution – the number of resolvable pixels on each line and the
   number of scanning lines. Bandwidth of the video source, cable, and
   monitor video amplifiers as well as CRT focus spot size are all critical.
   However, maximum resolution on a color CRT is limited by the dot/slot/line
   pitch of the CRT shadow/slot mask or aperture grille.
2. Refresh rate – the number of complete images ‘painted’ on the screen
   each second. Non-interlaced or progressive scanning posts the entire
   frame during each sweep from top to bottom. Interlaced scanning posts
   1/2 of the frame called a field – first the even field and then the
   odd field. This interleaving reduces the apparent flicker for a given
   display bandwidth when displaying smooth imagery such as for TV. It is
   usually not acceptable for computer graphics, however, as thin horizontal
   lines tend to flicker at 1/2 the vertical scan rate. Refresh rate is the
   predominant factor that affects the flicker of the display though the
   persistence of the CRT phosphors are also a consideration. Long persistence
   phosphors decrease flicker at the expense of smearing when the picture
   changes or moves. Vertical scan rate is equal to the refresh rate for
   non-interlaced monitors but is the twice the refresh rate for interlaced
   monitors (1 frame equals 2 fields). Non-interlaced vertical refresh rates
   of 70-75 Hz are considered desirable for computer displays. Television
   uses 25 or 30 Hz (frame rate) interlaced scanning in most countries.
3. Horizontal scan rate – the frequency at which the electron beam(s) move
   across the screen. The horizontal scan rate is often the limiting factor
   in supporting high refresh rate high resolution displays. It is what may
   cause failure if scan rate speed limits are exceeded due to the component
   stress levels in high performance deflection systems.
4. Color or monochrome – a color monitor has a CRT with three electron
   guns each associated with a primary color – red, green, or blue.
   Nearly all visible colors can be created from a mix of primaries
   with suitable spectral characteristics using this additive color
   system.

   A monochrome monitor has a CRT with a single electron gun. However,
   the actual color of the display may be white, amber, green, or whatever
   single color is desired as determined by the phosphor of the CRT selected.

5. Digital or analog signal – a digital input can only assume a discrete
   number of states depending on how many bits are provided. A single bit
   input can only produce two levels – usually black or white (or amber,
   green, etc.). Four bit EGA can display up to 16 colors (with a color
   monitor) or 16 shades of gray (with a monochrome monitor).

   Analog inputs allow for a theoretically unlimited number of possible gray
   levels or colors. However, the actual storage and digital-to-analog
   convertors in any display adapter or frame store and/or unavoidable
   noise and other characteristics of the CRT – and ultimately, limitations
   in the psychovisual eye-brain system will limit this to a practical
   maximum of 64-256 discernible levels for a gray scale display or for
   each color channel.

   However, very high performance digital video sources may have RAMDACs (D/A
   convertors with video lookup tables) of up to 10 or more bits of intensity
   resolution. While it is not possible to perceive this many distinct gray
   levels or colors (per color channel), this does permit more accurate tone
   scale (‘gamma’) correction to be applied (via a lookup table in the RAMDAC)
   to compensate for the unavoidable non-linearity of the CRT phosphor
   response curve or to match specific photometric requirements.

Types of monitors

Monitors can be classified into three general categories:

1. Studio video monitors – Fixed scanning rate for the TV standards
   in the country in which they are used. High quality, often high
   cost, utilitarian case (read: ugly), underscan option. Small
   closed circuit TV monitors fall into the class. Input is usually
   composite (i.e., NTSC or PAL) although RGB types are available.
2. Fixed frequency RGB – High resolution, fixed scan rate. High quality,
   high cost, very stable display. Inputs are analog RGB using either
   separate BNC connectors or a 13W3 (Sun) connector. These often have
   multiple sync options. The BNC variety permit multiple monitors to
   be driven off of the same source by daisychaining. Generally used
   underscanned for computer workstation (e.g., X-windows) applications
   so that entire frame buffer is visible. There are also fixed frequency
   monochrome monitors which may be digital or analog input using a BNC,
   13W3, or special connector.
3. Multi-scan or auto-scan – Support multiple resolutions and scan rates
   or multiple ranges of resolutions and scan rates. The quality and
   cost of these monitors ranges all over the map. While cost is not
   a strict measure of picture quality and reliability, there is a
   strong correlation. Input is most often analog RGB but some older
   monitors of this type (e.g., Mitsubishi AUM1381) support a variety
   of digital (TTL) modes as well. A full complement of user controls
   permits adjustment of brightness, contrast, position, size, etc. to
   taste. Circuitry in the monitor identifies the video scan rate
   automatically and sets up the appropriate circuitry. With more
   sophisticated (and expensive) designs, the monitor automatically
   sets the appropriate parameters for user preferences from memory as well.
   The DB15 high density VGA connector is most common though BNCs may be
   used or may be present as an auxiliary (and better quality) input.

Why auto-scan?

Thank IBM. Since the PC has evolved over a period of 15 years, display
adapters have changed and improved a number of times. With an open system,
vendors with more vision (and willing to take more risks) than IBM were
continuously coming up with improved higher resolution display adapters.
With workstations and the Apple MacIntosh, the primary vendor can control
most aspects of the hardware and software of the computer system. Not so
with PCs. New improved hardware adapters were being introduced regularly
which were not following any standards for the high resolution modes (but
attempted to be backward compatible with the original VGA as well as EGA
and CGA (at least in terms of software).) Vast numbers of programs were
written that were designed to directly control the CGA, EGA, and VGA
hardware. Adapter cards could be designed to emulate these older
modes on a fixed frequency high resolution monitor (and these exist to
permit high quality fixed scan rate workstation monitors to be used on PCs)
However, these would be (and are) much more expensive than basic display
adapters that simply switch scan rates based on mode. Thus, auto-scan
monitors evolved to accommodate the multiple resolutions that different
programs required.

Note: The generic term ‘auto-scan’ is used to refer to a monitor which
automatically senses the input video scan rate and selects the appropriate
horizontal and vertical deflection circuitry and power supply voltages to
display this video. Multi-scan monitors, while simpler than true auto-scan
monitors, will still have much of the same scan rate detection and selection
circuitry. Manufacturers use various buzz words to describe their versions
of these monitors including ‘multisync’, ‘autosync’,’panasync’, ‘omnisync’,
as well as ‘autoscan’ and ‘multiscan’.

Ultimately, the fixed scan rate monitor may reappear for PCs. Consider
one simple fact: it is becoming cheaper to design and manufacture complex
digital processing hardware than to produce the reliable high quality
analog and power electronics needed for an auto-scan monitor. This is
being done in the specialty market now. Eventually, the development
of accelerated chipsets for graphics mode emulation may be forced by
the increasing popularity of flat panel displays – which are basically
similar to fixed scan rate monitors in terms of their interfacing
requirements.

Analog versus digital monitors

There are two aspects of monitor design that can be described in terms
of analog or digital characteristics:

1. The video inputs. Early PC monitors, video display terminal
   monitors, and mono workstation monitors use digital input signals
   which are usually TTL but some very high resolution monitors may
   use ECL instead.
2. The monitor control and user interface. Originally, monitors all
   used knobs – sometimes quite a number of them – to control all
   functions like brightness, contrast, position, size, linearity,
   pincushion, convergence, etc. However, as the costs of digital
   circuitry came down – and the need to remember settings for multiple
   scan rates and resolutions arose, digital – microprocessor
   control – became an attractive alternative in terms of design,
   manufacturing costs, and user convenience. Now, most better quality
   monitors use digital controls – buttons and menus – for almost all
   adjustments except possibly brightness and contrast where knobs are
   still more convenient.

Since monitors with digital signal inputs are almost extinct today except for
specialized applications, it is usually safe to assume that ‘digital’ monitor
refers to the user interface and microprocessor control. And, except perhaps
for the very cheapest monitors, all now have digital controls.

Interlacing

Whether a monitor runs interlaced or non-interlaced is almost always
strictly a function of the video source timing. The vertical sync
pulse is offset an amount equal to 1/2 the line time on alternate fields
(vertical scans – two fields make up a frame when interlaced scanning is
used).

• Generally, a monitor that runs at a given resolution non-interlaced can run
  interlaced at a resolution with the same number of pixels per line but twice
  the number of lines vertically at roughly the same horizontal and vertical
  scan rates and video bandwidth (but half the frame rate).
• Alternatively, it may be possible to increase the resolution in both
  directions while keeping the horizontal scan rate the same thus permitting a
  monitor to display the next larger size format. However, in this case, the
  video bandwidth will increase.

Here are a couple of examples:

• A monitor that will run 640×240 at 60 frames per second non-interlaced will
  run 640×480 at 30 frames per second interlaced. This would permit a monitor
  with a horizontal scan rate of 15.7 kHz (NTSC TV compatible) to display VGA
  resolution images – though they will likely flicker since the 30 Hz is way
  too low for most graphics.
• A resolution of 1024×768 at 50 frames per second interlaced requires
  roughly the same horizontal scan rate (about 42 kHz) as 800×600 at 66 frames
  per second non-interlaced. The flicker may be acceptable in this case being
  at 50 Hz for the worst case of single horizontal lines as the high 100 Hz
  vertical scan rate will reduce flicker otherwise.

Whether the image is usable at the higher resolution of course depends on many
other factors (in addition to flicker) including the dot pitch of the CRT and
video bandwidth of the video card and monitor video amplifiers, as well as
cable quality and termination.

Monitor performance

The ultimate perceived quality of your display is influenced by many aspects
of the total video source/computer-cable-monitor system. Among them are:

1. Resolution of the video source. For a computer display, this is determined
   by the number of pixels on each visible scan line and the number of visible
   scan lines on the entire picture.
2. The pitch of the shadow mask or aperture grille of the CRT. The smallest
   color element on the face of the CRT is determined by the spacing of the
   groups of R, G, and B colors phosphors. The actual conversion from
   dot or line pitch to resolution differs slightly among dot or slot mask
   and aperture grille CRTs but in general, the finer, the better – and
   more expensive.

   Typical television CRTs are rather coarse – .75 mm might be a reasonable
   specification for a 20 inch set. High resolution computer monitors
   may have dot pitches as small as .22 mm for a similar size screen.

   A rough indication of the maximum possible resolution of the CRT can be
   found by determining how many complete phosphor dot groups can fit across
   the visible part of the screen.

   Running at too high a resolution for a given CRT may result in Moire – an
   interference pattern that will manifest itself as contour lines in smooth
   bright areas of the picture. However, many factors influence to what
   extent this may be a problem. See the section:
   Contour lines on high resolution monitors – Moire.

3. Bandwidth of the video source or display card – use of high performance
   video amplifiers or digital to analog convertors.
4. Signal quality of the video source or display card – properly designed
   circuitry with adequate power supply filtering and high quality components.
5. High quality cables with correct termination and of minimal acceptable
   length without extensions or switch boxes unless designed specifically
   for high bandwidth video.
6. Sharpness of focus – even if the CRT dot pitch is very fine, a fuzzy
   scanning beam will result in a poor quality picture.
7. Stability of the monitor electronics – well regulated power supplies
   and low noise shielded electronics contribute to a rock solid image.

The following are only partly dependent on the monitor’s design:

8. Anti-glare treatment of screen and ambient lighting conditions – No matter
   how good are the monitor’s electronics, the display can still be washed out
   and difficult or tiring to view if there is annoying glare or reflections.
   The lighting and location are probably more important than how the screen
   itself is designed to minimize glare.
9. Electromagnetic interference – Proximity to sources of magnetic fields and
   power line noise can degrade the performance of any monitor, no matter how
   well shielded it might be.

Performance testing of monitors

WARNING: No monitor is perfect. Running comprehensive tests on your
monitor or one you are considering may make you aware of deficiencies you
never realized were even possible. You may never be happy with any monitor
for the rest of your life!

Note: The intent of these tests is **not** to evaluate or calibrate a monitor
for photometric accuracy. Rather they are for functional testing of the
monitor’s performance.

Obviously, the ideal situation is to be able to perform these sorts of
tests before purchase. With a small customer oriented store, this may
be possible. However, the best that can be done when ordering by mail
is to examine a similar model in a store for gross characteristics and
then do a thorough test when your monitor arrives. The following should
be evaluated:

• Screen size and general appearance.
• Brightness and screen uniformity, purity and color saturation.
• Stability.
• Convergence.
• Edge geometry.
• Linearity.
• Tilt.
• Size and position control range.
• Ghosting or trailing streaks.
• Sharpness.
• Moire.
• Scan rate switching.
• Acoustic noise.

The companion document: Performance Testing of Computer
and Video Monitors provides detailed procedures for the evaluation of each
of these criteria.

CAUTION: Since there is no risk free way of evaluating the actual scan
rate limits of a monitor, this is not an objective of these tests. It
is assumed that the specifications of both the video source/card and the
monitor are known and that supported scan rates are not exceeded. Some
monitors will operate perfectly happily at well beyond the specified range,
will shut down without damage, or will display an error message. Others will
simply blow up instantly and require expensive repairs.

Monitor repair

Unlike PC system boards where any disasters are likely to only affect
your pocketbook, monitors can be very dangerous. Read, understand, and
follow the set of safety guidelines provided later in this document
whenever working on TVs, monitors, or other similar high voltage equipment.

If you do go inside, beware: line voltage (on large caps) and high voltage
(on CRT) for long after the plug is pulled. There is the added danger of
CRT implosion for carelessly dropped tools and often sharp sheetmetal
shields which can injure if you should have a reflex reaction upon touching
something you should not touch. In inside of a TV or monitor is no place
for the careless or naive.

Having said that, a basic knowledge of how a monitor works and what can
go wrong can be of great value even if you do not attempt the repair yourself.
It will enable you to intelligently deal with the service technician. You
will be more likely to be able to recognize if you are being taken for a ride
by a dishonest or just plain incompetent repair center. For example, a
faulty picture tube CANNOT be the cause of a color monitor only displaying
in black-and-white (this is probably a software or compatibility problem).
The majority of consumers – and computer professionals – may not know even
this simple fact.

This document will provide you with the knowledge to deal with a large
percentage of the problems you are likely to encounter with your monitors.
It will enable you to diagnose problems and in many cases, correct them
as well. With minor exceptions, specific manufacturers and models
will not be covered as there are so many variations that such a treatment would
require a huge and very detailed text. Rather, the most common problems
will be addressed and enough basic principles of operation will be provided
to enable you to narrow the problem down and likely determine a course of
action for repair. In many cases, you will be able to do what is required
for a fraction of the cost that would be charged by a repair center.

Should you still not be able to find a solution, you will have learned a great
deal and be able to ask appropriate questions and supply relevant information
if you decide to post to sci.electronics.repair. It will also be easier to do
further research using a repair text such as the ones listed at the end of
this document. In any case, you will have the satisfaction of knowing you
did as much as you could before taking it in for professional repair.
With your new-found knowledge, you will have the upper hand and will not
easily be snowed by a dishonest or incompetent technician.

Most Common Problems

The following probably account for 95% or more of the common monitor ailments:

• Intermittent changes in color, brightness, size, or position – bad
  connections inside the monitor or at the cable connection to the computer
  or or video source.
• Ghosts, shadows, or streaks adjacent to vertical edges in the picture –
  problems with input signal termination including use of cable extensions,
  excessively long cables, cheap or improperly made video cables, improper
  daisychaining of monitors, or problems in the video source or monitor
  circuitry.
• Magnetization of CRT causing color blotches or other color or distortion
  problems – locate and eliminate sources of magnetic fields if relevant
  and degauss the CRT.
• Electromagnetic Interference (EMI) – nearby equipment (including and
  especially other monitors), power lines, or electrical wiring behind walls,
  may produce electromagnetic fields strong enough to cause noticeable
  wiggling, rippling, or other effects. Relocate the monitor or offending
  equipment. Shielding is difficult and expensive.
• Wiring transmitted interference – noisy AC power possibly due to other
  equipment using electric motors (e.g., vacuum cleaners), lamp dimmers or
  motor speed controls (shop tools), fluorescent lamps, and other high power
  devices, may result in a variety of effects. The source is likely local – in
  your house – but could be several miles away. Symptoms might include bars of
  noise moving up or down the screen or diagonally. The effects may be barely
  visible as a couple of jiggling scan lines or be broad bars of salt and
  pepper noise, snow, or distorted video. Plugging the monitor into another
  outlet or the use of a line filter may help. If possible, replace or repair
  the offending device.
• Monitor not locking on one or more video scan ranges – settings of
  video adapter are incorrect. Use software setup program to set these.
  This could also be a fault in the video source or monitor dealing with
  the sync signals.
• Adjustments needed for background brightness or focus – aging CRT reduces
  brightness. Other components may affect focus. These are often easy
  internal (or sometimes external) adjustments but some manufacturers have
  gone to digital setup requiring expensive an adapter (serial cable) to a PC
  and their own (expensive and/or unavailable) software.
• Dead monitor due to power supply problems – very often the causes are
  simple such as bad connections, blown fuse or other component.

Repair or replace

If you need to send or take the monitor to a service center, the repair
could easily exceed half the cost of a new monitor. Service centers
may charge up to $50 or more for providing an initial estimate of repair
costs but this will usually be credited toward the total cost of the repair
(of course, they may just jack this up to compensate for their bench time).
With new monitors going for under $200, the costs of any significant repair
are no longer justifiable unless there is something unique about your monitor.

Some places offer attractive flat rates for repairs involving anything but
the CRT, yoke, and flyback. Such offers are attractive if the repair center
is reputable. However, if by mail, you will be stuck with a tough decision
if they find that one of these expensive components is actually bad.

Monitors become obsolete at a somewhat slower rate than most other electronic
equipment. Therefore, unless you need the higher resolution and scan rates
that newer monitors provide, repairing an older one may make sense as long as
the CRT is in good condition (adequate brightness, no burn marks, good focus).
However, it may just be a good excuse to upgrade.

If you can do the repairs yourself, the equation changes dramatically as
your parts costs will be 1/2 to 1/4 of what a professional will charge
and of course your time is free. The educational aspects may also be
appealing. You will learn a lot in the process. Thus, it may make sense
to repair that old clunker for your 2nd PC (or your 3rd or your 4th or….).

Monitors 101

Subsystems of a monitor

Please refer to Typical SVGA Monitor Block Diagram
while reading the following description.

A computer or video monitor includes the following functional blocks:

1. Low voltage power supply (some may also be part of (2).) Most of the lower
   voltages used in the monitor may be derived from the horizontal deflection
   circuits, a separate switchmode power supply (SMPS), or a combination of
   the two. Rectifier/filter capacitor/regulator from AC line provides the
   B+ to the SMPS or horizontal deflection system. Auto-scan monitors may
   have multiple outputs from the low voltage power supply which are
   selectively switched or enabled depending on the scan rate, or an power
   supply with programmable output voltage for the deflection system.
   A common configuration is a pair of SMPSs where one provides all the fixed
   voltages and the other is programmable based on scan rate.

   Degauss operates off of the line whenever power is turned on (after
   having been off for a few minutes) to demagnetize the CRT. Better
   monitors will have a degauss button which activates this circuitry
   as well since even rotating the monitor on its tilt-swivel base can
   require degauss.

2. Horizontal deflection. These circuits provide the waveforms needed to
   sweep the electron beam in the CRT across and back at anywhere from
   15 kHz to over 100 kHz depending on scan rate and resolution. The
   horizontal sync pulse from the sync separator or the horizontal sync
   input locks the horizontal deflection to the video signal. Auto-scan
   monitors have sophisticated circuitry to permit scanning range of
   horizontal deflection to be automatically varied over a wide range.
3. Vertical deflection. These circuits provide the waveforms needed to
   sweep the electron beam in the CRT from top to bottom and back at
   anywhere from 50 – 120 or more times per second. The vertical sync
   pulse from the sync separator or vertical sync input locks the vertical
   deflection to the video signal. Auto-scan monitors have additional
   circuitry to lock to a wide range of vertical scan rates.
4. CRT high voltage ‘flyback’ power supply (also part of (2).) A modern
   color CRT requires up to 30 kV for a crisp bright picture. Rather than
   having a totally separate power supply, most monitors derive the high
   voltage (as well as many other voltages) from the horizontal deflection
   using a special transformer called a ‘flyback’ or ‘Line OutPut Transformer
   (LOPT) for those of you on the other side of the lake. Some high
   performance monitors use a separate high voltage board or module which is
   a self contained high frequency inverter.
5. Video amplifiers. These buffer the low level inputs from the computer
   or video source. On monitors with TTL inputs (MGA, CGA, EGA), a resistor
   network also combines the intensity and color signals in a kind of poor
   man’s D/A. Analog video amplifiers will usually also include DC restore
   (black level retention, back porch clamping) circuitry stabilize the
   black level on AC coupled video systems.
6. Video drivers (RGB). These are almost always located on a little
   circuit board plugged directly onto the neck of the CRT. They boost
   the output of the video amplifiers to the hundred volts or so needed
   to drive the cathodes (usually) of the CRT.
7. Sync processor. This accepts separate, composite, or ‘sync-on-green’
   signals to control the timing of the horizontal and vertical deflection
   systems. Where input is composite rather than separate H and V syncs (as
   is used with VGA/SVGA), this circuit extracts the individual sync signals.
   For workstation monitors which often have the sync combined with the green
   video signals, it needs to separate this as well. The output of the sync
   processor is horizontal and vertical sync pulses to control the deflection
   circuits.
8. System control. Most higher quality monitors use a microcontroller
   to perform all user interface and control functions from the front panel
   (and sometimes even from a remote control). So called ‘digital monitors’
   meaning digital controls not digital inputs, use buttons for everything
   except possibly user brightness and contrast. Settings for horizontal
   and vertical size and position, pincushion, and color balance for each
   scan rate may be stored in non-volatile memory. It may communicate with
   the video card over the serial VESA bus to inform if of its capabilities.
   The microprocessor also analyzes the input video timing and selects the
   appropriate scan range and components for the detected resolution. While
   these circuits rarely fail, if they do, debugging can be quite a treat.

Most problems occur in the horizontal deflection and power supply sections.
These run at relatively high power levels and some components run hot.
This results in both wear and tear on the components as well as increased
likelihood of bad connections developing from repeated thermal cycles.
The high voltage section is prone to breakdown and arcing as a result
of hairline cracks, humidity, dirt, etc.

The video circuitry is generally quite reliable. However, it seems that
even after 15+ years, manufacturers still cannot reliably turn out circuit
boards that are free of bad solder connections or that do not develop them
with time and use.

For more information on monitor technology

The books listed in the section: Suggested references
include additional information on the theory and implementation of the
technology of monitors and TV sets.

Philips/Magnavox used to have a very nice on-line introduction to a variety
of consumer electronics technologies. Although their site has disappeared –
and even people who work for them have no clue – I have now recovered
several of the articles including those on TVs, VCRs, camcorders, satellite
reception, and connections. See the Introductory Consumer Electronics
Technology Series. These as well as most or all of the other articles,
as well a glossary and much more, can be also
be accessed via the Internet Archive Wayback
Machine. Copy and paste the following URL into the search box:

• http://www.magnavox.com/electreference/electreference.html

The earliest (Nov 09, 1996) archive seems to be the most complete.

On-line tech-tips databases

A number of organizations have compiled databases covering thousands of common
problems with VCRs, TVs, computer monitors, and other electronic equipment.
Most charge for their information but a few, accessible via the Internet, are
either free or have a very minimal monthly or per-case fee. In other cases, a
limited but still useful subset of the for-fee database is freely available.

A tech-tips database is a collection of problems and solutions accumulated by
the organization providing the information or other sources based on actual
repair experiences and case histories. Since the identical failures often
occur at some point in a large percentage of a given model or product line,
checking out a tech-tips database may quickly identify your problem and
solution.

In that case, you can greatly simplify your troubleshooting or at least
confirm a diagnosis before ordering parts. My only reservation with respect
to tech-tips databases in general – this has nothing to do with any one in
particular – is that symptoms can sometimes be deceiving and a solution that
works in one instance may not apply to your specific problem. Therefore,
an understanding of the hows and whys of the equipment along with some good
old fashioned testing is highly desirable to minimize the risk of replacing
parts that turn out not to be bad.

The other disadvantage – at least from one point of view – is that you do not
learn much by just following a procedure developed by others. There is no
explanation of how the original diagnosis was determined or what may have
caused the failure in the first place. Nor is there likely to be any list
of other components that may have been affected by overstress and may fail
in the future. Replacing Q701 and C725 may get your equipment going again
but this will not help you to repair a different model in the future.

Please see the document: On-Line Tech-Tips
Databases for the most up to date compilation of these resources for TVs,
VCRs, computer monitors, and other consumer electronic equipment.

Additional monitor technology and repair information

See Sam’s Neat, Nifty, and Handy Bookmarks
under “Monitor” and “Manuals/Schematics/Repair Guides” for additional links.

CRT Basics

Note: Most of the information on TV and monitor CRT construction, operation,
interference and other problems. has been moved to the document:
TV and Monitor CRT (Picture Tube) Information.
The following is just a brief introduction with instructions on degaussing.

Color CRTs – shadow masks and aperture grills

All color CRTs utilize a shadow mask or aperture grill a fraction of an inch
(1/2″ typical) behind the phosphor screen to direct the electron beams
for the red, green, and blue video signals to the proper phosphor dots.
Since the electron beams for the R, G, and B phosphors originate from
slightly different positions (individual electron guns for each)
and thus arrive at slightly different angles, only the proper phosphors
are excited when the purity is properly adjusted and the necessary
magnetic field free region is maintained inside the CRT. Note that
purity determines that the correct video signal excites the
proper color while convergence determines the geometric
alignment of the 3 colors. Both are affected by magnetic fields.
Bad purity results in mottled or incorrect colors. Bad convergence
results in color fringing at edges of characters or graphics.

The shadow mask consists of a thin steel or InVar (a ferrous alloy)
with a fine array of holes – one for each trio of phosphor
dots – positioned about 1/2 inch behind the surface of the phosphor
screen. With some CRTs, the phosphors are arranged in triangular
formations called triads with each of the color dots at the apex
of the triangle. With many TVs and some monitors, they are
arranged as vertical slots with the phosphors for the 3 colors
next to one another.

An aperture grille, used exclusively in Sony Trinitrons (and now
their clones as well), replaces the shadow mask with an array of finely
tensioned vertical wires. Along with other characteristics of the
aperture grille approach, this permits a somewhat higher possible
brightness to be achieved and is more immune to other problems like
line induced moire and purity changes due to local heating causing
distortion of the shadow mask.

However, there are some disadvantages of the aperture grille design:

• Weight – a heavy support structure must be provided for the tensioned
  wires (like a piano frame).
• Price (proportional to weight).
• Always a cylindrical screen (this may be considered an advantage
  depending on your preference.
• Visible stabilizing wires which may be objectionable or unacceptable
  for certain applications. (Definitely on 15″ and larger sizes, possibly
  on smaller ones as well.)

Apparently, there is no known way around the need to keep the fine
wires from vibrating or changing position due to mechanical shock
in high resolution tubes and thus all Trinitron monitors require
1, 2, or 3 stabilizing wires (depending on tube size) across the
screen which can be see as very fine lines on bright images. Some
people find these wires to be objectionable and for some critical
applications, they may be unacceptable (e.g., medical diagnosis).

Degaussing (demagnetizing) a CRT

Degaussing may be required if there are color purity problems with the
display. On rare occasions, there may be geometric distortion caused
by magnetic fields as well without color problems. The CRT can get
magnetized:

• if the TV or monitor is moved or even just rotated.
• if there has been a lightning strike nearby. A friend of mine
  had a lightning strike near his house which produced all of the
  effects of the EMP from a nuclear bomb.
• If a permanent magnet was brought near the screen (e.g., kid’s
  magnet or megawatt stereo speakers).
• If some piece of electrical or electronic equipment with unshielded
  magnetic fields is in the vicinity of the TV or monitor.

Degaussing should be the first thing attempted whenever color
purity problems are detected. As noted below, first try the
internal degauss circuits of the TV or monitor by power cycling a few
times (on for a minute, off for at least 20 minutes, on for a minute,
etc.) If this does not help or does not completely cure the problem,
then you can try manually degaussing.

Note: Some monitors have a degauss button, and monitors and TVs that are
microprocessor controlled may degauss automatically upon power-on (but may
require pulling the plug to do a hard reset) regardless of the amount of off
time. However, repeated use of these ‘features’ in rapid succession may
result in overheating of the degauss coil or other components. The 20 minutes
off/1 minute on precedure is guaranteed to be safe. (Some others may degauss
upon power-on as long as the previous degauss was not done within some
predetermined amount of time – they keep track with an internal timer.)

Commercial CRT Degaussers are available from parts distributors
like MCM Electronics and consist of a hundred or so turns of magnet wire
in a 6-12 inch coil. They include a line cord and momentary switch. You
flip on the switch, and bring the coil to within several inches of the
screen face. Then you slowly draw the center of the coil toward one edge
of the screen and trace the perimeter of the screen face. Then return to
the original position of the coil being flat against the center of the
screen. Next, slowly decrease the field to zero by backing straight up
across the room as you hold the coil. When you are farther than 5 feet
away you can release the line switch.

The key word here is ** slow **. Go too fast and you will freeze the
instantaneous intensity of the 50/60 Hz AC magnetic field variation
into the ferrous components of the CRT and may make the problem worse.

WARNING: Don’t attempt to degauss inside or in the back of the set (near the
CRT neck. This can demagnetize the relatively weak purity and convergence
magnets which may turn a simple repair into a feature length extravaganza!

It looks really cool to do this while the CRT is powered. The kids will
love the color effects (but then lock your degaussing coil safely away so they
don’t try it on every TV and monitor in the house!).

Bulk tape erasers, tape head degaussers, open frame transformers, and the
“butt-end” of a weller soldering gun can be used as CRT demagnetizers but
it just takes a little longer. (Be careful not to scratch the screen
face with anything sharp. For the Weller, the tip needs to be in place
to get enough magnetic field.) It is imperative to have the CRT running when
using these whimpier approaches, so that you can see where there are
still impurities. Never release the power switch until you’re 4 or 5
feet away from the screen or you’ll have to start over.

I’ve never known of anything being damaged by excess manual degaussing
as long as you don’t attempt to degauss *inside* or the back of the monitor –
it is possible to demagnetize geometry correction, purity, and static
converence magnets in the process! However, I would recommend keeping really
powerful bulk tape erasers-turned-degaussers a couple of inches from the CRT.

Another alternative which has been known to work is to place another similar
size monitor face-to-face with the suspect monitor (take care not to bump or
scratch the screens!) and activate degauss function on the working
monitor. While not ideal, this may be enough to also degauss the broken
one.

If an AC degaussing coil or substitute is unavailable, I have even done
degaussed with a permanent magnet but this is not recommended since it is more
likely to make the problem worse than better. However, if the display
is unusable as is, then using a small magnet can do no harm. (Don’t use
a 20 pound speaker or magnetron magnet as you may rip the shadow mask right
out of the CRT – well at least distort it beyond repair. What I have in
mind is something about as powerful as a refrigerator magnet.)

Keep degaussing fields away from magnetic media. It is a good idea to
avoid degaussing in a room with floppies or back-up tapes. When removing
media from a room remember to check desk drawers and manuals for stray
floppies, too.

It is unlikely that you could actually affect magnetic media but better
safe than sorry. Of the devices mentioned above, only a bulk eraser or
strong permanent magnet are likely to have any effect – and then only when
at extremely close range (direct contact with media container).

All color CRTs include a built-in degaussing coil wrapped around the
perimeter of the CRT face. These are activated each time the CRT is
powered up cold by a 3 terminal thermistor device or other control
circuitry. This is why it is often suggested that color purity problems
may go away “in a few days”. It isn’t a matter of time; it’s the number
of cold power ups that causes it. It takes about 15 minutes of the power
being off for each cool down cycle. These built-in coils with thermal
control are never as effective as external coils.

Note that while the monochrome CRTs used in B/W and projection TVs and mono
monitors don’t have anything inside to get magnetized, the chassis or other
cabinet parts of the equipment may still need degaussing. While this isn’t
likely from normal use or even after being moved or reoriented, a powerful
magnet (like that from a large speaker) could leave iron, steel, or other
ferrous parts with enough residual magnetism to cause a noticeable problem.

See the document: TV and Monitor CRT (Picture Tube)
Information for some additional discussion of degaussing tools,
techniques, treatments for severe magnetization from lightning strikes,
and cautions.

How often to degauss

Some monitor manufacturers specifically warn about excessive use of degauss,
most likely as a result of overstressing components in the degauss circuitry
which are designed (cheaply) for only infrequent use. In particular,
there is often a thermistor that dissipates significant power for the second
or two that the degauss is active. Also, the large coil around the CRT
is not rated for continuous operation and may overheat.

If one or two activations of the degauss button do not clear up the color
problems, manual degaussing using an external coil may be needed
or the monitor may need internal purity/color adjustments. Or, you may have
just installed your megawatt stereo speakers next to the monitor!

You should only need to degauss if you see color purity problems
on your CRT. Otherwise it is unnecessary. The reasons it only works the
first time is that the degauss timing is controlled by a thermistor
which heats up and cuts off the current. If you push the button
twice in a row, that thermistor is still hot and so little happens.

One word of clarification: In order for the degauss operation to be
effective, the AC current in the coil must approach zero before the
circuit cuts out. The circuit to accomplish this often involves a
thermistor to gradually decrease the current (over a matter of several
seconds), and in better monitors, a relay to totally cut off the current
after a certain delay. If the current was turned off suddenly, you would
likely be left with a more magnetized CRT. There are time delay elements
involved which prevent multiple degauss operations in succession. Whether
this is by design or accident, it does prevent the degauss coil – which is
usually grossly undersized for continuous operation – to cool.

Why are there fine lines across my Trinitron monitor or TV?

These are not a defect – they are a ‘feature’.

All Trinitron (or clone) CRTs – tubes that use an aperture grille – require
1, 2, or 3 very fine wires across the screen to stabilize the array of
vertical wires in the aperture grille. Without these, the display would be
very sensitive to any shock or vibration and result in visible shimmering or
rippling. (In fact, even with these stabilizing wires, you can usually see
this shimmering if you whack a Trinitron monitor.) The lines you see are the
shadows cast by these fine wires.

The number of wires depends on the size of the screen. Below 15″ there
is usually a single wire; between 15″ and 21″ there are usually 2 wires;
above 21″ there may be 3 wires. (Some very small Trinitron CRTs may not
need these but they will be present on most of the sizes of interest here.)

Only you can decide if this deficiency is serious enough to avoid the
use of a Trinitron based monitor. Some people never get used to the fine
lines but many really like the generally high quality of Trinitron based
displays and eventually totally ignore them.

Monitor Placement and Preventive Maintenance

General monitor placement considerations

Proper care of a monitor does not require much. Following the recommendations
below will assure long life and minimize repairs:

• Subdued lighting is preferred for best viewing conditions. Avoid direct
  overhead light falling on the screen or coming from behind the monitor
  if possible.
• Locate the monitor away from extremes of hot and cold. Avoid damp or dusty
  locations if possible. (Right you say, keep dreaming!) This will help
  keep your PC happy as well.
• Allow adequate ventilation – monitors use a fair amount of power – from
  60 watts for a 12 inch monochrome monitor to over 200 W for a 21 inch
  high resolution color monitor. Heat is one major enemy of electronics.
• Do not put anything on top of the monitor that might block the ventilation
  grill in the rear or top of the cover. This is the major avenue for
  the convection needed to cool internal components.
• Do not place two monitors close to one another. The magnetic fields
  may cause either or both to suffer from wiggling or shimmering images.
  Likewise, do not place a monitor next to a TV if possible.
• Locate loudspeakers and other sources of magnetic fields at least a couple
  of feet from the monitor. This will minimize the possibility of color purity
  or geometry problems. The exception is with respect to good quality shielded
  multimedia speakers which are designed to avoid magnetic interference
  problems.

  Other devices which may cause interference include anything with power
  transformers including audio equipment, AC or DC wall adapters, and laptop
  power supplies; fluorescent lamps with magnetic ballasts; and motorized
  or heavy duty appliances.

• Situate monitors away from power lines – even electric wiring behind
  or on the other side of walls – and heavy equipment which may cause
  noticeable interference like rippling, wiggling, or swimming of the
  picture. Shielding is difficult and expensive.
• Make sure all video connections are secure (tighten the thumbscrews)
  to minimize the possibility of intermittent or noisy colors. Keep the
  cables as short as possible. Do not add extension cables if at all
  possible as these almost always result in a reduction in image crispness
  and introduce ghosting, smearing, and other termination problems.
  If you must add an extension, use proper high quality cable only long
  enough to make connections conveniently. Follow the termination
  recommendations elsewhere in this document.
• Finally, store magnetic media well away from all electronic equipment
  including and especially monitors and loudspeakers. Heat and magnetic
  fields will rapidly turn your diskettes and tapes into so much trash. The
  operation of the monitor depends on magnetic fields for beam deflection.
  Enough said.

Non-standard monitor mounting considerations

Monitors normally are positioned horizontally or via the limits of their tilt
swivel bases out in the open on a table or desktop. However, for use in
exhibits or for custom installations, it may be desirable to mount a monitor
in a non-standard position and/or inside an enclosure.

(From: Bob Myers (myers@fc.hp.com).)

Your mileage may vary, but (and please take the following for what it is, a
very general answer)…

There are basically two potential problems here; one is cooling, and the other
is the fact that the monitor has no doubt been set up by the factory assuming
standard magnetic conditions, which probably DIDN’T involve the monitor
tilting at much of an angle. If you’re happy with the image quality when it’s
installed in the cabinet, that leaves just the first concern. THAT one can be
addressed by simply making sure the cabinet provides adequate ventilation (and
preferably adding a fan for a bit of forced-air cooling), and making sure that
the whole installation isn’t going to be exposed to high ambient temperatures.
(Most monitors are speced to a 40 deg. C ambient in their normal orientation;
adding forced-air cooling will usually let you keep that rating in positions
somewhat beyond the normal.) Under no circumstances should you block the
cabinet’s vents, and – depending on the installation – it may be preferable to
remove the rear case parts of the monitor (but NOT the metal covers beneath
the plastic skin) in order to improve air circulation.

Your best bet is to simply contact the service/support people of the monitor
manufacturer, and get their input on the installation. Failing to get the
manufacturer’s blessing on something like this most often voids the warranty,
and can probably lead to some liability problems. (Note – I’m not a lawyer,
and I’m not about to start playing one on the net.)

Preventive maintenance – care and cleaning

Preventive maintenance for a monitor is pretty simple – just keep the case
clean and free of obstructions. For CRT monitors, clean the screen with a
soft cloth just dampened with water and mild detergent or isopropyl alcohol.
This will avoid damage to normal as well as antireflection coated glass. DO
NOT use anything so wet that liquid may seep inside of the monitor around
the edge of the CRT. You could end up with a very expensive repair bill when
the liquid decides to short out the main circuit board lurking just below.
Then dry thoroughly. Use the CRT sprays sold in computer stores if you
like but again, make sure none can seep inside. If you have not cleaned
the screen for quite a while, you will be amazed at the amount of black
grime that collects due to the static buildup from the CRT high voltage
supply.

There is some dispute as to what cleaners are safe for CRTs with antireflective
coatings (not the etched or frosted variety). Water, mild detergent, and
isopropyl alcohol should be safe. Definitely avoid the use of anything with
abrasives for any type of monitor screen. And some warn against products with
ammonia (which may include Windex, Top-Job, and other popular cleaners), as
this may damage/remove some types of antireflective coatings. To be doubly
sure, test a small spot in a corner of the screen.

In really dusty situations, periodically vacuuming inside the case and the use
of contact cleaner for the controls might be a good idea but realistically,
you will not do this so don’t worry about it.

Note that a drop of oil or other contamination might appear like a defect
(hole) in the AR coating. Before getting upset, try cleaning the screen.

For LCD TVs, LCD computer monitors, and laptop displays, the cleaning is
particularly critical. The front surface of these facing the viewer is
generally not made of glass like those in CRT displays, but rather a plastic
layer or film. Thus, any cleaning method that uses harsh chemicals
can permanently damage the screen, with or without an
anti-reflection coating. Some glass cleaners, acetone (nail polish
remover), and other strong solvents can attack the plastic very quickly.
By the time you realize there is damage, it may be too late.
And, of course, NEVER use anything even mildly abrasive.

A damp cloth with soap or detergent and water is
safe, as is generally a damp clost with a solution of 70 percent isopropyl
(rubbing) alcohol diluted in the ratio 1:1 with water.

And it is even more essential to avoid allowing any liguid to seep inside
along the edges as this can short out the circuitry, especially the high
voltage back-light driver,which often located behind the trim at the bottom,
and possibly ruin the display entirely, or at least requiring a major repair.

(From: Bob Myers (myers@fc.hp.com).)

Windex is perfectly fine for the OCLI HEA coating or equivalents; OCLI’s
coating is pretty tough and chemical-resistant stuff. There may be
alternative (er..cheaper) coatings in use which could be damaged by various
commercial cleaners, (For what it’s worth, OCLI also sells their own brand of
glass cleaner under the name “TFC”, for “Thin Film Cleaner”.)

I have cleaned monitors of various brands with both Windex and the OCLI-brand
cleaner, with no ill results. But then, I’m usually pretty sure what sort of
coating I’m dealing with… 🙂

Monitor coatings are always changing; besides the basic “OCLI type”
quarter-wave coatings and their conductive versions developed to address
E-field issues, just about every tube manufacturer has their own brew or three
of antiglare/antistatic coatings. There are also still SOME tubes that aren’t
really coated at all, but instead are using mechanically or chemically etched
faceplates as a cheap “anti-glare” (actually, glare-diffusing) treatment.

In general, look in the user guide/owner’s manual and see what your monitor’s
manufacturer recommends in the way of cleaning supplies.

(From: Tom Watson (tsw@johana.com).)

If you are maintaining a site, consider periodic cleaning of the monitors.
Depending on the location, they can accumulate quite a bit of dust. In normal
operation there is a electrostatic charge on the face of the crt (larger
screens have bigger charges) which act as ‘dust magnets’. If the operator
smokes (thankfully decreasing), it is even worse. At one site I helped out
with, most of the operators smoked, and the screens slowly got covered with a
film of both dust and smoke particles. A little bit of glass cleaner applied
with reasonable caution and the decree of “adjustments” to make the screen
better (these were character monochrome terminals), and lo and behold, “what
an improvement!”. Yes, even in my dusty house, the TVs get a coating of
film/goo which needs to be cleaned, and the picture quality (BayWatch viewers
beware) improves quite a bit. Try this on your home TV to see what comes off,
then show everyone else. You will be surprised what a little bit of cleaning
does.

(From: Bob Myers (myers@fc.hp.com).)

1. Don’t block the vents; make sure the monitor has adequate ventilation,
   and don’t operate it more than necessary at high ambient temperatures.
2. If the monitor is used in particularly dusty environments, it’s probably
   a good idea to have a qualified service tech open it up every so often
   (perhaps once a year, or more often depending on just how dirty it gets)
   and clean out the dust.
3. The usual sorts of common-sense things – don’t subject the monitor to
   mechanical shock and vibration, clean up spills, etc., promptly, and
   so forth. And if you’re having repeated power-supply problems with your
   equipment, it may be time to get suspicious of the quality of your AC
   power (are you getting noise on the line, sags, surges, spikes, brownouts,
   that sort of thing?).

And most importantly:

1. Turn the monitor OFF when it’s not going to be used for an extended
   period (such as overnight, or if you’ll be away from your desk for the
   afternoon, etc.). Heat is the enemy of all electronic components, and
   screen-savers do NOTHING in this regard. Many screen-savers don’t even
   do a particularly good job of going easy on the CRT. With modern
   power-management software, there’s really no reason to be leaving a
   monitor up and running all the time.

These won’t guarantee long life, of course – nothing can do that, as there
will always be the possibility of the random component failure. But these
are the best that the user can do to make sure the monitor goes as long as
it can.

Monitor tuneup?

(From: Bob Myers (myers@fc.hp.com).)

Most manufacturers will quote an MTBF (Mean Time Before Failure) of
somewhere in the 30,000 to 60,000 hour range, EXCLUSIVE OF the CRT. The
typical CRT, without an extended-life cathode, is usually good for
10,000 to 15,000 hours before it reaches half of its initial brightness.
Note that, if you leave your monitor on all the time, a year is just about
8,000 hours.

The only “tuneup” that a monitor should need, exclusive of adjustments
needed following replacement of a failed component, would be video amplifier
and/or CRT biasing adjustments to compensate for the aging of the tube.
These are usually done only if you’re using the thing in an application where
exact color/brightness matching is important. Regular degaussing of the
unit may be needed, of course, but I’m not considering that a “tuneup” or
adjustment.

Monitor Troubleshooting

SAFETY

TVs and computer or video monitors are among the more dangerous of consumer
electronic equipment when it comes to servicing. (Microwave ovens are
probably the most hazardous due to high voltage at flesh frying and cardiac
arresting high power.)

There are two areas which have particularly nasty electrical dangers: the
non-isolated line power supply and the CRT high voltage.

Major parts of nearly all modern TVs and many computer monitors are directly
connected to the AC line – there is no power transformer to provide the
essential barrier for safety and to minimize the risk of equipment damage.
In the majority of designs, the live parts of the TV or monitor are limited
to the AC input and line filter, degauss circuit, bridge rectifier and main
filter capacitor(s), low voltage (B+) regulator (if any), horizontal output
transistor and primary side of the flyback (LOPT) transformer, and parts
of the startup circuit and standby power supply. The flyback generates most
of the other voltages used in the unit and provides an isolation barrier so
that the signal circuits are not line connected and safer.

Since a bridge rectifier is generally used in the power supply, both
directions of the polarized plug result in dangerous conditions and an
isolation transformer really should be used – to protect you, your test
equipment, and the TV, from serious damage. Some TVs do not have any
isolation barrier whatsoever – the entire chassis is live. These are
particularly nasty.

The high voltage to the CRT, while 200 times greater than the line input,
is not nearly as dangerous for several reasons. First, it is present in a
very limited area of the TV or monitor – from the output of the flyback
to the CRT anode via the fat HV wire and suction cup connector. If you
don’t need to remove the mainboard or replace the flyback or CRT, then
leave it alone and it should not bite. Furthermore, while the shock from
the HV can be quite painful due to the capacitance of the CRT envelope, it
is not nearly as likely to be lethal since the current available from the
line connected power supply is much greater.

Of particular note in: Major Parts of Typical SVGA
Monitor with Cover Removed are the CRT HV cable and connector, flyback
or LOPT, and the horizontal output transistor and its heat sink. With many
TVs and some monitors, this may be line-connected and electrically hot.
However, this monitor uses a separate switchmode power supply and in any case,
there is likely an insulator between the transistor and heat sink.

Safety Guidelines:

These guidelines are to protect you from potentially deadly electrical shock
hazards as well as the equipment from accidental damage.

Note that the danger to you is not only in your body providing a conducting
path, particularly through your heart. Any involuntary muscle contractions
caused by a shock, while perhaps harmless in themselves, may cause collateral
damage – there are many sharp edges inside this type of equipment as well as
other electrically live parts you may contact accidentally.

The purpose of this set of guidelines is not to frighten you but rather to
make you aware of the appropriate precautions. Repair of TVs, monitors,
microwave ovens, and other consumer and industrial equipment can be both
rewarding and economical. Just be sure that it is also safe!

• Don’t work alone – in the event of an emergency another person’s presence
  may be essential.
• Always keep one hand in your pocket when anywhere around a powered
  line-connected or high voltage system.
• Wear rubber bottom shoes or sneakers.
• Don’t wear any jewelry or other articles that could accidentally contact
  circuitry and conduct current, or get caught in moving parts.
• Set up your work area away from possible grounds that you may accidentally
  contact.
• Know your equipment: TVs and monitors may use parts of the metal chassis
  as ground return yet the chassis may be electrically live with respect to the
  earth ground of the AC line. Microwave ovens use the chassis as ground
  return for the high voltage. In addition, do not assume that the chassis
  is a suitable ground for your test equipment!
• If circuit boards need to be removed from their mountings, put insulating
  material between the boards and anything they may short to. Hold them in
  place with string or electrical tape. Prop them up with insulation sticks –
  plastic or wood.
• If you need to probe, solder, or otherwise touch circuits with power off,
  discharge (across) large power supply filter capacitors with a 2 W or greater
  resistor of 100 to 500 ohms/V approximate value (e.g., for a 200 V capacitor,
  use a 20K to 100K ohm resistor). Monitor while discharging and verify that
  there is no residual charge with a suitable voltmeter. In a TV or monitor,
  if you are removing the high voltage connection to the CRT (to replace the
  flyback transformer for example) first discharge the CRT contact (under the
  suction cup at the end of the fat HV wire). Use a 1M to 10M ohm 5 W or
  greater wattage (for its voltage holdoff capability, not power dissipation)
  resistor on the end of an insulating stick or the probe of a high voltage
  meter. Discharge to the metal frame which is connected to the outside of
  the CRT.
• For TVs and monitors in particular, there is the additional danger of
  CRT implosion – take care not to bang the CRT envelope with your tools.
  An implosion will scatter shards of glass at high velocity in every
  direction. There are several tons of force attempting to crush the typical
  CRT. While implosion is not really likely even with modest abuse, why take
  chances? However, the CRT neck is relatively thin and fragile and breaking
  it would be very embarrassing and costly. Always wear eye protection when
  working around the back side of a CRT.
• Connect/disconnect any test leads with the equipment unpowered and
  unplugged. Use clip leads or solder temporary wires to reach cramped
  locations or difficult to access locations.
• If you must probe live, put electrical tape over all but the last 1/16″
  of the test probes to avoid the possibility of an accidental short which
  could cause damage to various components. Clip the reference end of the
  meter or scope to the appropriate ground return so that you need to only
  probe with one hand.
• Perform as many tests as possible with power off and the equipment unplugged.
  For example, the semiconductors in the power supply section of a TV or
  monitor can be tested for short circuits with an ohmmeter.
• Use an isolation transformer if there is any chance of contacting line
  connected circuits. A Variac(tm) is not an isolation transformer!
  The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a
  good idea but will not protect you from shock from many points in a line
  connected TV or monitor, or the high voltage side of a microwave oven, for
  example. (Note however, that, a GFCI may nuisanse trip at power-on or at
  other random times due to leakage paths (like your scope probe ground) or
  the highly capacitive or inductive input characteristics of line powered
  equipment.) A fuse or circuit breaker is too slow and insensitive to provide
  any protection for you or in many cases, your equipment. However, these
  devices may save your scope probe ground wire should you accidentally connect
  it to a live chassis.
• Don’t attempt repair work when you are tired. Not only will you be more
  careless, but your primary diagnostic tool – deductive reasoning – will
  not be operating at full capacity.
• Finally, never assume anything without checking it out for yourself!
  Don’t take shortcuts!

Warning about disconnecting CRT neck board

Some manufacturers warn against powering a TV or monitor CRT without the
CRT neck board connected. Apparently, without something – anything –
to drain the charge resulting from the current flow due to residual gas ions
inside the CRT, the shortest path may be through the glass neck of the tube
to the yoke or from the pins outside the CRT to whatever is nearby. There
aren’t many ions in a modern CRT but I suppose a few here, a few there, and
eventually they add up to enough to cause a major disaster at least on some
CRTs.

This is probably not a problem on small CRTs but for large ones with high
high voltages and high deflection angles where the glass of the neck is
very thin to allow for maximum deflection sensitivity, the potential does
exist for arcing through the glass to the yoke to occur, destroying the CRT.

There is really no way to know which models will self destruct but it
should be possible to avoid such a disaster by providing a temporary return
path to the DAG ground of the CRT (NOT SIGNAL GROUND!!) via the focus or G2
pins preferably through a high value high voltage rated resistor just in
case one of these is shorted.

This probably applies mostly to large direct-view TVs since they use high
deflection angle CRTs but it won’t hurt to take appropriate precautions with
video and computer monitors as well.

Troubleshooting tips

Many problems have simple solutions. Don’t immediately assume that
your problem is some combination of esoteric complex convoluted
failures. For a monitor, it may just be a bad connection or blown fuse.
Remember that the problems with the most catastrophic impact on operation
like a dead monitor usually have the simplest solutions. The kind of
problems we would like to avoid at all costs are the ones that are
intermittent or difficult to reproduce: the occasional jitter or a monitor
that blows its horizontal output transistor every six months.

If you get stuck, sleep on it. Sometimes, just letting the problem
bounce around in your head will lead to a different more successful
approach or solution. Don’t work when you are really tired – it is both
dangerous (especially with respect to monitors) and mostly non-productive
(or possibly destructive).

Whenever working on complex equipment, make copious notes and diagrams.
You will be eternally grateful when the time comes to reassemble the unit.
Most connectors are keyed against incorrect insertion or interchange
of cables, but not always. Apparently identical screws may be of differing
lengths or have slightly different thread types. Little parts may fit in
more than one place or orientation. Etc. Etc.

Pill bottles, film canisters, and plastic ice cube trays come in handy for
sorting and storing screws and other small parts after disassembly. This
is particularly true if you have repairs on multiple pieces of equipment
under way simultaneously.

Select a work area which is wide open, well lighted, and where dropped
parts can be located – not on a deep pile shag rug. The best location will
also be relatively dust free and allow you to suspend your troubleshooting
to eat or sleep or think without having to pile everything into a cardboard
box for storage.

Another consideration is ESD – Electro-Static Discharge. Some components
(like ICs) in a TV are vulnerable to ESD. There is no need to go overboard
but taking reasonable precautions such as getting into the habit of touching
a **safe** ground point first.

WARNING: even with an isolation transformer, a live chassis should **not** be
considered a safe ground point. When the monitor is unplugged, the shields
or other signal ground points should be safe and effective.

A basic set of precision hand tools will be all you need to disassemble
a monitor and perform most adjustments. These do not need to be really
expensive but poor quality tools are worse than useless and can cause
damage. Needed tools include a selection of Philips and straight blade
screwdrivers, socket drivers, needlenose pliers, wire cutters, tweezers,
and dental picks. For adjustments, a miniature (1/16″ blade) screwdriver
with a non-metallic tip is desirable both to prevent the presence of
metal from altering the electrical properties of the circuit and to
minimize the possibility of shorting something from accidental contact
with the circuitry. A set of plastic alignment tools will be useful for
making adjustments to coils (though you can forgo these until the (rare)
need arises.

A low power (e.g., 25 W) fine tip soldering iron and fine rosin core solder
will be needed if you should need to disconnect any soldered wires (on purpose
or by accident) or replace soldered components. A higher power iron or small
soldering gun will be needed for dealing with larger components. Never use
acid core solder or the type used for sweating copper pipes!

CAUTION: You can easily turn a simple repair (e.g., bad solder connections)
into an expensive mess if you use inappropriate soldering equipment and/or
lack the soldering skills to go along with it. If in doubt, find someone else
to do the soldering or at least practice, practice, practice, soldering and
desoldering on a junk circuit board first! See the document:
Troubleshooting and Repair of Consumer Electronic
Equipment for additional info on soldering and rework techniques.

For thermal or warmup problems, a can of ‘cold spray’ or ‘circuit chiller’
(they are the same) and a heat gun or blow dryer come in handy to identify
components whose characteristics may be drifting with temperature. Using the
extension tube of the spray can or making a cardboard nozzle for the heat
gun can provide very precise control of which components you are affecting.

For info on useful chemicals, adhesives, and lubricants, see “Repair Briefs,
an Introduction” as well as other documents available at this site.

Test equipment

Don’t start with the electronic test equipment, start with some analytical
thinking. Your powers of observation (and a little experience) will make
a good start. Your built in senses and that stuff between
your ears represents the most important test equipment you have.

However, some test equipment will be needed:

• Multimeter (DMM or VOM) – This is essential for checking of power supply
  voltages and voltages on the pins of ICs or other components – service
  literature like the SAMs Photofacts described elsewhere in this document
  include voltage measurements at nearly every circuit tie point for properly
  functioning equipment. The multimeter will also be used to check
  components like transistors, resistors, and capacitors for correct value
  and for shorts or opens. You do not need a fancy instrument. A basic
  DMM – as long as it is reliable – will suffice for most troubleshooting.
  If you want one that will last for many years, go with a Fluke. However,
  even the mid range DMMs from Radio Shack have proven to be reliable and
  of acceptable accuracy. For some kinds of measurements – to deduce trends
  for example – an analog VOM is preferred (though some DMMs have a bar graph
  scale which almost as good).
• Oscilloscope – While many problems can be dealt with using just a
  multimeter, a ‘scope will be essential as you get more into advanced
  troubleshooting. Basic requirements are: dual trace, 10-20 MHz minimum
  vertical bandwidth, delayed sweep desirable but not essential. A good set
  of proper 10X/1X probes. Higher vertical bandwidth is desirable but most
  consumer electronics work can be done with a 10 MHz scope. A storage scope
  or digital scope might be desirable for certain tasks but is by no means
  essential for basic troubleshooting.

  I would recommend a good used Tektronix (Tek) or Hewlett Packard (HP)
  scope over a new scope of almost any other brand. You will usually get
  more scope for your money and these things last almost forever. Until
  recently, my ‘good’ scope was the militarized version (AN/USM-281A) of
  the HP180 lab scope. It has a dual channel 50 MHz vertical plugin and
  a delayed sweep horizontal plugin. I have seen these going for under
  $300 from surplus outfits. For a little more money, you can get a
  Tek 465 or 465B (newer version but similar specifications) 100 Mhz
  scope ($200 to $600, sometimes cheaper on eBay or elsewhere but there
  is more risk than buying from a reputable dealer). I have now acquired
  a Tek 465B and that’s what I use mostly these days. The HP-180 is still
  fine but I couldn’t pass up a really good deal. 🙂 The Tek 465/B or other
  similar model will suffice for all but the most demanding (read: RF or
  high speed digital) repairs.

• A video signal source – depending on what type of monitor you are
  repairing, you may need both computer and television signals.

  Computer Monitors – a test PC is useful as a video source. Of course,
  it will need to support whatever scan rates and video types the
  monitor is designed to accept. Software programs are available to
  display purity, convergence, focus, color, and other test patterns.
  Or create your own test patterns using a program like Windows Paint.
  See the section: Using a PC as a monitor test
  pattern generator.

  Studio monitors – a baseband video source like a VCR or camcorder
  is useful in lieu of a test pattern generator. These will allow you to
  you to control the program material. In fact, making some test tapes
  using a camcorder or video camera to record static test patterns will
  allow you full control of what is being displayed and for how long.

• Color bar/dot/crosshatch signal generator. This is a useful piece
  of equipment if you are doing a lot of TV or studio monitor repair and
  need to perform CRT convergence and chroma adjustments. However, there
  are alternatives that are almost as good: a VHS recording of these
  test patterns will work for TVs. A PC programmed to output a suitable
  set of test patterns will be fine for monitors (and TVs if you can set
  up the video card to produce an NTSC/PAL signal. This can be put
  through a VCR to generate the RF (Channel 3/4) input to your TV if
  it does not have direct video inputs (RCA jacks).

  Sophisticated (and expensive) universal test pattern generators are available
  that will handle any possible monitor scan rate.

Incredibly handy widgets

These are the little gadgets and homemade testers that are useful for many
repair situations. Here are just a few of the most basic:

• Series light bulb for current limiting during the testing of TVs,
  monitors, switching power supplies, audio power amplifiers, etc. I built
  a dual outlet box with the outlets wired in series so that a lamp
  can be plugged into one outlet and the device under test into the other.
  For added versatility, add a regular outlet and ‘kill’ switch using a
  quad box instead. The use of a series load will prevent your expensive
  replacement part like a horizontal output transistor from blowing if
  there is still some fault in the circuit you have failed to locate.
• A Variac. It doesn’t need to be large – a 2 A Variac mounted with
  a switch, outlet and fuse will suffice for most tasks. However,
  a 5 amp or larger Variac is desirable. If you will be troubleshooting
  220 VAC equipment in the US, there are Variacs that will output 0-240 VAC
  from a 115 VAC line (just make sure you don’t forget that this can easily
  fry your 115 VAC equipment.) By varying the line voltage, not only can
  you bring up a newly repaired monitor gradually to make sure there are no
  problems; you can also evaluate behavior at low and high line voltage.
  This can greatly aid in troubleshooting power supply problems. Warning:
  a Variac is not an isolation transformer and does not help with respect
  to safety. You need an isolation transformer as well.
• Isolation transformer. This is very important for safely working on
  live chassis equipment. Since nearly all modern monitors utilize line
  connected switchmode power supply or line connected deflection circuits,
  it is essential. You can build one from a pair of similar
  power transformers back-to-back (with their highest rated secondaries
  connected together. I built mine from a couple of similar old
  tube type TV power transformers mounted on a board with an outlet box
  including a fuse. Their high voltage windings were connected together.
  The unused low voltage windings can be put in series with the primary
  or output windings to adjust voltage. Alternatively, commercial line
  isolation transformers suitable for TV troubleshooting are available
  for less than $100 – well worth every penny.
• Variable isolation transformer. You don’t need to buy a fancy combination
  unit. A Variac can be followed by a normal isolation transformer. (The
  opposite order also works. There may be some subtle differences in
  load capacity.).

CAUTION: Keep any large transformer of this type well away from your monitor
or TV. The magnetic field it produces may cause the picture to wiggle or the
colors to become messed up – and you to think there is an additional problem!

• Degaussing coil. Make or buy. The internal degaussing coil salvaged
  from a defunct color TV or monitor doubled over to half it original diameter
  to increase its strength in series with a 200 W light bulb for current
  limiting will work just fine. Or, buy one from a place like MCM Electronics
  for about $15-$30 that will be suitable for all but the largest TVs and
  monitors. Also, see the section: Degaussing
  (demagnetizing) a CRT.

Safe discharging of capacitors in TVs and video monitors

It is essential – for your safety and to prevent damage to the device under
test as well as your test equipment – that large or high voltage capacitors
be fully discharged before measurements are made, soldering is attempted,
or the circuitry is touched in any way. Some of the large filter capacitors
commonly found in line operated equipment store a potentially lethal charge.

This doesn’t mean that every one of the 250 capacitors in your TV need to be
discharged every time you power off and want to make a measurement. However,
the large main filter capacitors and other capacitors in the power supplies
should be checked and discharged if any significant voltage is found after
powering off (or before any testing – the CRT capacitance in a TV or video
monitor, for example, can retain a dangerous or at least painful charge for
days or longer!)

The technique I recommend is to use a high wattage resistor of about
100 ohms/V of the working voltage of the capacitor. This will
prevent the arc-welding associated with screwdriver discharge but will
have a short enough time constant so that the capacitor will drop to
a low voltage in at most a few seconds (dependent of course on the
RC time constant and its original voltage).

Then check with a voltmeter to be double sure. Better yet, monitor
while discharging (not needed for the CRT – discharge is nearly
instantaneous even with multi-M ohm resistor).

Obviously, make sure that you are well insulated!

• For the main capacitors in a TV or monitor power supply which might be
  400 uF at 200 V, this would mean a 5K, 10W resistor. RC = 2 seconds.
  5RC = 10 seconds. A lower wattage resistor can be used since the total
  energy in not that great. If you want to be more high tech, you can
  build the capacitor discharge circuit outlined in the companion
  document: Capacitor Testing, Safe Discharging, and
  Other Related Information. This provides a visible indication of
  remaining charge and polarity.
• For the CRT, use a several M ohm resistor good for 30 kV or more (or a
  string of lower value resistors to obtain this voltage rating). A 1/4 watt
  job will just arc over! Discharge to the chassis ground connected to the
  outside of the CRT – NOT SIGNAL GROUND ON THE MAIN BOARD as you may damage
  sensitive circuitry. The time constant is very short – a ms or so.
  However, repeat a few times to be sure, then use a shorting clip as these
  capacitors have a way of recovering a painful charge if left alone – there
  have been too many stories of painful experiences from charge developing for
  whatever reasons ready to bite when the HV lead is reconnected.

  Note that if you are touching the little board on the neck of the CRT, you
  may want to discharge the HV even if you are not disconnecting the fat red
  wire – the focus and screen (G2) voltages on that board are derived from the
  CRT HV.

  WARNING: Most common resistors – even 5 W jobs – are rated for only a few
  hundred volts and are not suitable for the 25 kV or more found in modern
  TVs and monitors. Alternatives to a long string of regular resistors are
  a high voltage probe or a known good focus/screen divider network. However,
  note that the discharge time constant with these may be a few seconds. Also
  see the section: Additional information on discharging
  CRTs.

  If you are not going to be removing the CRT anode connection, replacing
  the flyback, or going near the components on the little board on the neck
  of the CRT, I would just stay away from the fat red wire and what it is
  connected to including the focus and screen wires. Repeatedly shoving
  a screwdriver under the anode cap risks scratching the CRT envelope which
  is something you really do not want to do.

Again, always double check with a reliable voltmeter!

Reasons to use a resistor and not a screwdriver to discharge capacitors:

1. It will not destroy screwdrivers and capacitor terminals.
2. It will not damage the capacitor (due to the current pulse).
3. It will reduce your spouse’s stress level in not having to hear those
   scary snaps and crackles.

Additional information on discharging CRTs

You may hear that it is only safe to discharge from the Ultor to the Dag.
So, what the @#$% are they talking about? :-).

(From: Asimov (mike.ross@juxta.mnet.pubnix.ten).)

‘Dag’ is short for Aquadag. It is a type of paint made of a graphite pigment
which is conductive. It is painted onto the inside and outside of picture
tubes to form the 2 plates of a high voltage filter capacitor using the glass
in between as dielectric. This capacitor is between .005uF and .01uF in
value. This seems like very little capacity but it can store a substantial
charge with 25,000 volts applied.

The outside “Dag” is always connected to the circuit chassis ground via a
series of springs, clips, and wires around the picture tube. The high voltage
or “Ultor” terminal must be discharged to chassis ground before working on the
circuit especially with older TV’s which didn’t use a voltage divider to
derive the focus potential or newer TV’s with a defective open divider.

(From: Sam)

CAUTION: The Dag coating/springs/clips/etc. may not be the same as signal
ground on the mainboard. Discharging to that instead could result in all
sorts of expensive blown components. Discharging between the CRT anode cap
and Dag should be low risk though it is best to use a HV probe or properly
rated high value resistor.

For more details, see the document: TV and Monitor CRT
(Picture Tube) Information.

Removing the CRT HV connector

WARNING: Make sure the CRT has been discharged FIRST!

The rubber part is usually not glued down so it can be lifted rather easily.
However, there may be some silicone type grease between the rubber boot (that
looks like a suction cup) and the CRT glass to seal out dust.

A metal clip with a spring keeping it spread out attaches inside the button.

While there are a variety of types of clips actually used, pushing the
connector to one side and/or squeezing it in the appropriate direction (peel
up one side of the rubber to inspect) while gently lifting up should free it.
Probably :-).

The clip (when removed) and CRT button look sort of like this:

                       ||======= HV Cable
                       /\
               Clip   |  |
          (Removed)  _|  |_
                               (No DAG coating in vicinity of HV connector)
        ____________.-    -.___________
   CRT  ____________|______|___________ Glass
                  Metal Button

Replacement is done in reverse order!

This isn’t rocket science and excessive force should not be needed! 🙂

The series light bulb trick

When powering up a monitor (or any other modern electronic devices with
expensive power semiconductors) that has had work done on any power circuits,
it is desirable to minimize the chance of blowing your newly installed parts
should there still be a fault. There are two ways of doing this: use of a
Variac to bring up the AC line voltage gradually and the use of a series load
to limit current to power semiconductors.

Actually using a series load – a light bulb is just a readily available
cheap load – is better than a Variac (well both might be better still) since
it will limit current to (hopefully) non-destructive levels.

What you want to do is limit current to the critical parts – usually the
horizontal output transistor (HOT). Most of the time you will get away with
putting it in series with the AC line. However, sometimes, putting a light
bulb directly in the B+ circuit will be needed to provide adequate protection.
In that location, it will limit the current to the HOT from the main filter
capacitors of line connected power supplies. This may also be required with
some switchmode power supplies as they can still supply bursts of full (or
excessive) current even if there is a light bulb in series with the AC line.

Actually, an actual power resistor is probably better as its resistance is
constant as opposed to a light bulb which will vary by 1:10 from cold to hot.
The light bulb, however, provides a nice visual indication of the current
drawn by the circuit under test. For example:

• Full brightness: short circuit or extremely heavy load – a fault probably
  is still present.
• Initially bright but then settles at reduced brightness: filter capacitors
  charge, then lower current to rest of circuit. This is what is expected
  when the equipment is operating normally. There could still be a problem
  with the power circuits but it will probably not result in an immediate
  catastrophic failure.
• Pulsating: power supply is trying to come up but shutting down due to
  overcurrent or overvoltage condition. This could be due to a continuing
  fault or the light bulb may be too small for the equipment.

Note: for a TV or monitor, it may be necessary (and desirable) to unplug the
degauss coil as this represents a heavy initial load which may prevent the unit
from starting up with the light bulb in the circuit.

The following are suggested starting wattages:

• 40 W bulb for VCR or laptop computer switching power supplies.
• 100 W bulb for small (i.e., B/W or 13 inch color) monitors or TVs.
• 150-200 W bulb for large color monitors or projection TVs.

A 50/100/150 W (or similar) 3-way bulb in an appropriate socket comes in
handy for this but mark the switch so that you know which setting is which!

Depending on the power rating of the equipment, these wattages may need to be
increased. I have had to go to a 300 W light bulb for some computer monitors.
However, start low. If the bulb lights at full brightness, you know there is
still a major fault. If it flickers or the TV (or other device) does not quite
come fully up, then it should be safe to go to a larger bulb. Resist the
temptation to immediately remove the bulb at this point – I have been screwed
by doing this. Try a larger one first. The behavior should improve. If it
does not, there is still a fault present.

Note that some TVs and monitors simply will not power up at all with any kind
of series load – at least not with one small enough (in terms of wattage) to
provide any real protection. The microcontroller apparently senses the drop
in voltage and shuts the unit down or continuously cycles power. Fortunately,
these seem to be the exceptions.

Getting inside a monitor

You will void the warranty – at least in principle. There are usually no
warranty seals on a monitor so unless you cause visible damage or mangle the
screws or plastic, it is unlikely that this would be detected. You need to
decide. A monitor still under warranty should probably be returned for
warranty service for any covered problems except those with the most obvious
and easy solutions. Another advantage of using warranty service is that
should your problem actually be covered by a design change, this will be
performed free of charge. And, you cannot generally fix a problem which
is due to poor design!

Getting into a monitor is usually quite simple requiring the removal of 2-10
Philips or 1/4″ hex head screws – most around the edge of the cabinet or
underneath, a couple perhaps in the rear. Disconnect the input and power
cables first as it they stay with catch on the rear cover you are detaching.
Reconnect whatever is needed for testing after the cover is removed. Set
the screws aside and make notes if they are not all of the same length
and thread type – putting a too long screw in the wrong place can short out
a circuit board or break something else, for example. A screw that is
too short may not be secure.

Once all visible screws are out, try to remove the cover. There still
may be hidden catches or snaps around the edges or seam or hidden beneath
little plastic or rubber cosmetic covers. Sometimes, the tilt-swivel base
will need to be removed first. If no snaps or catches are in evidence,
the cover may just need a bit of persuasion in the form of a carefully
placed screwdriver blade (but be careful not to damage the soft plastic).
A ‘splitting’ tool is actually sold for this purpose.

As you pull the cover straight back (usually) and off, make sure that no
other wires are still attached. Often, the main circuit board rests on
the bottom of the cover in some slots. Go slow as this circuit board may
try to come along with the back. Once the back is off, you may need to prop
the circuit board up with a block of wood to prevent stress damage and contact
with the work surface.

Most – but not all – monitors can be safely and stably positioned either
still on the tilt-swivel base or on the bottom of the frame. However, some
will require care as the circuit board will be vulnerable.

Larger monitors are quite heavy and bulky. Get someone to help and take
precautions if yours is one of the unstable variety. If need be, the monitor
can usually safely be positioned on the CRT face if it is supported by
foam or a folded blanket.

Once the cover is off, you will find anywhere from none to a frustratingly
large number of sheetmetal (perforated or solid) shields. Depending on which
circuit boards need to be accessed, one or more of these shields may need
to be removed. Make notes of which screws go where and store in a safe
place. However, manufacturers often place holes at strategic locations
in order to access adjustments – check for these before going to a lot
of unnecessary bother. Note: sheetmetal usually has sharp edges. Take care.

See Major Parts of Typical SVGA Monitor with Cover
Removed for what will greet you. This particular sample has a shield only
covering the video driver board on the neck of the CRT.

Reassemble in reverse order. Getting the circuit board to slide smoothly
into its slots may take a couple of attempts but otherwise there should
be no surprises.

Specific considerations before poking around inside a TV or monitor

Both electrical and mechanical dangers lurk:

• Main filter capacitor(s). This is the most dangerous (not the HV as you
  would expect). Fortunately, these capacitors will normally discharge in
  a few minutes or less especially if the unit is basically working as the
  load will normally discharge the capacitors nearly fully as power is
  turned off. With TVs, the main filter capacitor is nearly always on the
  mainboard. Monitors are more likely to have a separate power supply
  module.

  However, you should check across this capacitor – usually only one and by
  far the largest in the unit – with a voltmeter and discharge as suggested
  in the section: Safe discharging of capacitors in TVs
  and video monitors if it holds more than a few volts (or wait longer)
  before touching anything.

  Some of these are as large as 1,000 uF charged to 160 V – about 13 w-s or
  a similar amount of energy as that stored in an electronic flash. This is
  enough to be potentially lethal under the wrong circumstances.

• High Voltage capacitor formed by the envelope of the CRT. It is connected
  to the flyback transformer by the fat (usually red) wire at the suction cup
  (well, it looks like one anyhow) attached to the CRT. This capacitor can
  hold a charge for quite a while – weeks in the case of an old tube type TV!

  If you want to be doubly sure, discharge this also. However, unless you
  are going to be removing the HV connector/flyback, it should not bother you.

  The energy stored is about 1 w-s but if you touch it or come near to an
  exposed terminal, due to the high voltage, you will likely be handed *all*
  the energy and you *will* feel it. The danger is probably more in the
  collateral damage when you jump ripping flesh and smashing your head against
  the ceiling.

  Some people calibrate their jump based on voltage – about 1 inch/V. :-).

  There will be some HV on the back of the circuit board on the neck of the
  CRT but although you might receive a tingle but accidentally touching the
  focus or screen (G2) pins, it is not likely to be dangerous.

• CRT implosion risk. Don’t hammer on it. However, it is more likely that
  you will break the neck off the tube since the neck is relatively weak. This
  will ruin your whole day and the TV or monitor but will likely not result in
  flying glass everywhere. Just, don’t go out of your way to find out.
• Sharp sheet metal and so forth. This is not in itself dangerous but
  a reflex reaction can send your flesh into it with nasty consequences.

Dusting out the inside of a monitor

The first thing you will notice when you remove the cover is how super
dusty everything is. Compliments to the maid. You never dreamed there
was that much dust, dirt, and grime, in the entire house or office building!

Use a soft brush (like a new paintbrush) and a vacuum cleaner to carefully
remove the built up dust. Blowing off the dust will likely not hurt the unit
unless it gets redeposited inside various controls or switches but will
be bad for your lungs – and will spread dirt all over the room. Don’t turn
anything – many critical adjustments masquerade as screws that just beg to
be tightened. Resist the impulse for being neat and tidy until you know
exactly what you are doing. Be especially careful around the components on
the neck of the CRT – picture tube – as some of these are easily shifted
in position and control the most dreaded of adjustments – for color purity
and convergence. In particular, there will be a series of adjustable ring
magnets. It is a good idea to mark their position in any case with
some white paint, ‘white out’, or a Magic Marker so that if they do get
moved – or you move them deliberately, you will know where you started.

Troubleshooting a monitor with the mainboard disconnected

There are times when it is desirable to remove the chassis or mainboard and
work on it in a convenient location without having to worry about the
attachments to the CRT and cabinet circuitry.

My approach is usually to do as much work as possible without removing the
main board and not attempt to power it up when disconnected since there are
too many unknowns. Professionals will plug the chassis into a piece of
equipment which will simulate the critical functions but this is rarely
an option for the doit-yourselfer.

Note that if you have a failure of the power supply – blown fuse, startup,
etc., then it should be fine to disconnect the CRT since these problems
are usually totally unrelated. Tests should be valid.

However, if you really want to do live testing with the main board removed,
here are some considerations. There are usually several connections to the
CRT and cabinet:

• Deflection yoke – since the horizontal coils are part of the horizontal
  flyback circuit, there could be problems running without a yoke. This
  could be anything from it appearing totally dead to an overheating or
  blown horizontal output transistor. There may be no problems. Vertical
  and any convergence coils may or may not be problems as well.
• CRT video Driver board – pulling this should not usually affect anything
  except possibly video output and bias voltages.
• CRT 2nd anode – without the CRT, there will be no capacitor to filter
  the high voltage and you would certaily want to insulate the HV connector
  **real** well. I do not know whether there are cases where damage to
  flyback could result from running in thie manner, however.
• Front panel controls – disconnecting these may result in inability to
  even turn the unit on, erratic operation, and other unexpected behavior.
• Degauss – you just won’t have this function when disconnected. But who
  cares – you are not going to be looking at the screen anyhow.
• Remote sensor – no remote control but I doubt that the floating
  signals will cause problems.
• Speakers – there will be no audio but this should not cause damage.

  If you do disconnect everything, make sure to label any connectors whose
  location or orientation may be ambiguous. Most of the time, these will
  only fit one way but not always.

Comments on repairing modern computer monitors

(From: Wild Bill (kwag98@tcis.net).)

Without even taking into consideration all of the other features of
most late model (15″ or larger) monitors, such as the multisync and
multi-resolution circuitry, many of these units are very complex.
They combine almost every example of present circuit design technology.
A vacuum display tube, digital data, HF switching, all types of regulators
and sense circuits and linear power devices. Funny too, that the end result
is just dots of light.

A good (perhaps the best) first action is to search the USENET newsgroup
sci.electronics.repair via
an archive like
Google Groups for
previous postings of questions on the same model with related symptoms and
replies. Solder in the replacement part, and BINGO, it’s repaired. Rest
assured that it’s always something simple. Yeah, right. 🙂 Time to check
some archive repair sites with tech-tips databases.

Typically, for a dead unit, I get a DMM, pencil and paper….

After a fairly thorough overall inspection, i generally resort to a
section-by-section investigation for shorted/open power devices, followed by
PN junction checks, then an overall ESR check SxS.
In circuit ESR checking will nearly always convince me to replace at least a
couple of caps. But if ya don’t replace ’em, ya just never know. Hehehe.

By now, I’m at least an hour into this potential research project, if the
unit’s operation hasn’t yet been restored.
The next phase is usually determined by whatever i feel like doing next.. i
might get a couple of datasheets, try a series lamp technique, or test the
major parts.. flyback/IHVT, CRT or yokes. If one of these are faulty, it
will help determine the cost effectiveness of proceeding. If it’s not my
monitor, i contact the owner.

Barring any major parts failure, there are several more options for a
direction to proceed in.. making sense of any of the available voltages or
waveforms, checking the HV semis for leakage, or as a last (but maybe not
final) resort.. making circuit diagrams of specific sections.
If there hasn’t been any sign of progress by this point, the unit usually
finds it’s way to a shelf until more inspiration arrives.. that reminds me,
when did i place that order?

Monitor Adjustments

These include both controls accessible to the user (and often not understood)
as well as internal adjustments that may need to be touched up due to the
aging of components or following a repair.

Note that monitor (software) drivers often have the capability to provide some
control of picture size, position, color balance, and other parameters via the
video card. There is also third-party software for this purpose. So, before
blaming the monitor, make sure your software settings (and monitor user
controls) have been reset to their defaults. Then see if the monitor
controls and/or the driver adjustments have enough range with the procedures
described below. However, where a sudden change in behavior occurred without
anything being done in either hardware or software (e.g., a new video card or
OS/revision), trying to adjust out such a fault is like putting a Band-Aid on
a broken bone. There is likely to be a hardware fault in the monitor which
will need to be identified and repaired.

User picture adjustment

For general viewing, subdued lighting is preferred. Avoid backlighting
and direct overhead lighting if possible.

Display an image with a variety of colors and the full range of brightness
from deep shadows to strong highlights. For PCs, a Windows desktop is
generally satisfactory. An outdoor scene on a sunny day is excellent for
studio monitors. Alternatively, use a test pattern specially designed
for this purpose.

Turn the BRIGHTNESS and CONTRAST controls (or use the buttons) all the way
down.

Increase the BRIGHTNESS until a raster is just visible in the darkest
(shadow) areas of the picture and then back off until it **just** disappears.

Increase the CONTRAST until the desired intensity of highlights is obtained.

Since BRIGHTNESS and CONTRAST are not always independent, go back and forth
until you get the best picture.

On monitors with a color balance adjustment, you may want to set this but
unless you are doing photorealistic work, using the manufacturer’s defaults
will be fine unless you need to match the characteristics of multiple
monitors located side-by-side.

Focus adjustment

One of the most common complaints is that the monitor is not as crisp as
it used to be – or just not as sharp as expected.

Assuming that the focus has just been gradually getting worse over time,
tweaking the internal focus control may be all that is needed.

Some monitors have the focus adjustment accessible through a (possibly
unmarked) hole in the side or rear of the case. If there is a single
hole, it is almost certainly for overall focus. If there are two holes,
one may be the screen (G2 – master brightness) or the two adjustments may
be for different aspects of focus (e.g., horizontal and vertical). Just
carefully observe what happens when each adjustment is moved a little so
that you can return it to its original setting if you turned the wrong one.
Use a thin insulated screwdriver – preferably with a plastic blade. As
a extra precaution, determine of the screwdriver will mate easily with the
adjustment with the monitor **off** (don’t turn anything, however).

Where there are two adjustment knobs on the flyback transformer, the top one
is generally for focus and the bottom one is for G2.

Most inexpensive monitors have only what is known as static focus – a constant
voltage derived from the HV power supply is applied to the focus grid of the
CRT. This does not allow for optimal focus across the screen and any setting
is just a compromise between central and edge sharpness.

Better monitors will have separate H and V focus controls as well as dynamic
focus circuitry which generates focus correction signals that are a function
of screen position to compensate for changing distance to electron guns at the
edges and corners of the screen. There may be some interaction between the
static and dynamic adjustments. If either of these controls has no effect or
insufficient range, then there may be a fault in the circuitry for that
particular adjustment – a fault with the driver, waveform source, power
supply, etc.

The most sophisticated schemes use a microprocessor (or at least digital
logic) to specify the waveform for each section of the screen with a map of
correction values stored in non-volatile memory. It would be virtually
impossible to troubleshoot these systems without detailed service information
and an oscilloscope – and even then you might need a custom adapter cable and
PC software to adjust values!

Also see the section: About the quality of monitor
focus.

If you need to go inside to tweak focus pots:

SAFETY: as long as you do not go near anything else inside the monitor while
it is on AND keep one hand in you pocket, you should be able to do this without
a shocking experience.

Plug it in, turn it on and let it warm up for a half hour or so. Set your
PC (or other video source) to display in the resolution you use most often.
First turn the user brightness and contrast fully counterclockwise. Turn
brightness up until the raster lines in a totally black area appear, then
back a hair until they disappear. Then, turn the contrast control up until
you get a fairly bright picture. Fullly clockwise is probably ok. Adjust
FOCUS for generally best focus. You will not be able to get it razor sharp
all over the screen – start at the center and then try to get the
edges and corners as good as you can without messing up the center too much.
Double check that the focus is OK at your normal settings of brightness and
contrast and at other resolutions that you normally use.

The focus pot is usually located on the flyback transformer or on an
auxiliary panel nearby. The focus wire usually comes from the flyback or
the general area or from a terminal on a voltage the multiplier module
(if used). It is usually a wire by itself going to the little board
on the neck of the CRT.

The SCREEN control adjusts background brightness. If the two controls are
not marked, you will not do any damage by turning the wrong one – it will
be immediately obvious as the brightness will change rather than focus
and you can then return it to its original position (or refer to the section
on brightness adjustments to optimize its setting).

On a decent monitor, you should be able to make out the individual scanning
lines at all resolutions though it will be toughest at the highest scan rates.
If they lines are fuzzy, especially in bright areas, then focus may need
to be adjusted or there may be an actual fault in the focus circuitry or
a defective or just marginal CRT.

Adjusting Monitors with Dual-Focus Flybacks

(From: Andy Cuffe (baltimora@psu.edu).)

I’m sure there is an official procedure, but this always works for me.

First, figure out which control is which. One will appear affect the
overall focus. This is the vertical focus control.

The other will mostly affect the width of vertical lines and has the
most effect at the left and right edges of the screen. This is the
horizontal focus.

Start with both controls near the middle of their range. You need to
display something with sharp vertical lines at the edges and sharp
horizontal lines in the center (a cross hatch is best).

First, adjust the horizontal focus for the sharpest vertical lines at
the edges. Ignore the thickness of the scan lines for now, just make
the vertical lines are as thin as possible.

Next, adjust the vertical focus for the thinnest horizontal scan lines
in the dead center of the screen. Alternate between the two several
times because they interact with each other heavily.

If you don’t have any way to display a cross hatch, you can use a
computer if it has a TV output, or even the on screen menus of a VCR.

(From: RonKZ650 (RonKZ650@aol.com).)

The old Zeniths with dual focus had a procedure of putting a crosshatch
pattern on the screen, adjust one focus for the thinnest vertical line,
the other for the thinnest horiz line. This works for me on all dual
focus sets. Once you have a crosshatch pattern on the screen it is easy
to see which control effects horiz and which effects vertical. From
there you have to go back and forth between the two a few times to
eventually get both at optimum. I don’t like um, but part of the
business.

Brightness and color balance adjustment

A monitor which has a picture that is too dark or too bright and cannot be
adequately set with the user brightness and contrast controls may need
internal adjustment of the SCREEN (the term, screen, here refers to a
particular electrode inside the CRT, not really the brightness of the screen
you see, though it applies here), MASTER BRIGHTNESS, or BACKGROUND level
controls. As components age, including the CRT, the brightness will
change, usually decrease. The following procedure will not rejuvenate
an old CRT but may get just enough brightness back to provide useful
functionality for a few months or longer. If the problem is not with the age
of the CRT, then it may return the monitor to full brightness. The assumption
here is that there is a picture but the dark areas are totally black and
the light areas are not bright enough even with the user brightness control
turned all the way up.

Note that circuit problems can also cause similar symptoms. These are
particularly likely if the brightness descresed suddenly – CRT emission
problems will result in a gradual decrease in brightness over time.

In most cases, the cover will need to be removed. The controls we
are looking for may be located in various places. Rarely, there will
be access holes on the back or side. However, if there are unmarked
holes, then the FOCUS and SCREEN controls are the most likely possibilities.

The controls may be located on the:

• Flyback (LOPT) transformer. Usually there is a master screen control
  along with a focus control on the flyback transformer.
• A little board on the neck of the CRT. There may be a master screen
  control. a master brightness control, a master background level control,
  or individual controls for red, green, and blue background level. Other
  variations are possible. There may also be individual gain/contrast
  controls.
• Main video board is less common, but the background level controls may
  be located here.

Display a black and white picture at the video resolution you consider most
important. Select one that has both full blacks and full whites – an nice
sunny outdoor scene that has been converted from a color image, for example.

Set the user brightness control to its midpoint and the user contrast
control as low as it will go – counterclockwise.

Let the monitor warm up for at least 15 minutes so that components can
stabilize.

If there is a MASTER BRIGHTNESS or BACKGROUND level control, use this to
make the black areas of the picture just barely disappear. Them, increase
it until the raster lines just appear. (They should be a neutral gray.
If there is a color tint present, then the individual color background
controls will need to be adjusted to obtain a neutral gray.) If there is no
such control, use the master screen control on the flyback. If it is unmarked,
then try both of the controls on the flyback – one will be the screen control
and the other will be focus – the effects will be obvious. If you did touch
focus, set it for best overall focus and then get back to the section on focus
once you are done here.

If there are individual controls for each color, you may use these but be
careful as you will be effecting the color balance. Adjust so that the
raster lines in a black area are just visible and dark neutral gray.

If there is a ‘service switch’ you may prefer to make the adjustment
with this in the service position. The raster will collapse to a single
horizontal line and the video input will be disabled and forced to black.
The BACKGROUND or SCREEN control can then be adjusted as above.

Now for the gain controls. On the little board on the neck of the CRT
or on the video or main board there will be controls for R, G, and B DRIVE
(also may be called GAIN, or CONTRAST – they are the same). The knobs or
slots may even be color coded as to which primary (R,G,B) it affects.

If there are only two then the third color is fixed and if the color balance
in the highlights of the picture was ok, then there is nothing more you can
do here.

Set the user contrast control as high as it will go – clockwise.

Now adjust each internal color DRIVE control as high as you can without
that particular color ‘blooming’ at very bright vertical edges. Blooming
means that the focus deteriorates for that color and you get a big blotch
of color trailing off to the right of the edge. You may need to go back
and forth among the 3 DRIVE controls since the color that blooms first
will limit the amount that you can increase the contrast settings. Set
them so that you get the brightest neutral whites possible without any
single color blooming.

Note that this is ignoring the effects of any beam current or brightness
limiter circuitry. Any recommendations in the service manual should be
followed to minimize the chance of excess X-ray emissions as well as to
avoid burn-in of the phosphor screen.

Now check out the range of the user controls and adjust the appropriate
internal controls where necessary. You may need to touch up the background
levels or other settings. Check at the other resolutions and refresh rates
that you normally use.

If none of this provides acceptable brightness, then either your CRT
is in its twilight years or there is something actually broken in the
monitor. If the decrease in brightness has been a gradual process over the
course of years, then it is most likely the CRT. As a last resort you can
try increasing the filament current to the CRT the way CRT boosters that
used to be sold for TVs worked. See the section:
Brightening an old CRT.

Optimal procedure for setting brightness/background and screen adjustments

For slight tweaks, the following is not necessary. However, if someone
turned all the internal controls, if you are making significant changes
that affect G2 (screen), or you are setting up a new or replacement CRT for
the first time, then following the procedure below is desirable to achieve
best performance and maximize life of the CRT.

The typical user controls – brightness and contrast can, of course, be set
arbitrarily, depending on video content and ambient lighting conditions.

Set the user brightness and contrast controls in the middle for the following
adjustments and let the monitor warm up for 20 minutes or so.

(From: Jeroen Stessen (Jeroen.Stessen@philips.com).)

Now the screen control, that’s another matter. It sets the voltage
on the second grid of the electron guns, typically between +500 and
+1000 V. You will want to use a well-isolated screwdriver for that
if it is a naked potentiometer. In the old days there used to be 3
separate potentiometers for 3 G2s, now there is generally only one.

Its purpose is to set the cutoff voltage for the guns, i.e. the
voltage between K and G1 at which the beam is just off. The higher
you set the VG2, the higher VK – VG1 must be to cut off the beam.

If you set VG2 too low then your picture will be dark. You can
compensate for that with the brightness control, which in effect will
lower the VKs. A disadvantage is that you will not get optimum
sharpness and peak brightness from your picture tube.

If you set VG2 too high then your picture will be bright. You can
compensate for that with the brightness control, which in effect will
raise the VKs. You might even get retrace lines which can usually
not be made to disappear with the brightness control. Another
disadvantage is that you will not get optimum LIFETIME from your
picture tube. With a too high cutoff voltage the cathode (electron
emitting surface) will wear out too soon.

You will need to see the picture tube specifications (or possibly
the service manual for the monitor — sam) in order to find the correct
setting for the cutoff voltage. This is measured as VK – VG1 (for each
channel RGB) and is typically 130-160 V max. There will be spread between
the 3 channels, typically the highest of the 3 measured values will be set
against the upper limit.

The usual adjustment procedure is as follows:

• Use any low-level adjustments to set a black picture with all 3
  cathode voltages at the specified level (e.g. 130 V) above
  the VG1 voltage (may be 0 V or 12 V or 20 V ?). (These are typically
  called RGB brightness, bias, or background level and are often on the
  little board on the neck of the CRT but not always — sam).
• Adjust VG2 (screen) until one colour just starts too light up,
  turn it back down until the screen is just black again. (Occasionally,
  there are two G2 controls – one on the flyback and another on the CRT neck
  board or elsewhere. If so, they control are basically in series – leave
  the one on the flyback alone if the other one has enough range.)
• Now adjust 2 of the 3 low-level black controls until the
  other 2 colours just light up, and then back to black again.
• Select a white picture and use 2 low-level white (RGB drive or gain, also
  generally on the neck board — sam) controls to set the proper colour
  temperature for white to your own taste.
• Check your black calibration again, may have to iterate a bit.

Position, size, and linearity adjustment

Position and size are usually user controls on computer and video monitors
but not on TVs. On monitors with digital controls, they may usually be set
for each resolution and (automatically) stored in non-volatile memory so they
will be retained when the monitor is turned off. On cheaper monitors, there
may be a knobs on the front or back panel and may need to readjusted whenever
the scan rate/resolution is changed. Sometimes, there are located internally.
There may be separate adjustments for each scan range and may or may not be
accessible through holes in the back panel.

There may also be an adjustment called ‘horizontal phase’ which controls the
relative timing of the horizontal sync pulse with respect to retrace. Its
effect is subtly different than horizontal position which actually moves the
raster. If possible, center the raster and then use H Phase to center the
picture.

In monochrome monitors (mostly), position may be set via a pair of rings on the
neck of the CRT.

Size can be set to your preference for each scan rate (if they are
independent). For computer work, slight underscan is often preferred as
all of the frame buffer is visible. However, any slight geometric problems
with the raster will be all too visible when compared with the straight
sides of the CRT bezel.

Note that resolutions like 640 x 480, 800 x 600, and 1024 x 768 all have a
4:3 aspect ratio. The edge of the image will line up with the bezel on most
if not all monitors since CRTs are made to a 4:3 aspect ratio. However,
resolutions like 1280 x 1024 and 1600 x 1280 have a 5:4 aspect ratio. With
these, in order to get (highly desirable) square pixels, the horizontal size
must be adjusted slightly smaller than that required to fill the screen.

For normal viewing of video (television) monitors, raster size should be set
so that there is about 10-15 percent overscan all around. This will allow
ample margin for power line voltage fluctuations, component aging, and the
reduction in raster size that may occur with some VCR special effects (CUE and
REV) modes. However, for studio use, underscan is often preferred or at least
an option to permit the entire raster to be inspected.

Modern color monitors may not have any horizontal linearity control but you
may find this on older models. There may be an internal vertical linearity
adjustment. I am not aware of any that have user accessible linearity
controls. If there are internal pots or coils, you will need to go back
and forth between size and linearity as these adjustments are usually not
independent.

Of course, parameters controlling your video card also affect position and
size. There is no best approach to reconciling the effects of monitor and
video card position adjustments. But, in general, start with the monitor
controls centered within their range or use the memory defaults as
appropriate. Then, use the video card setup program to optimize the
settings. Only if these do not have enough range should you use the
monitor controls.

Comments on linearity or lack thereof

(From: Jerry Greenberg (jerryg50@hotmail.com).)

If you can get a grating test generator this would be the proper way
to test for non-linearity. Using a camera or device other than that
would not be an acceptable reference if you call any engineer from the
manufacture. If you mention a grating generator, he will certainly
listen.

You would need the service manual for the model to know the specs. Some of
these sets can have a non-linearity of up to about 2% near to the edges. Only
professional broadcast monitors will be down to the 0.5% and less error factor
near to the corners.

On a 27 inch screen 2% can mean an error of can give a visible non-linearity
of 0.5 inches. Convergence errors can be as much as 0.25 or 1/4 inch at the
corners. Generally they are more accurate than these figures. This is the
worse case that is generally accepted on a consumer TV by the manufactures.

I have found that on flat screen consumer TV sets, the linearity sort of gets
a bit stretched towards the ends of the scan. This is because of the beam
angle. There is compensation for azimuth of beam focus (dynamic focus) and
for the scans to a degree that keeps the price of the TV within consumer
range.

The screens that are a bit more spherical or rounded will have less of this
effect because it is lower in cost to compensate for these errors. A true
accurate screen would be one that is spherical following exactly to the beam
angle. But, for viewing this would not be very desirable.

Pincushion adjustments

Horizontal pincushion refers to any bowing in or out on the vertical sides of
the raster. There is not usually any explicit vertical pincushion adjustment.
Adjustment usually uses two controls – amplitude and phase. Pincushion
amplitude as its name implies, controls the size of the correction. Pincushion
phase affects where on the sides it is applied. Don’t expect perfection.

If the controls have no effect, there is probably a fault in the pincushion
correction circuitry.

It is best to make these adjustments with a crosshatch or dot test pattern

Geometry adjustment

This refers to imperfections in the shape of the picture not handled
by the pincushion and size adjustments. These types of defects include a
trapezoidal or keystone shaped raster and jogs or wiggles around the periphery
of the raster. Unfortunately, one way these are handled at the factory is to
glue little magnets to strategic locations on the CRT and/or rotate little
magnets mounted on the yoke frame. Unless you really cannot live with the
way it is (assuming there isn’t something actually broken), leave these
alone! You can end up with worse problems. In any case, carefully mark the
position AND orientation of every magnet so that if this happens, you can
get back to where you started. If the magnets are on little swivels, some
experimenting with them one at a time may result in some improvement. Of
course it is best to obtain a service manual and follow its instructions.
However, this may not be possible at reasonable cost or at all for many
computer monitors.

Why is the convergence on my monitor bad near the edges

Very simple – nothing is quite perfect. Perfect convergence is not
even necessarily possible in theory with the set of adjustments available
on a typical monitor. It is all a matter of compromises. Consider what
you are trying to do: get three electron beams which originate from
different electron guns to meet at a single point within a fraction
of a mm everywhere on the screen. This while the beams are scanning
at an typical effective writing rate of 50,000 mph across the face of a 17″
CRT (assumed resolution: 1024×768 at 75 Hz) in a variable magnetic environment
manufactured at a price you can afford without a second mortgage!

The specifications for misconvergence have two parts: a center error and a
corner error. The acceptable center error is always the smaller of the
two – possibly .1-.2 mm. compared to .3-.5 mm in the corners. Very often,
you will find that what you are complaining about is well within this
specification.

CRT purity and convergence

Purity assures that each of the beams for the 3 primary colors – R, G, B, –
red, green, and blue – strikes only the proper phosphor for that color. A
totally red scene will appear pure red and so forth. Symptoms of poor purity
are blotches of discoloration on the screen. Objects will change shades of
color when the move from one part of the screen to another. There may even be
excess non-uniformity of pure white or gray images.

Convergence refers to the control of the instantaneous positions of the red,
green, and blue spots as they scan across the face of the CRT so that they are
as nearly coincident as possible. Symptoms of poor convergence are colored
borders on solid objects or visible separate R, G, and B images of fine lines
or images,

Note: It is probably best to face the monitor East-West (front-to-back) when
performing any purity and convergence adjustments. Since you probably do not
know what orientation will eventually be used, this is the best compromise as
the earth’s magnetic field will be aligned mostly across the CRT. This will
minimize the possible rotation of the picture when the unit is moved to its
final position but there may be a position shift. Neither of these is that
significant so it probably doesn’t really matter that much unless you are
super fussy. Of course, if you know the final orientation of the monitor use
that instead. Or, plan to do the final tilt and position adjustments after
the monitor is in position – but this will probably require access to the
inside!

First, make sure no sources of strong magnetic fields are in the vicinity of
the monitor – loudspeakers, refrigerator magnets, MRI scanners, etc. A nearby
lightning strike or EMP from a nuclear explosion can also affect purity
so try to avoid these.

Cycle power a couple of times to degauss the CRT (1 minute on, 20 minutes
off) – see the section: Degaussing (demagnetizing) a
CRT. If the built in degaussing circuits have no effect, use an external
manual degaussing coil to be sure that your problems are not simply due to
residual magnetism.

Assuming this doesn’t help, you will need to set the internal purity
and/or convergence adjustments on the CRT.

First, mark the positions of all adjustments – use white paint, ‘White out’,
or a Magic Marker on the ring magnets on the neck of the CRT, the position
and tilt of the deflection yoke, and any other controls that you may touch
deliberately or by accident.

Note: if your monitor is still of the type with a drawer or panel of knobs
for these adjustments, don’t even think about doing anything without a
service manual and follow it to the letter unless the functions of all
the knobs is clearly marked (some manufacturers actually do a pretty good
job of this).

CRT purity adjustment

Purity on modern CRTs is usually set by a combination of a set of ring
magnets just behind the deflection yoke on the neck of the CRT and the
position of the yoke fore-aft. As always, mark the starting position of
all the rings and make sure you are adjusting the correct set if rings!

Use the following purity adjustment procedure as a general guide only.
Depending on the particular model monitor, your procedure may substitute
green for red depending on the arrangement of guns in the CRT. The procedures
for dot-mask, slot mask, and Trinitron (aperture grille) CRTs will vary
slightly. See you service manual!

Obtain a white raster (sometimes there is a test point that can be grounded
to force this). Then, turn down the bias controls for blue and green so
that you have a pure red raster. Let the monitor warm up for a minimum of
15 minutes.

Loosen the deflection yoke clamp and move the yoke as far back as it will go,

Adjust the purity magnets to center the red vertical raster on the screen.

Now, move the yoke forward until you have the best overall red purity.
Tighten the clamp securely and reinstall the rubber wedges (if your CRT
has these) to stabilize the yoke position. Reset the video adjustments
you touched to get a red raster.

CRT convergence adjustment

In the good old days when monitors were monitors (and not just a mass
produced commodity item) there were literally drawers or panels full of
knobs for setting convergence. One could spend hours and still end up
with a less than satisfactory picture. As the technology progressed,
the number of electronic adjustments went down drastically so that today
there are very few if any. However, some high end monitors do have user
accessible controls for minor adjustment of static (center) convergence.

Unless you want a lot of frustration, I would recommend not messing with
convergence. You could end up a lot worse. I have no idea what is used
for convergence on your set but convergence adjustments are never
quite independent of one another. You could find an adjustment that
fixes the problem you think you have only to discover some other area
of the screen is totally screwed. In addition, there are adjustments
for geometry and purity and maybe others that you may accidentally move
without even knowing it until you have buttoned up the set.

Warning: Accurately mark the original positions – sometimes you will change
something that will not have an obvious effect but will be noticeable
later on. So it is extremely important to be able to get back to where
you started. If only red/green vertical lines are offset, then it is
likely that only a single ring needs to be moved – and by just a hair.
But, you may accidentally move something else!

If you really cannot live with it, make sure you mark everything very
carefully so you can get back to your current state. A service manual is
essential!

Convergence is set using a white crosshatch or dot test pattern. For PCs
(a similar approach applies to workstations) If you do not have a test
pattern generator, use a program like Windows Paint to create a facsimile
of a crosshatch pattern and use this for your convergence adjustments.
For a studio video monitor, any static scene (from a camcorder
or previously recorded tape, for example) with a lot of fine detail will
suffice.

Static convergence sets the beams to be coincident in the exact center of
the screen. This is done using a set of ring magnets behind the purity
magnets on the CRT neck. (Set any user convergence controls to their
center position).

Adjust the center set of magnets on the CRT neck to converge blue to green
at the center of the screen. Adjust the rear set of magnets to converge
red to green at the center of the screen.” Your monitor may have a slightly
different procedure.

Dynamic convergence adjusts for coincidence at the edges and corners.

On old tube, hybrid, and early solid state monitors, dynamic convergence was
accomplished with electronic adjustments of which there may have been
a dozen or more that were not independent. With modern monitors, convergence
is done with magnet rings on the neck of the CRT, magnets glued to the CRT,
and by tilting the deflection yoke. The clamp in conjunction with rubber
wedges or set screws assures that the yoke remains in position.

Remove the rubber wedges.

Loosen the deflection yoke clamp just enough so that it can be tilted but
will remain in the position you leave it. Rock the yoke up and down to
converge the right and left sides of the screen. Rock the yoke from side
to side to converge the top and bottom of the screen. The rubber wedges
can be used as pivots to minimize the interaction between the two axes but
you may need to go back and forth to optimize convergence on all sides.
Reinstall the wedges firmly and tape them to the CRT securely. Tighten the
yoke clamp enough to prevent accidental movement.

Some monitors may use a plastic frame and set screws instead of just a clamp
and rubber wedges but the procedure is similar.

Refer to your service manual. (Is this beginning to sound repetitious?)

For additional comments on convergence adjustments, see the section:
Tony’s notes on setting convergence on older delta
gun CRTs.

Tilted picture

You have just noticed that the picture on your fancy (or cheap) monitor is not
quite horizontal – not aligned with the front bezel. Note that often there is
some keystoning or other geometric distortion as well where the top and bottom
or left and right edges of the picture are not quite parallel – which you may
never have noticed until now. Since this may not be correctable (at least,
not without a lot of hassle), adjusting tilt may represent a compromise at
best between top/bottom or left/right alignment of the picture edges. You
may never sleep again knowing that your monitor picture is not perfect! BTW,
I can sympathize with your unhappiness. Few things are more annoying than a
just noticeable imperfection such as this.

This is probably one reason why older monitors tended not to be able to expand
the picture to totally fill the screen – it is easier to overlook imperfect
picture geometry if there is black space between the edges of the picture and
the bezel!

There are several possible causes for a tilted picture:

1. Monitor orientation. The horizontal component of the earth’s magnetic field
   affects this slightly. Therefore, if you rotate the unit you may be able
   to correct the tilt. Of course, it will probably want to face the wall!
2. Other external magnetic fields can sometimes cause a rotation without any
   other obvious effects – have you changed the monitor’s location? Did an
   MRI scanner move in next door?
3. Need for degaussing. Most of the time, magnetization of the CRT will
   result in color problems which will be far more obvious than a slight
   rotation. However, internal or external shields or other metal parts in
   the monitor could become magnetized resulting a tilt. More extensive
   treatment than provided by the built-in degaussing coil may be needed.
   Even, the normal manual degaussing procedure may not be enough to get close
   enough to all the affected parts.
4. You just became aware of it but nothing has changed. Don’t dismiss this
   offhand. It is amazing how much we ignore unless it is brought to our
   attention. Are you a perfectionist? Did your friend just visit boasting
   about his P8-1000 screamer and point the tilt out to you?
5. There is an external tilt control which may be misadjusted. Newer Sony
   monitors have this (don’t know about TVs) – a most wonderful addition.
   Too bad about the stabilizing wires on Trinitron CRTs. A digital control
   may have lost its memory accidentally. The circuitry could have a problem.

   For example, on the Sony CPD1730, you press the left arrow button and blue
   ‘+’ button at the same time. Then adjust the tilt with the red buttons.

6. There is an internal tilt control that is misadjusted or not functioning.
   The existence of such a control is becoming more common.
7. The deflection yoke on the CRT has gotten rotated or was not oriented
   correctly at the time of the set’s manufacture. Sometimes, the entire yoke
   is glued in place in addition to being clamped adding another complication.

   If the monitor was recently bumped or handled roughly, the yoke may have
   been knocked out of position. But in most cases, the amount of abuse
   required to do this with the yoke firmly clamped and/or glued would have
   totally destroyed it in the process.

   There is a risk (in addition to the risk of frying yourself on the various
   voltages present inside an operating monitor) of messing up the convergence
   or purity when fiddling with the yoke or anything around it since the yoke
   position on the neck of the tube and its tilt may affect purity and
   convergence. Tape any rubber wedges under the yoke securely in place
   as these will maintain the proper position and tilt of the yoke while you
   are messing with it. (Don’t assume the existing tape will hold – the
   adhesive is probably dry and brittle).

8. The CRT may have rotated slightly with respect to the front bezel.
   Irrespective of the cause of the tilt, sometimes it is possible to
   loosen the 4 (typical) CRT mounting screws and correct the tilt by
   slightly rotating the CRT. This may be easier than rotating the yoke.
   Just make sure to take proper safety precautions when reaching inside!

Monochrome monitor size, position, and geometry adjustments

These tend to be a lot simpler and less critical than for color monitors
or TV sets.

On a monochrome (B/W) monitor you will probably see some of the following
adjustments:

1. Position – a pair of rings with tabs on the neck of the CRT.
   There may be electronic position adjustements as well.
2. Width and height (possibly linearity as well) controls. There may be
   some interaction between size and linearity – a crosshatch test pattern
   is best for this. Vertical adjustments are almost always pots while
   horizontal (if they exist) may be pots and/or coils. Where desired,
   set sizes for 5-10% overscan to account for line voltage fluctuations and
   component drift. Confirm aspect ratio with test pattern which includes
   square boxes.
3. Geometry – some little magnets either on swivels around the yoke or
   glued to the CRT. If these shifted, the the edges may have gotten
   messed up – wiggles, dips, concave or convex shapes. There may be
   a doxen or more each mostly affecting a region around the edge of the
   raster. However, they will not be totally independent.

Check at extremes of brightness/contrast as there may be some slight
changes in size and position due to imperfect HV regulation.

There may be others as well but without a service manual, there is no
way of knowing for sure.

Just mark everything carefully before changing – then you will be able to
get back where you started.

Low Voltage Power Supply Problems

Low voltage power supply fundamentals

Monitors require a variety of voltages (at various power levels) to function.
The function of the low voltage power supply is to take the AC line input
of either 115 VAC 60 Hz (220 to 240 VAC 50 Hz or other AC power in Europe and
elsewhere) and produce some of these DC voltages.

Typical Switchmode Power Supply for Small SVGA Color
Monitor shows the complete schematic for the SMPS from a “I guarantee you
never heard of the brand name” monitor.

The AC line input and degauss components are at the upper left, the SMPS
chopper, its controller, and feedback opto-isolator are lower left/middle,
and the secondaries – some with additional regulation components – occupy the
entire right side of this diagram. Even for relatively basic application such
as this, the circuitry is quite complex. There are more than a half dozen
separate outputs regulated in at least 3 different ways!

For large high performance auto-scan monitors, it becomes even worse as highly
stable voltages need to be programmed based on a wide range of scan rates.
Several common design approaches are used to generate the required variable
regulated B+ voltage:

1. A separate programmable SMPS generates the B+. This is done by selecting
   its reference voltage or the fraction of the output voltage that is fed
   back to the regulator.
2. A voltage from the main SMPS is fed through an additional series switchmode
   or linear regulator that drops it down to the required value.
3. One of several fixed post-regulators is selected based on scan rate.

Technique (2) is used by the power supply is the diagram, above. Can you
locate the circuitry? Hint: Look in the upper right hand corner of the
schematic.

The need for a variable B+ is one area where a typical PC monitor departs
significantly in design compared to a TV or fixed scan rate studio or
workstation monitor. Nearly everything is made more complex as a result of
this requirement.

Components of the low voltage power supply

All monitor low voltage power supplies will have:

1. A power switch, relay, or triac to enable main power.
2. Various line filter, RFI, and surge suppression components (coupled
   inductors, LCL filter networks, MOVs, etc.).
3. A set of rectifiers – usually in a bridge or doubler configuration – to
   turn the AC into DC. Additional small ceramic capacitors are normally
   placed across the diodes to reduce RF interference. There may be an
   inrush current limiter in the form of an NTC (Negative Temperature
   Coefficient) resistor.
4. One or more large filter capacitors to smooth the unregulated DC. This
   voltage is either around 300 to 320 VDC (doubled from 115 VAC or bridge
   rectified from 230 VAC) for compatibility with U.S. and foreign power or
   150 to 160 VDC bridge rectifier from the 115 VAC line.

   Many monitors permit the input voltage to be either 115 or 230 VAC
   depending on a switch or jumper, or automatically adapt to these or a
   range of input voltages – usually 100 to 240 VAC or DC. The latter are
   termed ‘universal’ power supplies.

5. A discrete, hybrid, IC, or switchmode regulator to provide B+ to the
   horizontal deflection.
6. Some means of generating the various other DC voltages required by the
   monitor’s analog and logic circuitry.

Items (1) to (6) may be part of a separate low voltage power supply module
or located on the mainboard.

7. Zero or more voltage dividers and/or regulators to produce additional
   voltages directly from the line power. This relatively rare except for
   startup circuits. THESE VOLTAGES WILL NOT BE ISOLATED FROM THE AC LINE!
8. A degauss control circuit usually including a thermistor or Posistor
   (a combination of a heater disk and Positive Temperature Coefficient (PTC)
   thermistor in a single package). Monitors having manual degauss buttons
   will include additional circuitry.
9. A startup circuit for booting the horizontal deflection if various
   voltages to run the monitor are derived from the flyback. This may be an
   IC, discrete multivibrator, or something else running off a non-isolated
   voltage or the standby power supply, or it may be derived from the video
   input. (Mostly small video monitors, not autoscan types.) However, the
   SMPS itself will have a startup circuit!
10. A standby power supply if the monitor doesn’t use a latching power switch.
    Usually, this is a separate low voltage power supply using a small power
    transformer for line isolation.

What symptoms are likely the result of a low voltage power supply problem?

There are an almost unlimited number of possibilities but the following
probably covers the most likely:

• Monitor is as dead as a concrete block – no picture or raster, no LEDs lit,
  no sounds of life (like degauss) of any kind.

  Most likely causes: No power at AC outlet or outlet strip, bad or loose line
  cord, bad power switch, blown fuse due to internal short or overload.

• No picture but unusual sounds like a whine, periodic clicks, tweets, or
  flubs, and/or possibly flickering or flashing front panel LEDs.

  Most likely causes: Excessive load or short on output of power supply
  (shutdown or cycling due to overcurrent) or loss of horizontal drive
  (cycling from overvoltage due to lack of load).

• Unusual aromas, smoke, or six foot flames coming from inside the case.

  Most likely causes: Failed parts in low voltage power supply, deflection,
  or high voltage sections.

  Actually, while burning smells and even smoke aren’t that unusual when parts
  overheat as a result of a short circuit, actual fire is quite unlikely due
  to regulatory design requirements for materials and protection devices
  UNLESS safety systems have been tampered with or the monitor has been
  operated in an environment where there is lots of flammable dust.

• Jittering, vibrating, or unstable picture.

  Most likely causes: External magnetic interference or power line
  noise, hum in various power supply voltages resulting from dried up main
  filter capacitor(s) or other capacitors, resistors out of tolerance – all
  affecting power supply regulation.

• Loss of video, deflection, geometry or size problems, or some or all
  adjustments have no effect.

  Most likely causes: Failure of one or more power supply voltages, selection
  circuitry not selecting properly (autoscan monitors), bad connections.

• Monitor doesn’t power up immediately.

  Most likely causes: Dried up electrolytic capacitors in power supply or bad
  connections.

• Interaction of adjustments. For example, turning up the brightness results
  in a loss of sync or a wavy raster.

  Most likely causes: Poor power supply regulation due to bad capacitor,
  resistor, regulator, or other component – or bad connections.

Note that the underlying cause may not be in the low voltage power supply
itself but may actually be elsewhere – a shorted horizontal output transistor
or deflection yoke, for example. This results in either the power supply
shutting down, becoming extremely unhappy, blowing a fuse, or just plain
dying. Thus, we cannot really limit our investigation to only the power
supply! In fact, with so many interconnected systems in a monitor,
particularly a high performance SVGA model – it can require the services of
a master sleuth Sherlock Holmes type to identify the perpetrator!

However, before you break out the socket wrenches and DMM (or 10 pound
hammer!) or call Scotland Yard, double check that:

• your AC outlet is live, the power cord is intact (not chewed by the dog),
  is firmly seated, and the monitor is switched on.
• that you have a valid video signal, the video cables are securely attached
  to the proper connectors (e.g., BNCs) and/or there are no bent over pins
  (e.g., VGA/SVGA HD15 or Mac DB15).
• the monitor isn’t being commanded to go into a power savings mode because
  your computer thinks it is smarter than you!
• you have the front panel switches and controls set properly and the video
  source selection is correct. Reset it to factory defaults.

If possible, try the monitor with another known good video input that is
compatible with its scan rates and signal levels or substitute a known
good monitor for the suspect unit. In other words, try to rule out external
problems and ‘cockpit error’.

Monitor power supply problems

WARNING: Always use an isolation transformer when working on a monitor but
this is especially important – for your safety – when dealing with the
non-isolated line operated power supply section. Read and follow the safety
guidelines presented last month and at my Web site.

The following can cause symptoms of a dead or mostly dead monitor:

1. Shorted Horizontal output transistor (HOT). This will usually blow a fuse
   or fusable resistor as well if fed directly from the AC line. However,
   when fed by a SMPS, the result may just be a soft audible whine or periodic
   tweet or flub possibly accompanied by flashing front panel LEDs. Here, the
   failure is not in the power supply itself but may result in damage to it
   or other components especially if it continues to run in this state.
2. Shorted output rectifier diodes can load down the outputs to the point of
   shutting down or resulting in the same audible symptoms as (1) above.
3. Flyback transformer can have shorted windings or shorts in the focus/screen
   divider network which load down the output.

   These (primary shorts in particular) may cause the horizontal output
   transistor to fail as well. This is a common problem with older MacIntosh
   computers and video terminals. Some secondary faults may not be instantly
   destructive but result in little or no high voltage and eventual
   overheating.

4. Some load or even the CRT could be shorted leading similar behavior or
   blowing fuses or fusable resistors which then result in no power to that
   circuitry.
5. Failure in horizontal drive chain – horizontal oscillator, driver, or
   driver transformer. Newer monitors may use an IC for the oscillator and
   this can fail. Without drive, there will be no deflection and this will
   either result in no high voltage directly (when it is derived from the
   horizontal deflection) or cause it to be shut down to prevent CRT screen
   burn (from a stationary spot or line). When powered by an SMPS, there may
   be an audible ticking from the SMPS cycling on overvoltage due to lack of
   load. This is also not a failure of the power supply itself.
6. Failure of an SMPS to start. There can be any number of causes though
   dried up electrolytic capacitors and open high value startup resistors are
   high on the list if the chopper transistor is not blown.
7. Cold solder joints or other bad connections – monitors tend to have these
   as a result of temperature cycling and with all too many – poor manufacturing
   quality control. It is possible that no parts have been damaged – at least
   not yet. Resoldering may be all that is needed.

If there is B+ (typically 60 to 150 VDC depending on the scan rate) at the
output of the power supply but nothing on the HOT collector, an open fusable
resistor, blown fuse, or bad connection, is likely.

If there is voltage on the HOT collector, there is probably a drive problem.

Troubleshooting the switchmode power supply

If the SMPS is a separate module, it may be possible to unplug its output
connector and test it for proper operation independently of the monitor
circuitry. However, a minimum load may be needed at least on the output
that is used for regulation feedback and there could be other interlocks
that will complicate your testing.

The most common failures in monitor SMPSs are:

• Main chopper transistor – in a monitor, this is often an expensive power
  MOSFET.
• Other shorted semiconductors – particularly high speed rectifiers on
  the secondary side of the high frequency transformer.
• Dried up electrolytic capacitors leading to startup and regulation
  problems.
• Open high value startup resistors resulting in no initial drive to chopper.
• Bad connections (is this sounding repetitive?).

See the document: Notes on the Troubleshooting and
Repair of Small Switchmode Power Supplies for more information.

Common problems

Here are just a few of those that you may come across:

Power button on monitor is flakey

If the on/off (or other button) on the monitor itself behaves erratically
then the most likely cause is the obvious – the button or switch is dirty
or worn. Believe it or not, this isn’t as unusual as you might think On a
momentary pushbutton, if you can get at it, some contact cleaner may help.
Replacement with a common pushbutton or toggle type switch (as appropriate)
available at Radio Shack may be much easier than attempting to locate the
original part!

Dead monitor

This means that there is absolutely no evidence of anything happening when
the power switch is activated.

The most like causes are:

• Outlet isn’t live, power cord is loose or defective. Try something else in
  the outlet, inspect/replace the power cord.
• Bad power switch. With plug pulled, check for continuity in the on or
  pressed position.
• Blown fuse or fusable resistor (probably from shorted parts in power supply
  or elsewhere like the HOT). It usually won’t hurt to try a replacement fuse
  with exactly the same ratings but don’t be surprised if it blows.
• Bad power supply (not starting up or just dead), bad connections. However,
  degauss would likely still operate in this case.

Monitor blows fuse

A blown fuse is a very common type of fault due to poor design very often
triggered by power surges due to outages or lightning storms. However,
the most likely parts to short are easily tested, usually in-circuit, with
an ohmmeter and then easily removed to confirm.

Note that it *may be* useful to replace a fuse the *first* time it blows
(though it would be better to do some basic checks for shorted components
first as there is a small chance that having a fuse blow the second time could
result in additional damage which would further complicate the troubleshooting
process). However, if the new one blows, there is a real problem and the only
use in feeding the TV fuses will be to keep the fuse manufacturer in business!

Sometimes, a fuse will just die of old age or be zapped by a power surge that
caused no damage to the rest of the monitor. However, it must be an EXACT
replacement (including slo-blow if that is what was there originally). Else,
there could be safety issues (e.g., fire hazard or equipment damage from too
large a current rating) or you could be chasing a non-existent problem
(e.g., if the new fuse is not slo-blow and is blown by the degauss circuit
inrush current but nothing is actually wrong).

If the fuse blows absolutely instantly with no indication that the circuits
are functioning (no high pitched horizontal deflection whine (if your dog
hides under the couch whenever the monitor is turned on, something is probably
working).) then this points to a short somewhere quite near the AC power
input. However, if there is indication of life – for a second or two, or
longer, and then the fuse blows, the cause is likely an overload on the
power supply. See the section: Dead monitor with
audible whine, periodic tweet or flub, and low-low voltage since
similar causes apply.

For the instantly blown fuse case, the most common places to look would be:

• Degauss Posistor. This is a combination of a heater and PTC thermistor
  which controls current to the degauss coil upon power-on. These tend to
  like to turn into short circuits.
• Shorted parts in the AC input line filter caps and MOVs.
• Diode(s) in main bridge.
• Main filter capacitor(s).
• SMPS chopper (usually a MOSFET) if there is a line operated SMPS or
  HOT (if a deflection derived power supply).

You should be able to eliminate these one by one using a multimeter to
check for short circuits/low resistance. It is best to remove at least one
side of each component while testing to avoid sneak paths which can fool
your meter.

WARNING: Make sure to unplug the monitor and discharge the main filter
capacitor(s) before attempting any of the following measuremente!

Unplug the degauss coil as this will show up as a low resistance.

• Measure across the input to the main power rectifiers – the resistance
  should not be that low (though it may start out at zero and climb as the
  main filter capacitors charge). A reading of only a few ohms may mean a
  shorted rectifier or two, a shorted Posistor, or a fried MOV.
• Test the posistor (if present). Trace back from the degauss connector – it
  will probably be nearby. The posistor is a little cubical component (about
  1/2″ x 3/4″ x 1″) with 3 legs. It includes a line operated heater disk
  (which often shorts out) and a PTC (Positive Temperature Coefficient)
  thermistor to control current to the degauss coil. The easiest thing to do
  it so remove the posistor and try power. If the monitor now works, obtain a
  replacement but in the meantime you just won’t have the automatic degauss.
• Remove and test the HOT or chopper with an ohmmeter. A reading of less
  than 10 ohms between any combination of pins means the device is shorted.

For everything but the HOT or chopper, replacing the bad parts should
be all that is needed – these rarely fail due to OTHER parts going bad.

However, if the HOT or chopper tests bad, it is possible (though not always
the case) that something downstream is causing an excessive load which caused
the part to fail. Therefore, don’t put the cover back on just yet!

With the HOT or chopper removed, it should be possible to power the monitor
with your series light bulb. Of course, not much will work – surprise,
surprise. 🙂 With the deguass coil unplugged, the light should flash once as
the main filter caps charge and then remain dark.

WARNING: Unplug the monitor and discharge the main filter caps after trying
this experiment!

Install a new transistor and power the monitor using your series light bulb.

• If the bulb now flashes once and then settles down to a low brightness
  level, the monitor may be fine. See if there is an indication of deflection
  and HV – look for the glow of the CRT filaments and turn up the brightness
  to see if there is any indication of a raster. With the light bulb, not
  everything will be normal but some life would be a good sign. Even a
  pulsating light bulb may just mean that the light bulb is too small for the
  monitor power requirements. It may be safe to try a higher wattage bulb.
• However, if the bulb glows at close to full brightness, there is probably
  still some fault elsewhere. Don’t be tempted to remove the light bulb just
  yet. There is still something wrong. Continue to search for shorted parts.

  See if you can locate any other large power transistors in metal (TO3) cans
  or large plastic (TOP3) cases. There may be a separate power transistor
  that does the low voltage regulation or a separate regulator IC or hybrid.
  As noted, some monitors have a switchmode power supply that runs off
  a different transistor than the HOT. There is a chance that one of these
  may be bad.

  If it is a simple transistor, the same ohmmeter check should be performed.

If none of this proves fruitful, it may be time to try to locate a schematic
or a service center.

Internal fuse blew during lightning storm (or elephant hit power pole)

Power surges or nearby lightning strikes can destroy electronic equipment.
However, most of the time, damage is minimal or at least easily repaired.
With a direct hit, you may not recognize what is left of it!

Ideally, electronic equipment should be unplugged (both AC line and phone
line!) during electrical storms if possible. Modern TVs, VCRs, microwave
ovens, and even stereo equipment is particularly susceptible to lightning and
surge damage because some parts of the circuitry are always alive and therefore
have a connection to the AC line. Telephones, modems, and faxes are directly
connected to the phone lines. Better designs include filtering and surge
suppression components built in. With a near-miss, the only thing that may
happen is for the internal fuse to blow or for the microcontroller to go
bonkers and just require power cycling. There is no possible protection
against a direct strike. However, devices with power switches that totally
break the line connection are more robust since it takes much more voltage
to jump the gap in the switch than to fry electronic parts. Monitors and
TVs may also have their CRTs magnetized due to the electromagnetic fields
associated with a lightning strike – similar but on a smaller scale to
the EMP of a nuclear detonation.

Was the monitor operating or on standby at the time? If it was switched
off using an actual power switch (not a logic pushbutton), then either
a component in front of the switch has blown, the surge was enough to
jump the gap between the switch contacts, or it was just a
coincidence (yeh, right).

If it was operating or on standby or has no actual power switch, then
a number of parts could be fried.

Monitors usually have their own internal surge protection devices like MOVs
(Metal Oxide Varistors) after the fuse. So it is possible that all that is
wrong is that the line fuse has blown. Remove the case (unplug it first!) and
start at the line connector. If you find a blown fuse, remove it and measure
across the in-board side of fuse holder and the other (should be the neutral)
side of the line. The ohmmeter reading should be fairly high – more than 100
ohms in at least one direction. You may need to unplug the degaussing coil
to get a reasonable reading as its resistance may be less than 30 ohms. If
the reading is really low, there are other problems. If the resistance checks
out, replace the fuse and try powering the monitor. There will be three
possibilities:

1. It will work fine, problem solved.
2. It will immediately blow the fuse. This means there is at least one
   component shorted – possibilities include an MOV, line rectifiers, main
   filter cap, regulator transistor, horizontal output transistor, etc. You
   will need to check with your ohmmeter for shorted semiconductors. Remove
   any that are suspect and see of the fuse now survives (use the series
   light bulb to cut your losses – see the section:
   The series light bulb trick.
3. It will not work properly or appear dead. This could mean there are
   open fusable resistors other defective parts in the power supply or
   elsewhere. In this case further testing will be required and at some
   point you may need the schematic.

If the reading is very low or the fuse blows again, see the section:
Monitor blows fuse.

Fuse replaced (doesn’t blow) but monitor is still nearly dead

There may be a click indicating that the power relay is engaging (there could
be bad contacts though this isn’t that likely) and the degauss is probably
working now.

Since the fuse doesn’t blow now (you did replace it with one of the same
ratings, right?), you need to check for:

• Other blown fuses. Occasionally there are more than one in a monitor.
• Open fusable resistors. These are usually low values (a few ohms or less)
  and are in big rectangular ceramic power resistor cases or smaller blue or
  gray colored cylindrical power resistors. They are supposed to protect
  expensive parts like the HOT but often blow at the same time – or the
  expensive HOT or SMPS chopper sacrifices itself to save the 25 cent
  resistor.

If any of these test open, they will need to be replaced with flameproof
resistors of the same ratings. However, you can substitute an ordinary
resistor for testing purposes ONLY as long as you don’t leave the monitor
unattended.

If you find one bad part, still check other power components for shorts or
opens as more than one part may fail and just replacing that one may cause it
to fail again. These include (depending on your monitor): Rectifier diodes,
main filter capacitor(s), fuses and fusable resistors, horizontal output
transistor, regulator pass or chopper transistor.

Assuming nothing tests faulty so far, clip a voltmeter set on its 500 V or
higher scale across the horizontal output transistor and turn the power on.
Warning – never measure this point if the horizontal deflection is operating.
It is OK now since the monitor is dead. If the voltage here is 60 to 150 V,
then there is a problem in the drive to the horizontal output circuit. If it
is low or 0, then there are still problems in the power supply.

No picture but indications of power

The screen is blank with no raster at all. There are indications that the
power is alive – the status LEDs are lit and you can hear the normal
relay clicking sounds when you change video modes. This indicates that some
of the low voltages are present but these may be derived from the standby
supply.

Assuming there is no deflection and no HV, you either have a low
voltage power supply problem, bad startup circuit, or bad horizontal
output transistor (HOT)/bad parts in the horizontal deflection.

Check for bad fuses.

(If you have HV as indicated by static electricity on the front of the
screen and you hear the high pitched whine of the horizontal deflection
when it is turned on, then the following does not apply).

1. Use an ohmmeter to test the HOT for shorts. If it is bad, look for
   open fusable resistors or other fuses you did not catch.
2. Assuming it is good, measure the voltage on the collector-emitter
   of the HOT (this is safe if there is no deflection). You should see
   the B+ of between 60 and 150 V (typical) depending on mode (for a
   auto-scan monitor).
3. If there is no voltage, you have a low voltage power supply problem
   and/or you have not found all the bad/open parts. The flyback primary
   winding may be open as well.
4. If there is voltage and no deflection, you probably have a startup
   problem – all TVs and most monitors need some kind of circuit to kick start
   the horizontal deflection until the auxiliary power outputs of the flyback
   are available. Some designs use a simple multivibrator for this – a couple
   of transistors. Others power the horizontal oscillator IC from a special
   line-derived voltage.

   Look for pulses at the HOT base. If there are none, trace back to the
   driver and oscillator. Most likely: the power for startup is missing.

   Test the transistors if it is that type with an ohmmeter. If one is
   shorted, you have a problem. The usual way a TV service person would
   test for startup problems is to inject a signal to the base of the HOT
   of about 15.75 kHz. If the TV then starts and runs once this signal
   is removed, the diagnosis is confirmed. This is very risky for monitors
   and I would not recommend it – you can all too easily blow things up if
   not careful (including yourself).

If you hear the high pitched whine of the deflection (probably not for
workstation or SVGA computer monitors unless you are a bat) and/or feel
some static on the scree, confirm that the horizontal deflection and high
voltage are working by adjusting the SCREEN control (probably on the flyback).
If you can get a raster then your problem is probably in the video (or chroma)
circuits, not the deflection or high voltage.

Monitor deflection derived power supply faults

This section applies to studio video monitors, small computer terminals,
and most TVs, which derive many of their supply voltages from auxilary
windings on the flyback transformer.

The following are common areas of failure:

• Horizontal output transistor (usually a TO3 metal or TOP3 plastic case
  shorts out. This will usually blow a fuse or fusable resistor as well.
• Horizontal drive chain – horizontal oscillator, driver, or driver
  transformer. Newer monitors may use an IC for the oscillator and this can
  fail.
• Startup – There may be some kind of startup circuit which gets the whole
  thing going until the auxiliary voltages are available. This could be
  as simple as a multivibrator or transistor regulator to provide
  initial voltage to the horizontal oscillator chip or circuit.
• Output rectifier diodes can fail shorted and load down the outputs to
  the point of shutting down.
• Some load could be shorted or a capacitor could be shorted leading to
  overload and shutdown.
• Flyback transformer can have shorted windings which load down the output.
  These (primary shorts in particular) may cause the horizontal output
  transistor to fail as well. Common problem with older MacIntosh computers
  and video terminals. Some secondary faults may not be instantly destructive
  but result in little or no high voltage and overheating.
• Cold solder joints or other bad connections – monitors tend to have these
  as a result of temperature cycling and bad manufacturing. (Is this sounding
  repetitive yet?)
• Sometimes there is a series regulator after the filter cap and this could
  be bad as well.

Without a schematic, I would attempt to trace the circuit from the main
filter cap or output of the line operated switchmode power supply assuming
that has the proper (approx. 60-120 VDC depending on scan range) voltage.

If you can locate the horizontal output transistor, see if there is voltage
on its collector, should be the same. If there is, then there is probably
a drive problem. If you have an ECG or similar semi cross reference,
that will help you identify the ICs and transistors and locate the relevant
portions of the circuitry.

If there is no voltage at the horizontal output transistor, then there
is probably a blown fuse or bad connection somewhere or a fault in the
line operated SMPS if there is one. However, the fuse may have blown
due to a fault in the SMPS or horizontal deflection.

Power-on tick-tick-tick or click-click-click but no other action

A variety of problems can result in this or similar behavior. This applies
to both monitors using SMPSs and flyback derived power supplies.
Possibilities include:

• Lack of horizontal drive. The main regulator is cycling on overvoltage due
  to very little load.
• Excessive load or faulty power supply cycling on its overcurrent protection
  circuit. The sound in this case may be more like a tweet-tweet-tweet or
  flub-flub-flub, however – see the section: Dead monitor
  with audible whine, periodic tweet or flub, and low-low voltage.
• HV shutdown, or some other system detecting an out of regulation condition.
  However, in this case, there should be some indication that the deflection
  and HV is attempting to come up like momentary high pitched deflection whine,
  static on the screen, etc.
• A dried up main filter capacitor or other filter capacitor in the low
  voltage power supply that is producing an out-of-regulation condition
• A problem with the microcontroller, relay or its driver, or standby
  power supply.

If you have a Variac, vary the line voltage and observe the
monitor’s behavior. It may work fine at one extreme (usually low) or the
other. This might give clues as to what is wrong.

Dead monitor with audible whine, periodic tweet or flub, and low-low voltage

A monitor which appears to be dead except for an audible whine or a once a
second or so tweet or flub coming from the SMPS usually indicates an overload
fault in the power supply itself or a short in one of its load circuits
(usually the main B+). In most cases, the voltages (including B+) will be
reduced to a fraction of their normal value (and/or be pulsing along with the
animal sounds) as a result of the overload. The power (or other) LED may be
weak or flashing as well. Flyback derived power supplies are less likely to
exhibit these symptoms.

Note: using too small a series light bulb while testing for the size of the
monitor may also result in this condition. If you have found and replaced a
bad part, it increase the wattage of the light bulb and try again. If the
frequency of the cycling decreases – i.e., it stays up longer, it may be safe
to remove the light bulb entirely.

Summary of possible causes:

• Shorted rectifiers or capacitors on secondary side of SMPS.
• Other problems in the power supply or its controller like bad caps.
• Shorted HOT.
• Flyback with shorted turns or breakdown in focus/screen divider network.
• Short or excessive load on secondary supplies fed from flyback.
• Short in horizontal yoke windings.
• Bad solder connections.

Note that a whine may be perfectly normal for your monitor if there is no video
input – confirm that there is a signal that is compatible with the monitor’s
scan rate(s) and type of sync (e.g., separate, composite, or sync-on-green).

However, where a confirmed good video input is present, this may indicate an
overloaded low voltage switching power supply.

The whine is caused by the switching power supply’s chopper frequency
dropping down due to the overload. The periodic tweet or flub is caused by
the SMPS attempting to come up, sensing the excessive load, and restarting.

Test the B+ input to the flyback.

If it is near zero, test the HOT for shorts and replace if defective, but
continue testing with a series light bulb and/or Variac. There may be
something causing the HOT to go bad like a shorted flyback or bad damper diode
or snubber cap.

If the voltage is not zero but is low (e.g., it should be 120 V but is
only 60 V) or fluctuating in time with the tweet or flub, there may be a
problem with:

1. The SMPS. Test with a substitute load like a 40 W light bulb or power
   resistor. If the supply now outputs full voltage, it is probably fine.
   For a power resistor, select a value such that the load at the expected
   voltage will be about 1/2 to 2/3 of the nameplate power rating of the
   monitor.

   One common type of failure are shorted rectifiers in the switching supply
   or secondary supplies running off the flyback. The HFR854s (one
   popular type in monitors) or other high speed high efficiency rectifiers in
   the output side of the switching power supply or flyback seem to like to
   turn into short circuits. (I had a couple of DOA monitors where this was
   the problem. so much for quality control!)

   WARNING: Unplug the monitor and discharge the main filter caps before
   attempting the following tests!

   Use an ohmmeter to check the various diodes in the power supply. The
   higher power diodes appear commonly as black cylinders about 3/8″ long by
   1/4 diameter – kind of like 1N400Xs on steroids. The resistance of the
   diodes in at least one direction should be greater than 50 ohms in-circuit.
   If you find one that is much less (like 0 or 5 ohms), then it is probably
   bad. Unsolder and check again – it should test infinite (greater than 1M
   ohms) in one direction. If it now tests good, there may be something else
   that is shorted.

   Replacements are available for about $0.25 from places like MCM Electronics.

2. Flyback (LOPT) transformer – shorted windings. See the document:
   Testing of Flyback (LOPT) Transformers.
3. Deflection yoke – shorted turns in the horizontal or geometry correction
   windings. See the section: Deflection yoke testing.
4. Excess load on one of the flyback’s secondaries. Disconnect all secondary
   output pins from the flyback if possible and see if your B+ returns to
   normal.
5. Improper drive to HOT. Inspect with an oscilloscope. The drive should
   match the horizontal rate of the video input with a high time (at .7 to 1 V
   or so) typically 75 to 95% of the total line time.

Monitor power cycling on and off

The power light may be flashing or if you are runing with a series light bulb
it may be cycling on and off continuously. There may be a chirping or clicking
sound from inside the set. (Note: using too small a light bulb for the size of
the monitor may also result in this condition.)

If there is a low voltage regulator or separate switching supply, it could be
cycling on and off if the horizontal output, flyback, or one of its secondary
loads were defective.

These symptoms are slightly different than those discussed in the section:
Dead monitor with audible whine, periodic tweet or flub,
and low-low voltage in that a picture may actually appear for an instant.

Verify that the main filter capacitor is doing its job. Excessive ripple
on the rectified line voltage bus can cause various forms of shutdown
behavior. An easy test is to jumper across the capacitor with one of
at least equal voltage rating and similar capacitance (make connections
with power off!).

Use a Variac, if possible, to bring up the input voltage slowly and see if
the monitor works at any point without shutting down. If it does, this
could be an indication of X-ray protection circuit kicking in, though this
will usually latch and keep the set shut off if excessive HV were detected.

Something could be breaking down like a capacitor or the flyback as the
voltage builds up to normal values

Startup problems – nothing happens, click, or tick-tick-tick sound

TVs and and small fixed scan rate monitors (e.g., CCTV or TV monitors, video
display terminals) usually incorporate some kind of startup circuit to provide
drive to the horizontal output transistor (HOT) until the flyback power supply
is running. Yes, TVs and many monitors boot just like computers.

There are two typical kinds of symptoms: power on click but nothing else
happens or a tick-tick-tick sound indicating cycling of the low voltage
(line regulator) but lack of startup horizontal drive.

Check the voltage on the horizontal output transistor (HOT). If no voltage
is present, there may be a blown fuse or open fusable resistor – and
probably a shorted HOT.

However, if the voltage is normal (or high) – usually 60-150 V depending
on scan rate (for an auto-scan monitor), then there is likely a problem with
the startup circuit not providing initial base drive to the HOT.

The startup circuits may take several forms:

1. Discrete multivibrator or other simple transistor circuit to provide
   base drive to the HOT.
2. IC which is part of deflection chain powered off of a voltage divider
   or transformer.
3. Other type of circuit which operates off of the line which provides
   some kind of drive to the HOT.

The startup circuit may operate off of the standby power supply or
voltage derived from non-isolated input. Be careful – of course, use
an isolation transformer whenever working on TVs and especially for power
supply problems.

Note that one common way of verifying that this is a startup problem is
to inject a 15 kHz signal directly into the HOT base or driver circuit
(just for a second or two). If the TV then starts up and continues to run,
you know that it is a startup problem.

Caution: be careful if you do this. The HOT circuit may be line-connected
and it is possible to destroy the HOT and related components if this is not
done properly. I once managed to kill not only the HOT but the chopper
transistor as well while working in this area. An expensive lesson.

I have also seen startup circuits that were designed to fail. Turning
the TV on and off multiple times would exceed the power ratings of the
components in the startup circuit. Some Zenith models have this ‘feature’.

When this situation exists, it could be that the circuit is not providing
the proper drive or that due to some other circuit condition, the drive
is not always sufficient to get the secondary supplies going to the point
that the normal circuits take over.

I would still check for bad connections – prod the circuit board with an
insulated stick when the problem reoccurs.

Reduced width picture and/or hum bars in picture

The most likely cause is a dried up main filter capacitor. Once the
effective capacitance drops low enough, 120 Hz (or 100 Hz in countries with
50 Hz power) ripple will make its way into the regulated DC supply
(assuming full wave rectification).

Another likely cause of similar symptoms is a defective low voltage
regulator allowing excessive ripple. The regulator IC could be bad
or filter capacitor following the IC could be dried up.

Either of these faults may cause:

1. A pair of wiggles and/or hum bars in the picture which will float up
   the screen. For NTSC where the power line is 60 Hz but the frame rate
   is 59.94 Hz, it will take about 8 seconds for each bar to pass a given
   point on the screen. (On some sets, a half wave recitifier is used
   resulting in a single wiggle or hum bar).

   For high scan rate computer monitors, the this may result in horizontal
   hum bars, wiggles, or other distortions that will drift up or down
   the screen based on the difference frequency between the power line
   and video refresh rate being supplied by the PC or workstation. A
   confirmation can be obtained by varying the scan rate and seeing if
   the rate of drift changes predictably.

2. Possible regulation problems resulting in HV or total shutdown or power
   cycling on and off.

The best approach to testing the capacitors is to clip a good capacitor of
approximately the same uF rating and at least the same voltage rating across
the suspect capacitor (with the power off). A capacitor meter can also
be used but the capacitor may need to be removed from the circuit.

Once the capacitors have been confirmed to be good, voltage measurements
on the regulator should be able to narrow down the problem to a bad IC
or other component.

Wiggling or jiggling picture

Depending on the frequency of the instability relative to the scan rate in
use, the symptoms may be that the entire picture is vibrating, that ripples
are moving up or down the screen, or something else. There may also be
variatons in brightness – hum bars – in the picture.

• Very high frequency oscillations will result in multiple waves or scalloped
  edges on the sides of the raster possibly extending into the picture itself.
  These patterns may or may not remain stationary.
• Low or power line frequency oscillations will result in the entire raster
  moving back and forth, vibrating, or 1 or 2 wiggles along the sides of the
  raster that move up or down the screen. The actual behavior will depend on
  the relative frequencies of the oscilations and the vertical scan rate.

When the vertical scan rate is set close to the local power line frequency,
effects resulting from power line interference or bad filter capacitors will
produce 1 or 2 wiggles or bars, and these will remain almost stationary on the
screen. Those caused by internal power supply stability problems may or may
not do this.

First, eliminate the possibility of external magnetic interference, power
line noise, or a video card/computer problem. Try the monitor in another
location and on another computer if possible. Or, try another similar monitor
in its place.

Once these causes have been ruled out, the most likely ones are:

• Dried up electrolytic capacitors in the power supply.
• A resistor or other component has changed value in the B+ (or other)
  regulator.

  For example, one very common monitor – the Gateway CS1572FS – uses a 91K, 1W
  resistor (R331) to set its 180 V B+ output. Invariably with use and age,
  its resistance increases in value leading to a vibrating raster and eventual
  failure of other parts.

• Bad connections.

Monitor doesn’t power up immediately

The monitor may do nothing, cycle on and off for a while, power up and then
shutdown in an endless cycle – or at least for a while. Then it comes
on and operates normally until it is turned off.

A couple of possibilities:

1. The main filter capacitor or other filter capacitors in the low voltage
   power supply is dried up and this can cause all kinds of regulation
   problems. Other regulating components may be marginal. This may be
   allowing excessive voltage to reach the output of the power supply and then
   the X-ray protection circuitry shuts you down.

   Try powering the monitor on a Variac when cold. Bring up the voltage
   slowly and see if there is some point at which it would stay on. If there
   is, then a regulation problem is likely. If the picture has serious hum
   bars in it, check the main filter capacitor(s) first.

2. Bad connections may be preventing the power supply from operating normally
   until the mainboard or components heat up a bit.

   Inspect the solder side of the mainboard for cracked solder connections.
   Some gentle poking and prodding with a well insulated stick may reveal the
   location though a problem that goes away once the unit heats up can be
   tough to identify!. The use of ‘cold spray’ may help. Also, clean and
   reseat internal connectors.

Also see the section: Old monitor requires warmup
period.

Old monitor requires warmup period

So, what else is new? In the old days, a TV or monitor was expected to take
a few minutes (at least) to warm up. We are all spoiled today. Of course,
you usually maintained a full time technician or engineer to fiddle with the
convergence adjustments!

If it just takes a while for the picture to become as bright as you like,
this is probably just a result of an old tired CRT (see the section:
Monitor
Monitor life, energy conservation, and laziness
and Brightening an old CRT. If,
however, nothing happens for a few minutes, then some component needs to be
powered for a while before it starts cooperatings. This is probably a dried
up capacitor in the power supply since that is drifting with temperature and
needs to be located with cold spray or a heat gun.

Adjustment or picture interactions

This describes problems such as turning up the brightness causes a loss of
sync or adjusting height also affects width or produces a wavy raster.
Or, a bright picture or opening a bright window results in a significant
change in picture size or wiggly edges. Or, the monitor simply decides to
shut down!

These may be caused by poor regulation in one or more low voltage power
supplies or and interaction between the high voltage and low voltage
power supplies – possibly a dried up capacitor if it is relatively old,
bad connections, or another faulty component. Measure the B+ to the
horizontal deflection (to the flyback, not the horizontal output transistor).
If it is changing with the problem, then a regulation problem is confirmed.
If this voltage is solid, you will need to check the others to see which
one is actually changing.

Shorted Components

A failure of the horizontal output transistor or power supply switchmode
transistor will blow a fuse or fusable resistor.

Look for blown fuses and test for open fusable resistors in the power circuits.
If you find one, then test the HOT and/or switchmode transistor for shorts.

Other possibilities: rectifier diodes or main filter capacitor.

While you are at it, check for bad connections – prod the circuit board with an
insulated stick when the problem reoccurs – as these can cause parts to
fail.

Monitor turns off after warming up

If you can turn it back on with the s momentary key or power button:

When it shuts off, do you need to push the power button once or twice
to get it back on? Also, does anything else about the picture or sound
change as it warms up?

1. If once, then the controller is shutting the TV down either as a result of
   a (thermally induced) fault in the controller or it sensing some other
   problem. Monitoring the voltage on the relay coil (assuming these
   is one) could help determine what is happening. The controller thinks
   it is in charge.
2. If twice, then the power supply is shutting down as the controller still
   thinks it is on and you are resetting it. A couple of possibilities
   here would be low voltage or high voltage regulation error (excessive
   high voltage is sensed and causes shutdown to prevent dangerous X-ray
   emission). A partially dried up main filter capacitor could also cause a
   shutdown but there might be other symptoms like hum bars in the picture just
   before this happened. Clipping a good capacitor across the suspect (with
   power off!) would confirm or eliminate this possibility.

If it uses a hard on/off switch, then this may be like pulling the plug
and would reset any abnormal condition.

Monitor shuts down with bright picture or when brightness is turned up

This is probably a protection circuit kicking in especially if turning power
off or pulling the plug is required to restore operation.

The detection circuit could be in the power supply or horizontal deflection
output circuit. It may be defective or the current may be too high for some
other reason. A couple of tests can be performed to confirm that it is due
to beam current:

• Determine if behavior is similar when adjusting the user brightness control
  and the screen (G2) pot (on the flyback) or master brightness control. If
  the monitor quits at about the same brightness level, overcurrent protection
  is likely.
• Disconnect the filaments to the CRT (unsolder a pin on the CRT socket) and
  see if it still shuts down under the same conditions. If it is overcurrent
  protection, shut down should now *not* take place since there is no beam
  current.

Relays in the Power Circuitry of monitors

What exactly is the purpose of such a relay? Why doesn’t the power
switch on the monitor just apply power directly instead of through a relay?

On a TV, the usual reason for a relay instead of a knob switch is to permit
a remote control to turn power on and off. If your TV does not have a remote,
then it is simply the same chassis minus 24 cents worth of circuitry to do the
remote function. Isn’t marketing wonderful?

On a monitor without any remote control, there can be two likely reasons:

1. Reduce the needed capacity of the on/off switch. High resolution
   monitors do consume a fair amount of power. A soft touch button may
   be more elegant or cheaper.
2. Allow for automatic power saving ‘green’ operation.

When replacing a relay, only unknown is the coil voltage. It is probably
somewhere in the 6-12 volt range. You should be able to measure this on
the coil terminals in operation. It will be a DC coil.

However, the relay controls the 125 VAC (or 220) which you should treat
with respect – it is a lot more dangerous than the 25kV+ on the CRT!

Almost certainly, the relay will have 4 connections – 2 for power and 2
for the coil. If it is not marked then, it should be pretty easy to
locate the power connection. One end will go to stuff near the AC line
and the other end will go to the rectifier or maybe a fusable resistor
or something like that. These will likely be beefier than the coil
connections which will go between a transistor and GND or some low voltage,
or maybe directly into a big microcontroller chip.

Of course, the best thing would be to get the schematic but with monitors
this may not be easy.

Once you are sure of the AC connections – measure across them while it is
off and also while it is on. While off, you should get 110-125 VAC.
While on and working – 0. While on and not working either 110-125 VAC
if the relay is not pulling in or 0 if it is and the problem is elsewhere.
We can deal with the latter case if needed later on. Note the even if the
relay contacts are not working, the problem could still be in the control
circuitry not providing the correct coil voltage/current, though not likely.

It may be expensive and/or difficult to obtain an exact replacement, but
these are pretty vanilla flavored as relays go. Any good electronics
distributor should be able to supply a suitable electrical replacement
though you may need to be creative in mounting it.

What is a posistor?

A posistor is a combination of a PTC (Positive Temperature Coefficient)
resistor and another resistor-element to heat it up and keep it hot.
Sometimes, these will go by the name posistor or thermistor. The heater
is a disk shaped resistor across the power line and the themister
is a disk shaped device in series with the degauss coil. They are in
clamped together to be in close contact thermally. You can pry off the
lid and see for yourself.

The most common failure mode is for the part to short across the line.

Its function is to control degauss, so the only thing you lose when you
remove one of these is the degauss function on power-on. When you turn
the TV or monitor on, the PTC resistor is cold and low resistance. When
heated, it becomes very high resistance and turns off the degauss coil
but gradually – the current ramps down to zero rather than being abruptly
cut off..

Computer Component Source stocks a wide variety, I believe but it may be
cheaper to go direct to the manufacturer if they will sell you one.

Flameproof Resistors

Flameproof Resistor or Fusable Resistor are often designated by the
symbol ‘FR’. They are basically the same. The designation “Flameproof”
means that if they fail due to excessive current, there will be no
chance of, well, them going up in flames. 🙂 They will also have a
power rating and thus can act as a protective device, though a specific
circuit may not depend on a precise fuse rating, rather that the
resistor will open with massively excessive current.

You may see these in the switchmode power supplies used in TVs and monitors.
They will look like power resistors but will be colored blue or gray, or may
be rectangular ceramic blocks. They should only be replaced with flameproof
resistors with identical ratings. They serve a very important safety function.

These usually serve as fuses in addition to any other fuses that may be
present (and in addition to their function as a resistor, though this isn’t
always needed). Since your FR has blown, you probably have shorted
semiconductors that will need to be replaced as well. I would check
all the transistors and diodes in the power supply with an ohmmeter.
You may find that the main switch mode transistor has decided to turn into
a blob of solder – dead short. Check everything out even if you find one
bad part – many components can fail or cause other components to fail
if you don’t locate them all. Check resistors as well, even if they look ok.

Since they function as fuses, flameproof resistors should not be replaced
with higher wattage types unless specifically allowed by the manufacturer.
These would not blow at the same level of overload possibly resulting in
damage to other parts of the circuitry and increasing the risk of fire.

Then, with a load on the output of the power supply use a Variac to bring
up the voltage slowly and observe what happens. At 50 VAC or less, the
switcher should kick in and produce some output though correct regulation
may not occur until 80 VAC or more. The outputs voltages may even be
greater than spec’d with a small load before regulation is correct.

Deflection Problems

Deflection fundamentals

Note: the following is just a brief introduction. For more detailed deflection
system theory of operationo and sample circuits, see the document:
TV and Monitor Deflection Systems.

The electron beams in the CRT need to be scanned horizontally and vertically
in a very precise manner to produce a raster – and a picture.

For NTSC and PAL, the horizontal scan rates are 15,734 and 15,625 Hz
respectively, the vertical scan rates are 60 and 50 Hz (approximately)
respectively.

For PCs and workstation monitors, a wide range of scan rates are used.

For example:

      Standard      Horizontal, kHz  Vertical, Hz
    ------------------------------------------------
    MDA               18.43           50
    CGA               15.75           60
    EGA               15.75-21.85     60
    VGA               31.4            60-70
    SVGA (800x600)    35-40           50-75+
    SVGA (1024x768)   43-52+          43-75+  
    SVGA (1280x1024)  64-72+          60-75+
    Workstations      64-102+         60-76+

Even in high resolution fixed frequency monitors, these high horizontal
(in particular) scan rates necessitate some fancy circuit design. All
components are running under stressful conditions and it is amazing that
failures are not more common.

With auto-scan monitors, the complexity of the circuits increases dramatically
to accommodate the wide range of horizontal scan rates. Relays or electronic
switches are used to select power supply voltages, tuning components, and
to make other alternations in the deflection circuits to handle DOS VGA
one minute and Autocad 1280×1024 the next. It comes as no surprise that
the most stressful time for a monitor may be when switching scan rates.

Unfortunately, successfully diagnosing problems dealing with the scan
switching logic and circuitry is virtually impossible without a schematic.

The deflection yoke includes sets of coils for horizontal and vertical
scanning oriented at 90 degrees with respect to each other. Additional
coils are needed to correct for pincushion and other geometric defects.

The deflection circuits must be synchronized and phase locked to the
incoming video signal.

Therefore, we have the following functions:

1. Sync separator to obtain horizontal and vertical synchronization pulses
   for monitors with composite video or sync inputs. Input sync detectors
   and auto polarity switching circuits as needed for separate horizontal
   and vertical sync inputs.
2. Horizontal oscillator which locks to horizontal sync pulses.
3. Horizontal drive followed by horizontal output which feeds deflection
   yoke (and flyback for HV and other voltages), Yoke requires a sawtooth
   current waveform for linear horizontal deflection. Horizontal output
   in all but the smaller TVs or monitors is a large discrete power
   transistor, most often an NPN bipolar type.
4. Vertical oscillator which locks to vertical sync pulses. Yoke requires
   sawtooth waveform for linear vertical deflection.
5. Vertical drive/output which feeds vertical deflection yoke. Newer TVs
   and monitors use ICs for vertical drive and output.
6. Various additional deflection signals to correct for the imperfections
   in the geometry of large angle deflection CRTs. These may be fed into
   the normal deflection coils and/or there may be separate coils mounted
   on the neck of the CRT.
7. Auto-scan deflection control and selection circuitry (auto-scan monitors
   only), probably controlled by a microprocessor which stores scan
   parameters for each scan rate and automatically detects the appropriate
   settings to use by analyzing the input video. For horizontal deflection,
   the usual way of size constant regardless of scan rate is to scale the
   B+ to the HOT with horizontal frequency. Thus, VGA resolution may us
   60 V B+ while 1280×1024 at 75 Hz may require 150 V. Various other
   components may need to be selected based on scan rate. Relays are often
   used for this selection since they are easy to control and can handle the
   voltages and currents in the various deflection circuits reliably.

See Symptoms of Some Common Deflection Problems when
referring to the specific descriptions below.

Monitor display is off-center

These sorts of problems usually relate to the picture shifting when switching
between applications or between DOS and Windows. First, make sure you are
using the correct monitor settings and video drivers. Note that a fraction
of a mm offset may be normal and you are just too fussy!

If you have a setup program for your video card:

1. Make sure you are running well within the accepted scan rates for each
   resolution.
2. Toggle sync polarity and see if this makes any difference.
3. Adjust H position or phase and see what this does.

Also make sure your cables are secure. While a bad connection would likely
messed things up worse, it won’t hurt to check. Assuming none of this helps,
your monitor may have a problem though it is not likely to be major (in
a relative way). If you still like the monitor, repair may be worth the
money.

Gross problems in size or position at certain scan rates

First, make sure you are not specifying incorrect scan rate for your monitor.
Check your video card setup and/or monitor selection in Win95/98 as above.

Assuming you are not violating the scan rate specifications but have a
picture that is twice the height of the screen and one half the width,
for example, this could indicate a failure in the scan rate switching
circuitry of an auto-scan monitor. Either the logic is faulty and ordering
the wrong selections for power supply voltage and tuning components or the
relays or the relevant parts are faulty. This could be due to bad connections
as well – quite likely in fact. Also, try to reset the afflicted parameters
using the digital controls (if relevant) and confirm that your video card
is putting out the correct scan rate – try another monitor or examine the
video signals with an oscilloscope.

Try prodding the circuit boards with an insulated stick – this may identify
bad connections or unstick a sticky relay.

A schematics will likely be needed to proceed further with these sorts of
problems.

Reduced width

Complaints about the picture not filling the screen with computer monitors
are common but may not indicate problems (except with your expectations).
Older monitors, in particular, often did not allow a full screen display
at certain resolutions. There may be underscan modes/switches as well.
Keep in mind that advertizing a large diagonal CRT does not necessarily
imply that you can fill it!

However, if this problem just happened with no changes to your computer system
(video card, scan rates, O/S), then the following are possibilities:

• The B+ to the horizontal output is lower than normal. The way width
  control functions is that as you increase the horizontal scan rate, the B+
  to the HOT must increase to keep the width constant. It could be that yours
  is low to start with and not tracking scan rate changes either.
• A bad capacitor might also result in reduced width but I would expect
  non-linearity as well.
• As noted in the section: Gross problems in size or
  position at certain scan rates, there could be problems in the scan rate
  switching circuitry selecting incorrect components for certain scan rates.
• There might be a bad (low value or high ESR) decoupling capacitor.
  Scope the rail after the low-value decoupling R for H-rate stuff.
  There shouldn’t be anything significant. If there is, the ESR of the
  decoupling capacitor is too high or its value is too low. Seen it
  often where it also cooks the decoupling R, because the efficiency of
  the H-out becomes poor. (gwoods@albany.net (Gary Woods).)
• A more unlikely possibility is a open yoke winding. The horizontal
  deflection yoke consists of multiple windings in parallel so it is
  theoretically possible for one or more of these to open up. I don’t
  know what effects the associated detuning of the horizontal output
  circuit would have in this case.

Can incorrect or missing video damage my monitor?

The short answer is – quite possibly. Don’t push your luck.

Mostly, there are problems at scan rates which exceed the monitor’s
specifications (low or high). However, some poorly designed monitors or just
a particular combination of events can blow a monitor with too low a
scan rate or an absent or corrupted signal input. There was one case
where a very expensive high performance monitor would consistently blow
its horizontal deflection circuits when driven by a particular ATI
video card. It turned out that during the power-on self test of the ATI
BIOS, just the wrong video timing was being generated for a fraction of
a second – but that was enough.

As far as scan rate limits, there is no way of knowing – it really all
depends on the quality of the design of your monitor. Some will happily
run continuously at 25% above specifications. Other will blow out totally
at the first excuse.

The specification that is likely to be more critical is the horizontal rate
as it probably puts more stress on the components than the vertical rate.
I have found that as you approach the upper limits, there is a good chance
that the geometric accuracy of the raster near the top of the screen may
start to deteriorate due to lock in problems as well. However, it would be
foolhardy to depend on this sort of behavior as an indication of going over
the edge.

It will be much too late when you find out. If the manual says 75 Hz V and
64 kHz H, stay below **both** of these. If you exceed the safe ratings and
the design isn’t really good, there is the possibility of blowing components
in the horizontal deflection and high voltage sections which will result in
expensive repair bills. You will likely get no warning of impending failure.
In addition, even if the monitor does not immediately turn into a pile
of smoking silicon and plastic, components may be under more stress and
running at higher levels of power dissipation. Total failure may be just
around the corner. More subtle degradation in performance may occur over
time as well.

You won’t see the difference anyhow beyond 75 Hz and your programs may
run slightly faster at lower refresh rates since the video is not using
as much bandwidth (however, the difference here may be very slight or
non-existent depending on your board, computer, applications, etc.).

Picture squeezed in then died

You were happily playing ‘Doom’ when the sides of the picture squeezed in two
inches or so when the entire monitor went dead – has remained like this since.
There is no activity at all from the tube. Has it died? How much time,
effort, and expense to fix?

No, it’s not dead, at least it certainly is not the picture tube.

You probably shot the monitor instead of the bad guys!

Is there any indication of light on the screen? Any indication of the
horizontal deflection running at all as evidenced by static on the screen?

In any case, there is a problem in the horizontal deflection and you probably
have no high voltage as well assuming no light on the screen.

The fact that it squeezed in first indicates that a partial short or other
fault may have developed in the horizontal deflection circuits – possibly
the deflection yoke or flyback transformer. It could also have been a bad
connection letting loose. Once it failed completely, the horizontal output
transistor may have bought the farm or blown a fuse.

Horizontal deflection shutting down

Confirm that the horizontal deflection is shutting down along with the
high voltage if it is derived from horizontal deflection: listen
for the high pitched deflection whine (NTSC/PAL/CGA), test for static on
the screen, see if the CRT filaments are lit, turn up the brightness and/or
screen control to see if you can get a raster. Some possibilities:

• Power is failing to the horizontal output transistor – this could be
  due to a low voltage power supply problem, bad connection, etc.
• Base drive to the horizontal output transistor is failing – could be a
  fault in the horizontal oscillator or bad connection.
• Problem with the flyback transformer or its secondary loads (flyback
  may provide other power voltages).
• X-ray protection is activating – either due to excess HV or due to a
  fault in the X-ray protection circuitry.

If the problem comes and goes erratically it sounds like a bad connection,
especially if whacking has an effect. If it comes and goes periodically,
then a component could be heating up and failing, then cooling, etc.

Horizontal squashed

A very narrow picture may indicate problems with the power supply to the
horizontal deflection circuits, incorrect scan rate selection or defective
components, faulty deflection yoke, or bad connections.

If the size is erratic and/or gently whacking the monitor makes the width
change, bad connections are likely. See the section:
Monitor manufacturing quality and cold solder joints.

Confirm that your video card is running at the proper scan rate – particularly
that it is not violating the monitor’s specifications. An excessive horizontal
scan rate is a common cause of a reduced width raster. Try its software
setup adjustments as these may have been lost.

Beyond this, a schematic will probably be needed to isolate the fault.

Monitor non-linearity

Most modern monitors are nearly perfect with respect to linearity.
There are almost never any user adjustments and there may not even be any
internal adjustments. See the section: Position, size,
and linearity adjustment.

A sudden change in linearity or a monitor that requires a warmup period
before linearity becomes acceptable may have a bad component – probably
a capacitor in the horizontal deflection circuits. For the latter, try
some cold spray or a heatgun to see if you can locate the bad part.

(From: helio (mmccann@usa.pipeline.com).)

You should likely begin in the area immediately around the HOT, perhaps
there might be a high frequency NP (non polarized) electrolytic just
starting to go. Some larger monochrome monitors actually have working H-lin
adjustment coils (believe it or not) especially if they are older ones. But
most are glued/potted down or fixed value. If you locate it (the coil) the
problem should be nearby.

Picture squeezed on both left and right side of screen

“I’m trying to repair a Target DN-1564 monitor with a problem in the
horizontal deflection: on both the left and right side of the screen
the picture gets squeezed together, regardless of H-width and other
settings. I’ve checked most semiconductors in this part, but I can’t
find anything wrong there.”

This sounds like an S-correction capacitor may have too small a value or
failed open. Check the capacitors in the vicinity of the deflection yoke
connector and HOT. It could be due to bad connections as well.

S-correction is needed to linearize the horizontal scan (and vertical as well
scan but that is a separate circuit). Without S-correction, the scan current
would be nearly linear. This would result in greater coverage in a given
time near the edges of high deflection angle CRTs. The picture would appear
stretched near the edges In this case, the correction appears excessive.

(From: David Henniker (david.henniker@cableinet.co.uk).)

I had a similar problem with a monitor (here in Edinburgh Scotland).
The S-correction cap was open-circuit altogether. Other caps in parallel
allowed the distorted scan. If it had been a TV there wouldn’t have been
other caps in parallel and the result would have been no line scan, maybe
a vertical line (line collapse) or nothing at all.

Vertical squashed

This means the vertical size is reduced with or without distortion.

Before attacking the circuitry, make sure your vertical scan rate is within
the monitor’s capabilities and that the user vertical size control is adjusted
properly. If there is no distortion, this is likely as many (but not all)
circuit problems would result in non-linearity or cutoff of the top or bottom
portions of the picture. All you may need to do is change your computer’s
video settings! Swap the monitor or computer to be sure it is not a problem
with the video card.

However, if failure happened suddenly and the vertical is squashed at all scan
rates, this is likely a vertical deflection problem – possibly a bad capacitor,
bad connection, bad flyback/pumpup diode, or other component. None of these
should be very expensive (in a relative sort of way).

If the symptoms change – particularly if they become less severe – as the unit
warms up, a dried up electrolytic capacitor is most likely. If they get
worse, it could be a bad semiconductor. Freeze spray or a heat gun may be
useful in identifying the defective component.

It is often easiest to substitute a good capacitor for each electrolytic in
the vertical output circuit. Look for bad connections (particularly to the
deflection yoke), then consider replacing the vertical output IC or
transistor(s).

A defective deflection yoke is also possible or in rare cases, a bad yoke
damping resistor (e.g., 500 ohms, may be mounted on the yoke assembly itself).

Where the entire top half or botton half of the picture is squashed into
into the center (i.g., only half the picture shows), a missing power supply
voltage, defective vertical output IC, or a component associated with it
is likely bad. A bad connection or blown fusable resistor may be the
cause of a missing power supply voltage.

The following are NOT possible: CRT or flyback (except possibly where it
is the source for a missing power supply voltage but this is more likely
just a bad solder connection at a flyback pin ). I am just trying to
think of really expensive parts that cannot possibly be at fault. 🙂

Keystone shaped picture

This means that the size of the picture is not constant from top to bottom
(width changes) or left to right (height changes). Note that some slight
amount of this is probably just within the manufacturing tolerance of the
deflection yoke and factory setup (geometry magnet placement, if any). With
a monitor, such defects are more noticeable than with a TV since much of the
display is of rectangular boxes – i.e., windows, lines of text, graphics, etc.
Furthermore, the monitor is usually run just barely underscanned to maximize
the viewing area without cutting anything off. Any deviations from perfection
show up in relation to the CRT bezel.

However, a sudden increase may indicate a problem with the deflection yoke.

An open or short in a winding (or any associated components mounted on the yoke
assembly) will result in the beam being deflected less strongly on the side
where that winding is located. However, with a high scan rate monitor, there
may be many individual windings connected in parallel in the yoke so the effect
of only one opening up may not be as dramatic as with a TV where there may only
be a single pair of windings for the horizontal and another for the vertical.

A simple test of the yoke in this case can be performed by simply swapping
the connections to the yoke for the affected direction (i.e., if the width
changes from top to bottom, interchange the connections to the vertical
windings).

• If the keystone shape remains the same (but of course the picture flips),
  it is likely the yoke. The bad yoke winding is the one for the other
  axis (than what you swapped – if you just swapped the vertical, it is the
  horizontal yoke that has a short or open).
• If the keystone shape flips, it is a circuit problem (see below).

See the section: Deflection yoke testing.

If the monitor has been dropped off a 20 story building, the yoke may have
shifted its position on the neck, of the CRT resulting in all sorts of
geometry and convergence problems (at the very least).

(From: James Poore (aw133@lafn.org).)

I have seen the ‘reverse keystoning’ in several monitors and the fix is
usually the same. In the horizontal leg of the pincushion transformer are 1
or more electrolytics to ground. The caps have + going to transformer and –
to ground. Anyway when they start loosing capacitance and/or become leaky the
reverse keystoning effects become more pronounced.

Picture size changing

If the picture area is expanding or contracting without any changes to your
video card settings or other software. then there is a problem with the power
supplies in the monitor. This would be confirmed if the change is (1) gradual
over the course of say, an hour, and/or (2) gently whacking the monitor has
some effect indicating bad internal connections. Software problems would not
result in either of these characteristics.

Note that if the change is very small – say, less than 1 or 2%, then it may
simply be normal for your monitor due to poor design or the use of inferior
components – some parts associated with power supply regulation may be
changing value as the monitors warms up.

A way to confirm that something is drifting due to thermal problems would
be the monitor from another computer and see if the same thing happens.
Just powering the monitor by itself (but not in any power saving mode) might
also work for this test.

One possible cause could be that the high voltage is drifting gradually
due to a faulty component – increasing and making the beam ‘stiffer’ or
vice-versa. If this is the case there might also be a gradual change in
brightness as well (decreasing image size -> increase in brightness).
Alternatively, the HV may be stable but the power to both H and V deflection
is gradually changing.

Excess high voltage can increase the X-ray emissions and any kind of power
supply problems may ultimately result in total failure and an expensive
repair. Therefore, these symptoms should not be ignored. See the sections
on low voltage and high voltage power supply problems.

Monitor will not sync

For SVGA monitors, check that the sync pins in the video connector are not
broken or bent. On the VGA HD15 connector, these are pin 13 (H) and 14 (V).

For monitors using BNC cables, first make sure that the cable connections
are correct – interchange of H and V sync or G with one of the other video
signals (sync-on-gree setups) can result in all kinds of weird sync problems.

There are a wide variety of causes for a monitor that will not display
a stable or properly configured image. Among the symptoms are:

• Lack of sync horizontal – drifts smoothly horizontally. Depending on the
  difference between the video horizontal rate and the free-run frequency of
  the horizontal oscillator, the picture may be torn left or right (as shown
  in Symptoms of Some Common Deflection Problems
  or have multiple images superimposed horizontally. The situation where the
  picture is neatly split horizontally (which is what you might expect) is a
  special case where the frequencies are virtually the same. The key symptom
  common to all these is that there IS vertical lock (no blanking bar visible)
  AND there is no evidence that the deflection is even attempting to lock
  horizontally.

  This may mean that the horizontal sync signal is missing due to a bent,
  pushed in, or broken connector pin (pin 13) or other bad connection or a
  fault in the sync processing circuitry.

• Incorrect lock horizontal – torn picture (like a TV with the horizontal
  hold control misadjusted – if you remember these). This means that the
  sync signal is reaching the monitor but that it is having problem locking
  to it. Check the rate specifications – you may be exceeding them.
• Lack of sync vertical – rolls smoothly vertically. This may mean
  that the vertical sync signal is missing due to a bent, pushed in,
  or broken connector pin (pin 14) or other bad connection or a fault
  in the sync processing circuitry.
• Lock not stable vertical – jumps or vibrates vertically. This may be
  due to scan rate problems or a fault in the vertical sync circuitry of
  the monitor.
• Multiple or repeated images horizontally or vertically. There may be
  multiple images side-by-side, on top of each other, or interleaved.
  Most likely cause is driving the monitor with an incorrect scan rate.
  However, faulty circuitry could also be to blame.

Additional comments on some of these problems follow in the next few
sections.

Horizontal lock lost

A monitor which loses horizontal lock when changing resolutions, momentarily
losing the signal, or switching inputs may have a horizontal oscillator
that is way out of adjustment or has drifted in frequency due to aging
components. Alternatively, you may be running at scan rates that are not
supported by your monitor. Check its user manual (yeh, right, like you
have it!). Use the setup program that came with your video card to adjust
the default scan rates to match the monitor. Not only will it lock better,
you are less likely to damage the monitor by feeding it improper scan rates.

Note that the characteristics of this are distinctly different than
for total loss of sync. In the latter case, the picture will drift sideways
and/or up and down while with an off frequency oscillator, the torn up
picture will try at least to remain stationary.

Assuming you are have your video card set up properly – double check anyhow –
this could be a capacitor or other similar part. Or, the oscillator
frequency may just need to be tweaked (particularly with older monitors).
There may be an internal horizontal frequency adjustment – either a pot
or a coil – which may need a slight tweak. If a coil, use a plastic
alignment tool, not metal to avoid cracking the fragile core. There may
be several adjustments for auto-scan monitors – one for each major scan
range.

A schematic will be useful to locate the adjustment if any or to identify
possible defective parts. If it is a heat related problem try cold spray
or a heat gun in an effort localize the offending part.

Insufficient width (without hum bars)

If there are hum bars or wiggles in the picture, see the section:
Reduced width picture and/or hum bars in picture.

If both width and height are affected, the cause is likely something common:
low, low voltage power supply voltages or excessive high voltage (resulting
in a ‘stiffer’ beam).

(From: Jerry G. (jerryg@total.net).)

Lack of width is usually caused by defective power supply, low horizontal
drive to the yoke and flyback, defective circuits in the pincushioning
amplifier section, excessive high-voltage caused by defective voltage
regulation, and or excessive loading on the secondary side of the flyback.

Loss of horizontal sync (also applies to vertical) after warmup

The problem lies either in the horizontal oscillator or in the sync system.
If it really is a problem with sync pulses not reaching the oscillator,
the picture will move around horizontally and can be brought to hold
momentarily with the hold control. If the picture breaks up into strips,
there is a problem in the horizontal oscillator. If there is an accessible
hold control try rotating it: if the frequency is too far off, the picture
will not settle into place at any adjustment of the hold control. Look
around the horizontal oscillator circuit: all of the oscillator parts will
be right there, or check on the horizontal oscillator module. If only
one resolution on a auto-scan monitor is affected, the there could be a
separate oscillator circuit for each range.

(From: Randy Fromme.)

An additional cause of loss of h. sync can be bad filter cap(s) in the 6.3
VDC SMPS output. This 6.3 is dropped and pegged at +5 vdc by a zener diode
and powers the 7486 that is a common sync input circuit (allows either
polarity sync). Interestingly, it doesn’t affect the vertical sync (even
though the same 7486 is used for both H & V) because the SMPS itself is
synchronised to the horizontal frequency and thus the ripple is at
horizontal frequency as well. It’s an interesting failure from that
standpoint.

Replicated or offset multiple images

Multiple images on the screen horizontally or vertically indicate that
the scan rate is way off (by a factor equal to the number of complete
pictures.) This could be a fault in the monitor or you could be running
way outside of the monitor’s specifications. Even slightly exceeding
these for the horizontal or vertical may confuse the scan rate selection
logic and result in the monitor setting itself with incorrect scan rate
settings.

A situation where successive sweeps alternate position slightly resulting
in double or triple images may be caused by a incorrect or out of range
video timing, a bad component, or improper sync signals.

Check the settings of the video card and any sync termination or selection
on the monitor. Beyond this, a schematic will be required.

Part of picture cut off

The following applies if the part of the picture is missing but not
otherwise squashed or distorted. For example, 85% is missing but the
portion still visible is normal size.

Wow! That’s an interesting one, more so than the typical run-of-the-mill
“my TV just up and died on me”. Or, “my pet orangutan just put a hole
in the CRT, what should I do”?

With a monitor, this is more likely than a TV. But the cause is probably
not in the monitor (though not impossible). Check that your video parameters
are set up correctly (particularly if you have full control of them as with
Linux). You may have set the active too short or blanking too long.

If your video is confirmed to be OK (looking at it with an oscilloscope would
be best), then with the size of the picture fragment correct but 85% missing,
check waveforms going into the vertical output stage. The supply voltage is
probably correct since that often determines the size. It almost sounds like
the waveform rather than being mostly on (active video) and off for the short
blanking period is somehow only on during the last part of the active video
thus giving you just the bottom of the picture. If there is a vertical output
IC, it may be defective or the blanking input to it may be corrupted. The
problem may be as far back as the sync separator. Then again who knows,
schematics would be really handy.

Bright or dark bars on edge of picture (horizontal or vertical)

These may be sharp-edged or blurry. The latter could result when a portion
of the active video is unblanked during retrace.

An oscilloscope would help greatly in identifying the source of the problem.

Single Vertical Line

CAUTION: To prevent damage to the CRT phosphors, immediately turn down the
brightness so the line is just barely visible. If the user controls do not
have enough range, you will have to locate and adjust the master brightness or
screen/G2 pots.

Since you have high voltage, the horizontal deflection circuits are almost
certainly working (unless there is a separate high voltage power supply –
almost unheard of in modern TVs but possible in some higher performance
monitors).

Check for bad solder connections between the main board and the deflection
yoke. Could also be a bad horizontal coil in the yoke, linearity coil, etc.
There is not that much to go bad based on these symptoms assuming the high
voltage and the horizontal deflection use the same flyback. It is almost
certainly not an IC or transistor that is bad.

Single Horizontal Line

CAUTION: To prevent damage to the CRT phosphors, immediately turn down the
brightness so the line is just barely visible. If the user controls do not
have enough range, you will have to locate and adjust the master brightness or
screen/G2 pots.

A single horizontal line means that you have lost vertical deflection.
High voltage is most likely fine since there is something on the screen.

This could be due to:

1. Dirty service switch contacts. There is often a small switch on the
   located inside on the main board or perhaps accessible from the back. This
   is used during setup to set the color background levels. When flipped
   to the ‘service’ position, it kills vertical deflection and video to the
   CRT. If the switch somehow changed position or got dirty or corroded
   contacts, you will have this symptom. Flip the switch back and forth
   a couple of times. If there is some change, then replace, clean, resolder,
   or even bypass it as appropriate.
2. Bad connection to deflection yoke or other parts in vertical output
   circuit. Bad connections are common in TVs and monitors. Check
   around the pins of large components like transformers, power transistors
   and resistors, or connectors for hairline cracks in the solder. Reseat
   internal connectors. Check particularly around the connector to the
   deflection yoke on the CRT.
3. Bad vertical deflection IC or transistor. You will probably need
   the service manual for this and the following. However, if the
   vertical deflection is done with an IC, the ECG Semiconductor
   Master Substitution guide may have its pinout which may be enough to
   test it with a scope.
4. Other bad parts in vertical deflection circuit though there are not
   that many parts that would kill the deflection entirely.
5. Loss of power to vertical deflection circuits. Check for blown
   fusable resistors/fuses and bad connections.
6. Loss of vertical oscillator or vertical drive signals.

The most likely possibilities are in the deflection output stage or
bad connections to the yoke. To locate the vertical output circuitry without
a service manual, trace back from the deflection yoke connector. The vertical
coils will be the ones with the higher resistance if they are not marked.

Intermittent jumping or jittering of picture or other random behavior

This has all the classic symptoms of a loose connection internal to the
TV or monitor – probably where the deflection yoke plugs into the main PCB or
at the base of the flyback transformer. TVs and monitors are notorious for
both poor quality soldering and bad connections near high wattage components
which just develop over time from temperature cycling. The problem may happen
any time or more when cold or hot.

The following is not very scientific, but it works: Have you tried whacking
the monitor when this happened and did it have any effect? If yes, this would
be further confirmation of loose connections.

What you need to do is examine the solder connections on the PCBs in the
monitor, particularly in the area of the deflection circuits and power supply.
Look for hairline cracks between the solder and the component pins – mostly
the fat pins of transformers, connectors, and high wattage resistors. Any
that are found will need to be reflowed with a medium wattage (like 40W) or
temperature controlled soldering iron.

It could also be a component momentarily breaking down in the power supply
or deflection circuits.

Another possibility is that there is arcing or corona as a result of humid
weather. This could trigger the power supply to shut down perhaps
with a squeak, but there would probably be additional symptoms including
possibly partial loss of brightness or focus before it shut down. You may
also hear a sizzling sound accompanied by noise or snow in the picture,
static in the sounds, and/or a smell of ozone.

If your AC power fluctuates, an inexpensive monitor may not be well enough
regulated and may pass the fluctuations on as jitter. The video card is
unlikely to be the cause of this jitter unless it correlates with computer
(software) activity.

Horizontal output transistors keep blowing (or excessively hot)

Unfortunately, these sorts of problems are often difficult to definitively
diagnose and repair and will often involve expensive component swapping.

You have just replaced an obviously blown (shorted) horizontal output
transistor (HOT) and an hour (or a minute) later the same symptoms
appear. Or, you notice that the new HOT is hotter than expected:

Would the next logical step be a new flyback (LOPT)? Not necessarily.

If the monitor performed normally until it died, there are other possible
causes. However, it could be the flyback failing under load or when it
warms up. I would expect some warning though – like the picture shrinks
for a few seconds before the poof.

Other possible causes:

1. Improper drive to horizontal output transistor (HOT). A weak drive might
   cause the HOT to turn on or (more likely) shut off too slowly (greatly
   increasing heat dissipation. Check driver and HOT base circuit components.
   Dried up capacitors, open resistors or chokes, bad connections, or a driver
   transformer with shorted windings or a loose or broken core can all affect
   drive waveforms.
2. Excessive voltage on HOT collector – check LV regulator (and line
   voltage if this is a field repair), if any.
3. Defective safety capacitors or damper diode around HOT. (Though
   this usually results in instant destruction with little heating).
4. New transistor not mounted properly to heat sink – probably needs mica
   washer and heat sink compound.
5. Replacement transistor not correct or inferior cross reference.
   Sometimes, the horizontal deflection is designed based on the quirks
   of a particular transistor. Substitutes may not work reliably.
6. CRT shorting internally. If this happens only once in two weeks, it may
   be diffuclt to track down :-(.

The HOT should not run hot if properly mounted to the heat sink (using
heatsink compound). It should not be too hot to touch (CAREFUL – don’t
touch with power on – it is at over a hundred volts with nasty multihundred
volt spikes and line connected – discharge power supply filter caps first
after unplugging). If it is scorching hot after a few minutes, then you
need to check the other possibilities.

However, it is possible that the deflection circuit is just poorly designed
in the first place and it has always run hot (though it is unlikely to have
always been scorching hot). There is no way to know for sure without a
complete analysis of the circuit – not something that is a realistic
possibility. In this case, the addition of a small fan may make a big
difference in HOT survival. If you have it mounted on the case blowing on
the HOT, add a filter to minimize dust infiltration.

It is also possible that a defective flyback – perhaps one shorted turn – would
not cause an immediate failure and only affect the picture slightly. This
would be unusual, however. See the section: Testing
of flyback (LOPT) transformers.

Note that running the monitor with a series light bulb may allow the HOT
to survive long enough for you to gather some of the information needed
to identify the bad component.

Horizontal output transistors blowing at random intervals

The HOT may last a few minutes, days, months or years but then blow again.

These are among the hardest problems to locate. It could even be some peculiar
combination of user cockpit error – customer abuse – that you will never
identify. Yes, this should not happen with a properly designed monitor.

However, a combination of mode switching, loss of sync during bootup, running
on the edge of acceptable scan rates, and frequent power cycles, could test
the monitor in ways never dreamed of by the designers. It may take only one
scan line that is too long to blow the HOT. Newer horizontal processor chips
are quite smart about preventing HOT killing signals from reaching the
horizontal driver but they may not be perfect.

On the other hand, the cause may be along the lines of those listed in the
section: Horizontal output transistors keep blowing (or
excessively hot) and just not as obvious – blowing in a few days or weeks
instead of a few seconds but in this case, the HOT will likely be running very
hot even after only a few minutes.

Another possible cause for random failures of the HOT are bad solder
connections in the vicinity of the flyback and HOT (very common due to the
large hot high power components) as well as the horizontal driver and even
possibly the sync and horizontal oscillator circuits, power supply, or
elsewhere.

Steve’s comments on HOT replacement

(From: Steve Bell (service@bell-electronics.freeserve.co.uk).)

A HOT can fail on its own, but to save possibly having to change it again, I
always check the following:

If there is an electrolytic capacitor in the base circuit, check it with an
ESR meter. If you don’t have one, change it, they are cheap. Check the
tuning capacitor on the HOT collector for low value or open circuit. These are
low value and fairly critical, a capacitance meter is ideal. If you don’t
have one, a crude way to check is to use an analogue meter on x100 ohms and
watch the needle kick as the cap charges and compare to another cap same
value. Follow the HOT collector to the FBT, then from the FBT to a B+
regulator circuit if used. These often use a T0220 style FET or power
transistor, check for shorts. Locate the B+ filter cap on the feed from the
regulate to the FBT. Look for bulges and check with ESR meter. These caps are
typically 22 – 100 uF, 160 or 200V. Also visibly check the FBT for bulges or
splits. The only way to be sure the FBT is OK is to check with a FBT
tester/ringer or similar test equipment. Generally FBT’s in monitors are quite
reliable. This might sound like a lot to do, but when familiar with the
circuitry it doesn’t take long.

You could of course just change the HOT and all will be OK.

Vertical foldover

The picture is squashed vertically and a part of it may be flipped over and
distorted.

This usually indicates a fault in the vertical output circuit. If it uses
an IC for this, then the chip could be bad. It could also be a bad capacitor
or other component in this circuit. It is probably caused by a fault in
the flyback portion of the vertical deflection circuit – a charge pump that
generates a high voltage spike to return the beam to the top of the screen.

Test components in the vertical output stage or substitute for good ones.

Jagged or uneven vertical sweep

(From: Matthias Meerwein (Matthias.Meerwein@rt.bosch.de).)

I recently fixed two CRT display devices that both developed a very similar
problem: The vertical deflection was severely “jagged” with uneven line
spacing and partial vertical foldover. One patient was a nameless el-cheapo
28-inch TV (1988 made), the other one a 14 inch ADI SVGA monitor (1991
vintage).

My first suspicions were bad contacts on the PCB or yoke connectors or
isolation / connectivity problems inside the yoke. However, as the picture
didn’t change with warmup or tapping, those causes could be ruled out.
Examining the vertical deflection waveform with the scope showed the problem
being a parasitic high frequency oscillation around the vertical output ic.
On the TV, the oscillation extended over the entire scan period, while the
monitor exhibited the problem only near the vertical current zero cross.

In both cases I found the capacitor of the RC damping network on the amp
output to be at fault. Replacing it fixed the problem in both sets. This is
not the well-known dried-up-electrolytic problem described in the FAQ. The
culprits were mylar caps (.1 and .47 uF) looking completely unsuspicious.
They were probably a bit underrated voltage-wise (40 volts) so I replaced them
with 100 volts rated ones. The 2.2 ohms resistor in series with the cap was
fine in both cases.

Excessive width/pincushioning problems

This would mean that the left and right sides of the picture are ‘bowed’ and
the screen looks something like the diagram below (or the opposite – barrel
distortion).

However, the obvious symptoms may just be excess width as the curved sides may
be cut off by the CRT bezel.

 ============================================
 \                                          /
  \                                        /
   \                                      /
    \                                    /
     \                                  /
      \                               /
       |                              |
       |                              |
       |                              |
      /                                \
     /                                  \
    /                                    \
   /                                      \
  /                                        \
 /                                          \
==============================================

This geometry is the natural state of affairs with linear scan waveforms if
there were no correction. Normally, a signal from the vertical deflection
that looks something like a rectified sinewave is used to modify width based
on vertical position. There is usually a control to adjust the magnitude of
this signal and also often, its phase. It would seem that this circuit has
ceased to function.

If you have the schematics, check them for ‘pincushion’ adjustments and
check signals and voltages. If not, try to find the ‘pincushion’ magnitude
and phase adjustments and look for bad parts or bad connections in in the
general area. Even if there are no adjustment pots, there may still be
pincushion correction circuitry.

If the pincushion controls have absolutely no effect, then the circuit
is faulty. With modern digital setup adjustments, then it is even tougher
to diagnose since these control a D/A somewhere linked via a microprocessor.

Pincushion adjustment adds a signal to the horizontal deflection
to compensate for the geometry of the CRT/deflection yoke. If you have
knobs, then tracing the circuitry may be possible. With luck, you have
a bad part that can be identified with an ohmmeter – shorted or open.
For example, if the pincushion correction driver transistor is shorted,
it will have no effect and the picture will be too wide and distorted as
shown above.

However, without a schematic even this will be difficult. If the adjustments
are digital this is especially difficult to diagnose since you don’t even
have any idea of where the circuitry would be located.

Faulty capacitors in the horizontal deflection power supplies often cause
a similar set of symptoms.

Uncorrectable pincushion distortion with new monitor

“I just bought a new Sony 200SX 17″ monitor and I just can’t get the
pin-cushion control to work right. If I get the outer edges straight
then any window an inch or so from the edge will curve like crazy. The
only way around this is to shrink my screen size so I’ll have 3/4 in or
so of black space. This is very irritating since I am not getting the
15.9″ viewable size as advertised. Is this normal?”

(From: Jeroen H. Stessen (Jeroen.Stessen@philips.com).)

The distortion that you describe is called ‘inside pincushion’. Normally it
can be corrected by a dynamic S-correction circuit. Maybe Sony didn’t do a
too good job on this, or none at all. It may also be that the correction is
optimized for certain horizontal scan frequencies only, as dynamic S-correction
is a resonant circuit. You might want to test at another frequency.

(From: markmtf@earthlink.net).)

You may have a monitor that is at the edge of the acceptance tolerance, (which
is a defined acceptable variation for cost and production yield reasons). A
typical worse case tolerance may be up to 3mm of a deviation from a straight
line for the edges. This applies for all monitors and all manufacturers. Of
course some companies actually control the variation better than others, (and
some just say they do).

For reference; try using the “Recall” function which will set the adjustments
to the original factory settings. (This assumes that your video timing matches
the preset timing used in the factory). Check the infamous user manual.

Deflection yoke testing

A faulty deflection yoke can affect the geometry (size and shape) of the
raster, result in insufficient high voltage and/or other auxiliary power
problems, and blow various components in the low voltage power supply or
elsewhere.

• A simple test to determine if the yoke is at fault for a major geometry
  problem (e.g., a keystone shaped picture) is to interchange the connections
  to the yoke for the axis that is not affected (i.e., the vertical coils if
  the width is varying from top to bottom). If the raster/picture flips
  (indicating that you swapped the proper connections) but the shape of the
  raster remains the same – the geometry is unchanged, the problem is almost
  certainly in the deflection yoke.
• Where high voltage (and other flyback derived voltages) are reduced and
  other problems have been ruled out, unplugging the deflection yoke (assuming
  no interlock) may reveal whether it is likely at fault. If this results in
  high voltage and a relatively clean deflection waveform or returns the power
  supply or deflection chip load to something reasonable, a defective yoke is
  quite possible.

  CAUTION: powering a TV or monitor with a disconnected yoke must be done with
  care for several reasons:

  • The CRT electron beam(s) will not be deflected. If it turns out that the
    yoke is the problem, this may result in a very bright spot in the center
    of the screen (which will turn into a very dark permanent spot quite
    quickly) :-(. Disconnecting only the winding that is suspect is better.
    Then, the other direction will still scan resulting in a very bright line
    instead of a super bright spot. In any case, make sure the brightness is
    turned all the way down (using the screen/G2 control on the flyback if
    necessary). Keep an eye on the front of the screen ready to kill power at
    the first sign of a spot or line. Disconnecting the CRT heater as an
    added precaution would be even better unless you need to determine if
    there is a beam.
  • Removing the yoke (which is effectively in parallel with the flyback)
    increases the inductance and the peak flyback voltage on the HOT. In the
    extreme, this may blow the HOT if run at full line voltage/normal B+. It
    is better to perform these tests using a Variac at reduced line voltage if
    possible.
  • The deflection system will be detuned since the yoke inductance plays a
    very significant role in setting the resonance point in most designs.
    Don’t expect to see totally normal behavior with respect to high voltage.
    However, it should be much better than with the faulty yoke.
• If possible, compare all measurements with a known good identical
  deflection yoke. Of course, if you have one, swapping is the fastest surest
  test of all! In many cases, even a not quite identical yoke will be close
  enough to provide useful information for testing. However, it must be from
  a similar piece of equipment with similar specifications – size and scan
  range. Don’t expect a color TV yoke to work in a high performance SVGA
  monitor!

  Note: the substitute yoke doesn’t have to be mounted on the CRT which would
  disturb purity and convergence adjustments but see the caution above about
  drilling holes in the CRT face plate!

The deflection yoke consists of the horizontal coils and vertical coils (wound
on a ferrite core), and mounting structure. Little magnets or rubber/ferrite
strips may be glued in strategic locations. DO NOT disturb them! In rare
instances, there may be additional coils or other components mounted on the
same assembly. The following deals only with the actual deflection coils
themselves – the other components (if any) can be tested in a similar manner.

Where the test procedure below requires removal of the yoke, see the section:
Removing and replacing the deflection yoke first.

• Horizontal – the horizontal section consists of an even number of windings
  hooked up in parallel/interleaved with half of the windings on each of the
  two ferrite core pieces.

  The horizontal windings will be oriented with the coil’s axis vertical and
  mounted on the inside of the yoke (against the CRT neck/funnel). They may be
  wound with thicker wire than that used for the vertical windings.

  • Resistance check – This may be possible without removing the yoke from
    the CRT if the terminal block is accessible. Disconnect the individual
    windings from each other and determine if the resistances are nearly
    equal. Check for shorts between windings and between the horizontal and
    vertical windings as well.

    Typical resistance of the intact windings (at the yoke connector assuming
    no other components): TV or NTSC/PAL monitor – a few ohms (3 ohms typical),
    SVGA monitor – less than an ohm (.5 ohms typical).

  • Inspection – Look for charring or other evidence of insulation breakdown
    due to arcing or overheating. For the horizontal windings, this will
    require removing the yoke from the CRT since little if any of the windings
    are visible from the outside. However, even then, most of the windings
    are hidden under layers of wire or behind the ferrite core.
  • Ring test. See the document “Testing of Flyback (LOPT) Transformers”.
    This deals with flyback transformers but the principles are the same.
    Disconnecting the windings may help isolate the location of a fault.
    However, for windings wound on the same core, the inductive coupling
    will result in a short anywhere on that core reducing the Q.
• Vertical – The vertical section is usually manufactured as a pair of
  windings wired in parallel (or maybe in series) though for high vertical
  scan rate monitors, multiple parallel/interleaved windings are also possible.

  The vertical windings will be oriented with the coil’s axis horizontal and
  wound on the outside of the yoke. The wire used for the vertical windings
  may be thinner than that used for the horizontal windings.

  • Resistance check – This may be possible without removing the yoke from
    the CRT if the terminal block is accessible. Disconnect the individual
    windings from each other and determine if the resistances are nearly
    equal. Check for shorts between windings and between the horizontal
    and vertical windings as well.

    Typical resistance of the intact windings (at the yoke connector assuming
    no other components): TV or NTSC/PAL monitor – more than 10 ohms (15 ohms
    typical), SVGA monitor – at least a few ohms (5 ohms typical).

  • Inspection – Look for charring or other evidence of insulation breakdown
    due to arcing or overheating. The accessible portions of the vertical
    windings are mostly visible without removing the yoke from the CRT.
    However, most of the windings are hidden under layers of wire or behind
    the ferrite core.
  • Ring test – Since the vertical windings have significant resistance and
    very low Q, a ring test may be of limited value.

Deflection yoke repair

So you found a big black charred area in/on one of the yoke windings. What
can be done? Is it possible to repair it? What about using it for testing
to confirm that there are no other problems before ordering a new yoke?

If the damage is minor – only a few wires are involved, it may be possible to
separate them from each other and the rest of the winding, thoroughly clean
the area, and then insulate the wires with high temperature varnish. Then,
check the resistances of each of the parallel/interleaved windings to make
sure that you caught all the damage.

Simple plastic electrical tape can probably be used for as insulation for
testing purposes – it has worked for me – but would not likely survive very
long as a permanent repair due to the possible high temperatures involved.
A new yoke will almost certainly be needed.

Testing of flyback (LOPT) transformers

How and why do flyback transformers fail?

Flybacks fail in several ways:

1. Overheating leading to cracks in the plastic and external arcing. These
   can often be fixed by cleaning and coating with multiple layers of high
   voltage sealer, corona dope, or even plastic electrical tape (as a
   temporary repair in a pinch).
2. Cracked or otherwise damaged core will effect the flyback characteristics
   to the point where it may not work correctly or even blow the horizontal
   output transistor.
3. Internal shorts in the FOCUS/SCREEN divider network, if present. One sign
   of this may be arcover of the FOCUS or SCREEN sparkgaps on the PCB on the
   neck of the CRT.
4. Internal short circuits in the windings.
5. Open windings.

More than one of these may apply in any given case.

First, perform a careful visual inspection with power off. Look for cracks,
bulging or melted plastic, and discoloration, Look for bad solder connections
at the pins of the flyback as well. If the TV or monitor can be powered
safely, check for arcing or corona around the flyback and in its vicinity,

Next, perform ohmmeter tests for obvious short circuits between windings,
much reduced winding resistances, and open windings.

For the low voltage windings, service manuals may provide the expected
DC resistance (SAMs PhotoFact, for example). Sometimes, this will change
enough to be detected – if you have an ohmmeter with a low enough scale.
These are usually a fraction of an ohm. It is difficult or impossible to
measure the DC resistance of the HV winding since the rectifiers are usually
built in. The value is not published either.

Caution: make sure you have the TV or monitor unplugged and confirm that
the main filter capacitor is discharged before touching anything! If you
are going to remove or touch the CRT HV, focus, or screen wires, discharge
the HV first using a well insulated high value resistor (e.g., several
M ohms, 5 W) to the CRT ground strap (NOT signal ground. See the section:
Safe discharging of capacitors in TVs and video
monitors.

Partially short circuited windings (perhaps, just a couple of turns)
and sometimes shorts in the focus/screen divider will drastically lower
the Q and increase the load the flyback puts on its driving source with
no outputs connected. Commercial flyback testers measure the Q by
monitoring the decay time of a resonant circuit formed by a capacitor and
a winding on the flyback under test after it is excited by a pulse
waveform. It is possible to easily construct testers that perform a
well. See the companion document “Testing of Flyback (LOPT) Transformers”
for further information.

Picture size suddenly becomes larger (or smaller)

You are playing your favorite game (read: addiction) and suddenly, the
picture size increases by 20% and the brightness may have changed as
well. What part should I replace? I only used my phasers on the #3
setting!

Unfortunately, I do not have a crystal ball. There are a number of parts
that could be faulty and no way of know for your monitor and your symptoms
which it is. Sorry, you will almost certainly have to have it professionally
repaired or replaced.

What it sounds like is happening is that the circuitry that selects internal
components depending on scan rate have failed in some way. They could be
making an incorrect selection or the power supply could be faulty and applying
an incorrect voltage to the horizontal and vertical deflection circuits. The
brightness changes since it is not compensated for properly.

Burning up of various size or centering resistors

Check the capacitors that couple the yoke to to ground. If they become
reduced in value or develop a high ESR, the current will be diverted to other
components with unfortunate and rapid consequences.

Picture shifted horizontally

The first thing to determine is if this is a position or phase problem:

• A fault with horizontal position means that the entire raster is shifted
  left or right. This is almost certainly a monitor problem. If you turn
  up the brightness control, the edges of the scan lines will probably be
  visible on one side.
  • Assuming the position or centering controls do not work at or or have
    insufficient range, check for a defective centering pot and bad centering
    diodes and other components in their vicinity. If digitally controlled,
    you will probably need a schematic to find the cause.
  • If the monitor was dropped, the yoke or other assembly on the CRT neck
    may have shifted (though there would probably be other symptoms as well).
  • Monochrome monitors have centering rings on the CRT neck which may have
    be knocked out of adjustment. Color monitors adjust the centering
    electronically since magnetic rings would mess up the purity and/or
    convergence.
• A fault with horizontal phase means that the raster is still centered on
  the screen but the picture itself is shifted (and may have some wrap-around)
  within the raster. This could be a fault in the monitor or video card or
  incorrect settings in the software setup for the video card.
  • If this happened while trying out this monitor on a different or modified
    computer, just after you have done a software upgrade, or just after
    something strange happened (like your PC’s CMOS settings got corrupted –
    monitor settings are generally not in the CMOS setup but may have been
    affected at the same time), reset the monitor’s controls to their default
    or middle position and then use the software setup or install program that
    came with your video card to set scan rates, size, position, and sync
    polarity.
  • Some monitors have a user accessible horizontal phase control in addition
    to horizontal position. This adjusts the delay in the sync circuits so
    check that area of the electronics if the control doesn’t work or have
    enough range.
• There could also be a problem with base drive to the HOT. This may result
  in position, phase, size, and linearity errors as the scan being initiated
  too soon or too late.

Horizontal or vertical flipped picture

The picture is flipped left-to-right or is upside-down or both. This
cannot happen as a result of a failure. For a CRT-based TV or monitor,
it almost certainly means that the wires to the horizontal or vertical
deflection yoke have been swapped to enable the picture to appear
correct when viewed via a mirror (horizontal only) or if the unit
were mounted base-up to a ceiling (both). The remedy is simply to
swap the two wires to the relevant deflection yoke(s). There may
even be obvious splices to guide you. There is usually a connector
with 4 relatively fat wires that go to the deflection yoke on the
CRT neck (NOT the PCB attached to the tube base). If you don’t
have a schematic, trace these on the main PCB back to their origin.
The horizontal will originate somewhere in the vicinity of the flyback
transformer. It may be possible to disengage the wires from
the connector shell and swap them there. If not, cut, splice, and solder.
Adjustment of the appropriate centering controls may be needed.

For flat panel displays, it is even more unlikely this would happen as a
result of a hardware failure. Most likely, there is a mode setting in the
one of the setup menus for the TV or monitor itself. It could also be in
the receiver for the TV, or the driver or application software of the PC.
If the source is a video projector, the menu setting is likely there,
to select between front and rear projection (horizontal) or table or ceiling
mount (both). So, don’t bother to open up the flat panel TV or monitor.
The problem is not there! 🙂

High Voltage Power Supply Problems

Identifying HV voltage problems

In addition to the obvious “monitor screen is as black as a coal mine”
symptom, problems in the high voltage power supply can result in a variety
of brightness, raster geometry, and other picture problems as well as
arcing, corona, or other sights, sounds, and smells not normally associated
with a properly functioning monitor. This chapter deals with some of these.
Other video related problems will be dealt with in the chapter: “Raster,
Color, and Video Problems”.

High voltage power supply fundamentals

Most, monitors derive the high voltage for the CRT second anode (THE high
voltage, focus, and (sometimes) screen (G2) from the horizontal deflection
system. This technique was developed quite early in the history of commercial
TV and has stuck for a very simple reason – it is very cost effective. A
side effect is that if the horizontal deflection fails and threatens to
burn a (vertical) line into the CRT phosphors, the high voltage dies as well.
Of course, if the vertical deflection dies….

Some auto-scan monitors utilize a separate high voltage supply. One reason
for this approach is to decouple the horizontal deflection from the HV
in auto-scan monitors thus simplifying the design.

Usually it is a self contained inverter module. It if can be opened, then
repair may be possible. With a separate HV supply, there is no need for a
HV flyback transformer on the mainboard. Some designs may use a separate HV
supply including a flyback which is part of the mainboard but is self
contained and independent of the horizontal deflection system.

Most TV and monitor (flyback) high voltage supplies operate as follows:

1. Horizontal output transistor (HOT) turns on during scan. Current increases
   linearly in primary of flyback transformer since it appears as an
   inductor. Magnetic field also increases linearly. Note: flyback is
   constructed with air gap in core. This makes it behave more like an
   inductor than transformer as far as the primary drive is concerned.
2. HOT shuts off at end of scan. Current decreases rapidly. Magnetic field
   collapses inductively coupling to secondary and generates HV pulse.
   Inductance and capacitance of flyback, snubber capacitors, and parasitic
   capacitance of circuitry and yoke form a resonant circuit. Ideally,
   voltage waveform across HOT during flyback (retrace) period will be a
   single half cycle and is clamped by damper diode across HOT to prevent
   undershoot.
3. Secondary of flyback is either a single large HV winding with HV rectifiers
   built in (most often) or an intermediate voltage winding and a voltage
   multiplier (see the section: What is a tripler?).
   The output will be DC HV pulses.
4. The capacitance of the CRT envelope provides the needed filtering to
   adequately smooth the HV pulses into a DC voltage. Sometimes there is
   a separate HV capacitor as well.
5. A high resistance voltage divider provides the several kV focus voltage
   and sometimes the several hundred volt screen (G2) voltage as well.
   Often, the adjustments for these voltages are built into the flyback.
   The focus and screen are generally the top and bottom knobs, respectively.
   Sometimes they are mounted separately. This or a similar divider may
   also provide feedback to control high voltage regulation.

What is a tripler?

In some TVs and monitors, the flyback transformer only generates about 6-10 kV
AC which is then boosted by a capacitor-diode ladder to the 18-30 kV needed
for modern color CRTs. The unit that does this is commonly called a tripler
since it multiplies the flyback output by about 3 times. Some TVs use a
quadrupler instead. However, many TVs and monitors generate the required
HV directly with a winding with the required number of turns inside the
flyback transformer.

Triplers use a diode-capacitor ladder to multiply the 6-10 kV AC to 18-30 kV
DC. Many triplers are separate units, roughly cubical, and are not repairable.
Some triplers are built in to the flyback – it is probably cheaper to
manufacture the HV diodes and capacitors than to wind a direct high voltage
secondary on the flyback core. In either case, failure requires replacement
of the entire unit.

For external multipliers, the terminals are typically marked:

• IN – from flyback (6-10 kV AC).
• OUT – HV to CRT (20-30 kV DC).
• F – focus to CRT (2-8 kV).
• CTL – focus pot (many megohm to ground).
• G, GND, or COM – ground.

Symptoms of tripler failure are: lack of high voltage or insufficient high
voltage, arcing at focus protection spark gap, incorrect focus voltage, other
arcing, overload of HOT and/or flyback, or focus adjustment affecting
brightness (screen) setting or vice-versa. Where there is overloading, if you
disconnect the tripler and everything else comes back to life (obviously,
there will be no HV or picture), then it is very likely bad.

High voltage shutdown due to X-ray protection circuits

A monitor that runs for a while or starts to come on but then shuts down may
have a problem with the X-ray protection circuitry correctly or incorrectly
determining that the high voltage (HV) is too great (risking excessive
X-ray emission) and shutting everything down.

A side effect of activation of this circuitry is that resetting may require
pulling the plug or turning off the real (hard) power switch.

Was there anything else unusual about the picture lately that would indicate
an actual problem with the HV? For example, has it suddenly gotten brighter
than normal or has the size decreased? If this is the case, then there may be
some problem with the HV regulation. If not, the shutdown circuit may
be overly sensitive or one of its components may be defective – a bad
connection of leaky cap (or zener).

If the horizontal frequency is not correct (probably low) due to a faulty
horizontal oscillator or sync circuit or bad horizontal hold control (should
one exist!), HV may increase and trigger shutdown. Of course, the picture
won’t be worth much either! With a multiscan monitor, this could happen if the
mode switching is faulty resulting in incorrect component settings for a
given scan rate. A symptom might be HV shutdown when switching into scan
ranges.

The HV shutdown circuit usually monitors a winding off of the flyback
for voltage exceeding some reference and then sets a flip flop shutting
the horizontal drive off.

On some Sony models, a HV resistive divider performs this function and these
do fail – quite often. The red block is often called a ‘HV capacitor’ (but
is technically the ‘HSTAT’ unit because it has a control for horizontal
static convergence) and is a common cause of immediate or delayed shutdown on
certain Sony monitors and TVs. With these failures, the HV doesn’t become
excessive but the sense voltage rises due to leakage with the voltage divider.
See the section: Apple/Sony monitor dies after variable
length of time.

Excessive low voltage supply may trigger high voltage shutdown

(From: Ray Chandos (rchandos@ivc.edu).)

Modern television receivers and video monitors are all equipped with a
safety circuit to shut down the high voltage feeding the anode of the
picture tube if that high voltage becomes excessive. (This is to prevent
dangerous x-rays emitted when electrons with too much energy strike the
metal shadow mask just inside the TV screen.) Unfortunately, high voltage
shutdown problems can be very difficult to diagnose because, once shutdown
has occurred, the horizontal pulses used to generate the high voltage are
turned off, and with them the high voltage itself.

In many cases I have encountered, the high voltage is not excessive, but
the shutdown circuit itself has failed and falsely triggers. A common
cause of this is failure of the circuitry that samples the high voltage and
feeds a portion back to the input of the shutdown circuit. Typically, a
tap from the flyback transformer feeds a diode and a filter capacitor to
produce a sample DC voltage proportional to the high voltage. As the high
voltage increases, so does this sample. It is usually further reduced by a
voltage divider, then sent through a series zener diode to the “horizontal
shutdown” input of a video processor chip, so that, if the divided down
voltage exceeds the rating of the zener diode, the latter will conduct and
trigger the shutdown input, which then latches off the horizontal pulses.
Now if the bottom resistor in the voltage divider opens, or increases above
its nominal value (common for high value carbon resistors), the sampled
voltage will increase, possibly enough to falsely trip the shutdown input.
Check it with an ohmmeter.

Incidentally, if you don’t have a schematic, you can still attempt to
diagnose and repair your shutdown problem. Start with the video processor
IC, a huge chip that controls most of the TV functions. Get the pinout
from this web site, the ECG semiconductor replacement guide, or data sheet
archives on the Internet. Find the horizontal output and horizontal
shutdown pins, and attach oscilloscope probes to verify that you have a
shutdown problem. If you do, you will see horizontal pulses for a brief
instant on power up, but suddenly disappearing as the shutdown input
voltage goes up and turns them off. (This is a latching circuit, so the
shutdown voltage will normally stay high until the power is turned off.)

Now trace the shutdown signal voltage back through the voltage divider, the
filter capacitor, and the diode to the flyback winding. Test out all these
parts as you go.

If the shutdown circuitry all seems OK, it may be doing its intended job of
detecting and disabling excessively high voltage. Too much high voltage
often results when the lower voltage DC supply feeding the high voltage
supply circuitry somehow gets too high. This voltage, often around +160
VDC, nowadays comes from the TV’s main regulated power supply and is
applied to one end of the flyback transformer primary. The other end
connects to the collector of the horizontal output (a large, high voltage
power transistor on a heat sink), the emitter of which connects to ground.
Horizontal drive pulses originating in the video processor circuit drive
the base terminal of this transistor, switching it on when the pulses are
high and thus supplying current to the flyback transformer primary. The
secondary winding, having many more turns, steps up the +160 Volts applied
to the primary to 25 – 45 kV, which is rectified, filtered, and applied to
the anode of the picture tube. Now if the +160 Volts increases, say to
+200 Volts, due to some malfunction in the main power supply regulation,
then the secondary voltage will also increase by the same percentage, and
trip the high voltage shutdown circuit.

Fortunately, although the high voltage quickly vanishes after shutdown,
preventing you from measuring it, the low voltage usually stays on. You
can measure it (carefully) from the collector of the horizontal output
transistor to ground. Of course, if you lack a schematic, you won’t know
if this voltage is correct or not, so again trace it back from the flyback
transformer primary to the main TV power supply. There you may find a
label printed on the printed circuit board telling you the normal voltage.
You can also get a clue by looking at the voltage rating of any filter
capacitor connected from this voltage line to ground. For example, if the
filter capacitor is rated at 200 V and you are measuring 220 V, you know
you have a problem. Sometimes the voltage will come from a linear voltage
regulator IC whose pinout and output voltage you can look up from the chip
number. These linear regulators can short from input to output, raising
the output voltage and leading to the shutdown problem.

If the low voltage comes instead from a switching regulated supply and you
can’t readily determine the normal output voltage, check for a bad filter
capacitor on the feedback winding. Most such power supplies put out
several regulated voltages, derived from separate windings on the switching
supply transformer, then rectified and filtered, for use in various places
in the set. Regulation of these voltages is accomplished by sampling the
output from a dedicated feedback winding, and then cranking up the
transistor switch if that voltage is too low, or cutting back the
transistor switch if the voltage is too high. The idea is that, since all
of the output voltages come from the same transformer, with the output
voltage of each determined by the number of turns on its winding of the
transformer, if one voltage (from the feedback winding)is correct, then
they all will be correct. Now if the filter capacitor on the feedback
winding opens, lowering the sensed DC voltage from that winding, what will
the voltage regulator circuit do? Not realizing that the reduced feedback
is due to a bad filter capacitor, it simply cranks up the transistor switch
to get the voltage back up where it belongs. But that raises all the other
output voltages as well, making them higher than they should be, including
the one powering the high voltage supply! And that will trip the shutdown
circuit.

When replacing filter capacitors, be sure to use good ones rated for 105
(not 85) degrees C, and able to withstand the high frequency pulses they
are getting hammered by in these circuits.

Low or no high voltage

Most of these problems are due to faults in the horizontal deflection
system – shorted HOT, shorted windings or HV rectifiers in the flyback,
defective tripler, or other bad parts on the primary side of the flyback.

In addition, with auto-scan monitors, the incorrect voltage or other
component could be selected due to a logic fault or a problem with the
selection relay or other circuitry.

However, if you discover an inch layer of filth inside the monitor, the HV
could simply be shorting out – clean it first.

In most cases, these sorts of faults will put an excessive load on the
horizontal output circuits so there may be excessive heating of the HOT
or other components. You may hear an audible arcing or sizzling sound from
internal shorts in the flyback or tripler. Either of these may bet hot,
crack, bulge, or exhibit visible damage if left on with the fault present.

Many modern monitors do not regulate HV directly but rather set it via
control of the low voltage power supply to the HOT (B+), by snubber
capacitors across the HOT, and the turns ratio of the flyback. The
HV is directly related to the B+ so if this is low, the HV will be low
as well. Faulty snubber capacitors will generally do the opposite – increase
the HV and the X-ray protection circuits may kick in. However, low HV
is also a possibility. The only way the turns ratio of the flyback can
change is from a short which will manifest its presence in other ways as
well – excessive heating and load on the horizontal output circuits.

While a shorted second anode connection to the CRT is theoretically
possible, this is quite unlikely (except, as noted, due to dirt).

Excessive high voltage

Any significant increase in HV should cause the X-ray protection circuits
to kick in and either shut down the set or modify the deflection in such
a way as to render it harmless.

Symptoms include arcing/sparking of HV, smaller than normal picture, and
under certain scenarios, possible excessive brightness.

Causes of the HV being too high are:

1. Excess B+ voltage to the HOT. The likely cause is to a low voltage
   regulator failure.
2. Open snubber capacitors across the HOT. These are under a lot of
   stress and are located near hot components so failure is possible.
3. Incorrect excessively long scan drive to HOT caused by failure of
   horizontal oscillator/sync circuits. However, other things like the
   HOT will probably blow up first. The picture will definitely be
   messed up. This is more likely with auto-scan monitors than TVs
   since what is too long for one scan range may be correct for another
   and the selection circuitry is confused or broken.
4. Failure of HV regulator. Actual HV regulators are uncommon today but
   the HV may controlled by a feedback voltage from a divider (focus or
   screen, or its own) or a secondary winding on the flyback setting the
   B+ or drive timing. This may result in an underscanned (smaller than
   normal) picture if only the HV and not the deflection voltages as well
   are derived from the same supply.

In one example of (4), a arcing of the HV in a Conrac studio monitor resulted
in the destruction of the HV switchmode inverter transistor (this used
a separate HV supply) and a fusable resistor. The cause was an open HV
feedback resistor divider allowing the HV to increase drastically.

Snaps, crackles, and other HV breakdown

Various problems can result in occasional or sustained sparking or arcing
sounds from inside the monitor. Note that a static electricity buildup
is common on the front of the screen. It is harmless and there iss nothing
you can do about it anyhow.

The following may result in occasional or sustained sounds not commonly
associated with a properly working TV or monitor. There may or may not be
flashes or blanking of the screen at the same time as the audible noise.
See the same-named sections that follow for details.

• Arcing, sparking, or corona from CRT HV anode (red wire/suction cup).
• Arcing at CRT sparkgaps.
• Arcing from flyback or vicinity.
• Arcing due to bad connections to or disconnected CRT return.
• Flashovers inside the CRT.

Arcing, sparking, or corona from CRT HV anode (red wire/suction cup)

Symptoms could include a sizzling corona or more likely, an occasional
or rapid series of sharp snaps – possibly quite loud and quite visible – from
the anode cap on the CRT to the grounded coating on the outside of the CRT or
a chassis ground point (or any other conductor nearby). Corona is a high
resistance leakage through the air without total breakdown. The snapping
is caused by the sudden and nearly complete discharge of the CRT anode
capacitance through a low resistance ionized path similar to lightning.

There are two likely causes:

1. Dirt, dust, grime, around and under the suction cup on the CRT are
   providing a discharge path. This may be more severe in humid weather.
   Safely discharge the HV and then remove and thoroughly clean the HV
   suction cup and the area under it and on the CRT for several inches
   around the HV connection. Make sure there are no loose wires or other
   possible places for the HV to discharge to in the vicinity.
2. The high voltage has gone through the roof. Usually, the X-ray protection
   circuitry should kick in but it can fail. If cleaning does not help,
   this is a likely possibility. See the sections:
   High voltage shutdown due to X-ray protection
   circuits and Excessive high voltage.

Arcing at spark gaps and gas discharge tubes on CRT neck board or elsewhere

These are protective devices intended to breakdown and divert excessive voltage
away from the CRT (usually).

This is rarely due to a defective sparkgap or gas discharge tube but rather is
a safety mechanism like a fuse designed to protect the internal electrodes of
the CRT if the focus or screen voltage should become excessive. The sparkgap
breaks down first and prevents internal arcing in the CRT. These sparkgaps
may be built into the CRT socket as well.

Arcing at a sparkgap or a glowing or flashing discharge tube may be accompanied
by total loss of picture or bad focus, brightness or focus fluctuations, or
any of a number of similar symptoms. A common cause is a breakdown inside the
focus divider (usually part of the flyback or tripler) but could also be due to
excessive uncontrolled high voltage due to a failure of the B+ regulator or HOT
snubber capacitor, or (ironically) even a short inside the CRT.

• Spark gaps may be actual two or three pin devices with seemingly no
  insides, part of the CRT socket, or printed on the circuit board itself.
• Gas discharge tubes look like small neon lamps (e.g., NE2) but could be
  filled with some other gas mixture to provide a controlled higher breakdown
  voltage.

Therefore, like a fuse, don’t just replace or disable these devices, locate and
correct underlying problem. The CRT makes an expensive fuse!

Spark gaps and gas discharge bulbs on CRT neck board or elsewhere

These are protective devices intended to breakdown and divert excessive voltage
away from the CRT (usually).

• Spark gaps may be actual two or three pin devices with seemingly no insides
  or printed on the circuit board itself.
• Gas discharge bulbs look like small neon lamps (e.g., NE2) but could be
  filled with some other gas mixture to provide a controlled higher breakdown
  voltage.

Arcing at a spark gap or a flashing or glowing gas discharge tube may indicate
excessive high voltage, a short in the focus/screen divider network of the
flyback, a short in the CRT, or some other fault resulting in abnormally high
voltage on its terminals.

Arcing from flyback or vicinity

Arcing may be visible or audible and result in readily detectable levels
of ozone. Note that very slight traces of ozone may not indicate anything
significant but if the TV smells like an office copier, there is probably
some discharge taking place.

WARNING: It is possible for arcing to develop as a result of excessive high
voltage. Symptoms might be a smaller than normal excessively bright picture
but this may not be able to be confirmed until the flyback is repaired or
replaced. See the section: Excessive high voltage.

• On the HV output, it will probably be a loud snapping sound (due to the
  capacitance of the CRT) with associated blue/white sparks up to an inch or
  more in length. If the arc length is short enough, this may turn into a
  nearly continuous sizzling sound with yellow/orange arc and melting/burning
  plastic.
• Prior to the HV rectifier, it will likely be a continuous sizzle with
  orange/yellow/white arc and melting/burning plastic or circuit board
  material.
• Internal arcing in the flyback may be audible and eventually result in
  a bulging and/or cracked case (if some other component doesn’t fail first
  as this would take some time to develop).
• A corona discharge without actual sparks or a visible well defined arc
  is also possible. This may be visible in a totally dark room, possibly
  more likely when the humidity is high. A thorough cleaning to remove all
  dust and grime may be all that is needed in this case.
• If the arc is coming from a specific point on the flyback – a crack or
  pinhole – this may be patched well enough to confirm that the rest of the
  monitor is operational and a new flyback is worth the money. Otherwise,
  there is no way of knowing if the arcing may have damaged other circuitry
  until a replacement flyback – possibly money wasted – arrives.

  To attempt a repair, scrape off any dirt or carbon that is present along the
  path of the arcing and its vicinity. Then, clean the area thoroughly with
  alcohol and dry completely. Otherwise, the dirt and carbon will just act as
  a good conductor and the arcing will continue under your repair! Several
  layers of plastic electrical tape may be adequate for testing. Multiple
  coats of high voltage sealer or non-corroding RTV silicone (if it smells like
  vinegar – acetic acid – as it cures, this may get in and affect the windings)
  would be better if the objective is an actual repair. A thick layer of
  Epoxy may be even better and affected less by possible HV corona. Either of
  these may prove to be a permanent fix although starting the search for a
  source for a new flyback would not hurt just in case. The arc most likely
  did damage the insulation internally which may or may not be a problem in
  the future.

  Also see the section: Dave’s complete procedure for
  repair of an arcing flyback.

• In some cases, the pinhole or crack is an indication of a more serious
  problem – overheating due to shorted windings in the flyback or excessive
  secondary load.
• If the arc is from one of the sparkgaps around the CRT, the CRT socket,
  or the plastic ‘alignment base’ on the CRT itself, this could also be a
  flyback problem indicating internal shorts in the focus/screen network.
• If the arcing is inside the CRT, this could indicate a bad CRT or a problem
  with the flyback focus/screen network and no or inadequate sparkgap
  protection.

Where repair seems possible, first, clean the areas around the arc thoroughly
and then try several layers of plastic electrical tape. If the TV works
normally for say, an hour, then there is probably nothing else wrong and you
can try for a proper sealing job or hope that tape holds out (put a few more
layers on – each is good for about 8-10 kV theoretically).

Once I had a TV where the main problem was a cracked flyback arcing
but this took out one of the fusable resistors for the power supply to
the *vertical* output so the symptoms included a single horizontal line.
Don’t ask me to explain – replacing that resistor and the flyback (the
flyback tested good, but this was for someone else) fixed the TV.

In another case, a pinhole developed in the flyback casing probably
due to poor plastic molding at the time of manufacture. This resulted in
a most spectacular case of sparking to a nearby bracket. A few layers of
electrical tape was all that was needed to affect a permanent repair.

However, replacement is really the best long term solution both for reliability
as well as fire risk.

(From: Bert Christensen (rosewood@interlog.com).)

It may well last a long time. The insulation breakdown was probably in the
area of the rectifier section rather than the flyback section. I have repaired
several units in the same way but I have generally replaced the flyback before
sending back to the customer. I am worried that the repair will not hold and
that a fire could start. I have no desire whatsoever to be sued by some fire
insurance company.

I am always reminded by the experience that Zenith had with its System 3
chassis a few years ago. They burned and caused many house fires including
one in the governor’s mansion in Texas. Zenith spent mega bucks on that one.
They also spent mega-bucks on their ‘safety capacitor’ mess a few years
before that.

Dave’s complete procedure for repair of an arcing flyback

(From: Dave Moore (penguin@datastar.net).

First I clean the afflicted area with Electromotive spray from Autozone. It’s
for cleaning alternators. On Z-line I remove the focus control and wash with
the alternator cleaner and a tooth brush until all dirt and carbon deposits
are removed. Then I take an xacto knife and carve out the carbonized hole
where the arcing broke through. Then take your soldering iron and close the
hole by melting adjacent plastic into it. (clean any solder off your iron with
solder-wick first). Then cut some plastic off of some other part off the
flyback where it wont be needed and use this to plastic weld (with your iron)
a hump of a patch into and over the arc hole. Smooth and seal with iron. Next
apply as thick a layer of silicone rubber as you can and let dry overnight.

Arcing due to bad connections to or disconnected CRT return

The Aquadag coating on the outside of the CRT is the negative plate of the HV
filter capacitor. If this is not solidly connected to the HV return, you will
have your 25 kV+ trying to go where it should not be. There should be a wire
solidly attached to the CRT neck board or chassis. Without this, voltage will
build up until it is able to take some other path – possibly resulting in
damage to sensitive solid state components in the process. Therefore, is is
important to rectify the situation.

Warning: If you find this disconnected, don’t just attach it anywhere. You
may instantly kill ICs or other solid state components. It must be connected
to the proper return point on the CRT neck board or chassis.

Flashovers inside the CRT

Due to sharp edges on the electron gun electrodes, impurities, and other
manufacturing defects, there can be occasional arcing internal to the
CRT. Properly designed HV, deflection, and power supply circuits can
deal with these without failing but not all monitors are designed well.

There is nothing you can do about flashovers assuming your HV is not
excessive (see the section: Excessive high voltage.
If these persist and/or become more frequent, a new CRT or new monitor will
be needed.

Ozone smell and/or smoke from monitor

Smoking is just as bad for monitors as for people and usually more quickly
terminal (no pun….).

White acrid smoke may indicate a failed electrolytic capacitor in the
power supply probably in conjunction with a shorted rectifier. Needless to
say, pull the plug at once.

A visual inspection should be able to easily confirm the bad capacitor as it
will probably be bulging and have condensed residue nearby. Check the
rectifier diodes or bridge rectifier with an ohmmeter. Resistance across
any pair of leads should be more than a few ohms in at least one direction.
Remove from the circuit to confirm. Both the faulty diode(s) and capacitor
should be replaced (though the capacitor may work well enough to test
with new diode(s).

If a visual inspection fails to identify the smoking part, you can probably
plug the monitor in for a few seconds until the source of the smoke is obvious
but be prepared to pull the plug in a real hurry.

If the smell/smoke is coming from the flyback, then it has probably gone
belly up. You may be able to see a crack or bulge in the case. While
the flyback will definitely need to be replaced, it is likely that nothing
else is wrong. However, it might be prudent to use a Variac when performing
initial testing with the replacement just in case there is a secondary
short circuit or excess HV problem.

X-ray and other EM emission from my TV or monitor?

X-ray radiation is produced when a high velocity electron beam strikes
a target containing heavy metals. In a modern TV or monitor, this can only
take place at the shadow mask/aperture grille and phosphor screen of the CRT.

For X-rays, the amount of radiation (if any) will be proportional to
brightness. The energy (determined by the CRT high voltage, called kVP
in the medical imaging field) is not affected. This is one reason many
monitors and TVs are designed with brightness limiting circuits.

In any case, there will be virtually no X-ray emissions from the front of
the CRT as the glass is greater than an inch thick and probably contains
some lead for added shielding. Also see the section:
Should I be worried about X-ray exposure while
servicing a TV or monitor?.

Electromagnetic radiation (EM) is produced mostly from the deflection yoke
and to a lesser extent from some of the other magnetic components like
transformers and inductors. Depending on monitor design (some are
specifically designed to reduce this), EM emissions can vary quite a bit.
Frequencies range from the 50/60 Hz of the power line or vertical scan rate
to several hundred kHz in the AM broadcast band. The intensity and spectral
distribution will vary depending on horizontal and vertical scan rate.

A totally black screen will reduce X-ray emission to zero. It will not
affect EM emissions significantly as most of this comes from the magnetic
parts, particularly the deflection yoke.

There is no measurable microwave, IR, or UV radiation.

I refuse to get into the discussion of what, if any, health problems result
from low level EM emissions. There is simply not enough data.

Should I be worried about X-ray exposure while servicing a TV or monitor?

The only source of X-rays in a modern TV or monitor is from the CRT. X-rays
are generated when a high velocity electron beam strikes a heavy metal target.
For anything you are likely to encounter, this can only happen in a vacuum –
thus inside the CRT. The higher the voltage, the greater the velocity and
potential danger. Really old TVs (prior to around 1975) may still have HV
rectifier and regulator tubes – other sources of X-rays. However, modern TVs
and monitors implement these functions with solid state components.

The thick front CRT faceplate protects users adequately but there may be some
emission from the thinner sides. At 25-30 kV (quite low as X-ray energies go)
X-rays will be stopped by almost any metal so what you have to worry about
is where there are no shields. In addition, the CRT glass usually contains
some lead compounds to block X-ray emissions.

Other than lowering the brightness (or high voltage!), there isn’t anything
you can do to reduce X-ray emission from the front of the monitor. Any sort
of add-on screen (grounded or otherwise) unless it is made of thick leaded
glass, will have no significant effect on X-rays. If you are still concerned,
sit farther away.

However, realistically, there is very little danger. I would not worry about
exposure unless you plan to be sitting for hours on the sides, behind, or
under the TV or monitor – with a picture (there will be none if the screen is
black).

It is interesting that even those 1.5″ Watchman and .5″ camcorder viewfinder
CRTs have X-ray warning labels even though the high voltage used with these
isn’t anywhere near high enough to be of any concern!

More on radiation from TVs and monitors

(From: Jerry Greenberg (jerryg50@hotmail.com).)

Your standard TV set or monitor should not exceed about 0.2 mR/Hr of
radiation from a distance of 5 cm from any part of the cabinet. Most
TV monitor equipment is less than half of this amount.

The CRT has a coating on the inner wall of its glass envelope, and also
there is a metal shadow mask or aperture grill in the front. There is
also a metal shroud around its parameter.

The type of emission from the CRT is known as soft X-Ray emission.
This is because it is low power, and is in the lower X-Ray region.

The X-Ray emission is strongest at the rear of the TV set because there
is some opened area where the electron gun is located. But, this is
very weak as well. The radiation from a TV or monitor is not being
focused to one point, and is also below the threshold level of being
dangerous.

The long term effect of the total radiation from normal operating TV
equipment is not fully known. However, the effect of X-Ray
radiation is accumulative over time if there are no breaks in between
the exposures. As for standard focused X-Rays like the ones used in a
medical or security facility, these and most of their effects are well
known.

As for normal working TV equipment, when used normally, the total
radiation is less that what you would get when walking on the street.
There are many satellites beaming down signals, radio and TV broadcast
stations, communications systems, and then cell phones.

The X-Ray radiation in a TV set is emitted from the effect of the High
Voltage drive generating the electron beam. If the High Voltage
exceeds the designed safety limit for the CRT, then there is concern
that the X-Ray radiation may have some effect on anyone that is in
close proximity to the CRT. The amount of by which the high voltage
exceeds the design specfifications will determine the total X-Ray emission.
Since this emission is not focused into a fine area, its immediate danger
is also greatly reduced.

All TV sets by law must have in their design some type of protection
to shut the TV down if there is excessive High Voltage, excessive High
Voltage current drive, and a number of other safety criterias.

There is also the concern about electromagnetic radiation. In fact all
radio frequencies are based on electromagnetic radiation (EMR).

There was a great concern about the low frequency EMR. This would come
from the power supply, deflection amplifier stages, and then from the
deflection yoke and flyback transformer. There different types of EMR
from TV sets.

Concerning TV’s and monitors, this radiation worry comes up from time to
time. If a woman is pregnant it would be wiser for her to not expose
the unborn baby by working close to a terminal or monitor. This
nonexposure is a good policy to make sure that everyone is safe rather
than suffer any type of damage or health risks.

As for a safety concern for a mother to be, or a small baby, they can
be in front of a TV set but at least 5 to 7 feet away. From this
distance there should not be any danger at all.

The above is from my personal observations and is very general. I have
also read various publications over the years that pertain to this
subject.

I have a personal concern about the radiation from TV sets and monitors
because I do an extensive amount of service on these. I am also doing
a lot of picture tube changes in monitor equipment. I am then exposed
for a few hours because I must do the purity and convergence setups of
these sets. I have some days where I work 10 to 12 hours doing TV and
monitor service work.

If you want a TV monitor that will put out near zero X-Ray radiation,
and very low electromagnetic radiation, then go for one of the new LCD
flatscreen monitors.

Flyback got wet

You put your can of Coke where????

Who says these FAQs cannot be funny?

Needless to say, unplug the monitor immediately. Inspect around the target
area for obviously blown or damaged components. Test fuses and fusable
resistors. Remove all traces of liquid – especially sugary or corrosive
liquid. Use water first and then alcohol to promote drying.
Repair burnt solder connections and circuit board traces.
Once the monitor is entirely dried out, power it up – preferably through a
series light bulb and/or Variac until you are sure nothing else will
let loose. Look, listen, and smell for any unusual behavior. If it
now works, then consider yourself lucky. If not, there may be damage
to transistors, ICs, or other components.

Another cause of this is using spray cleaner or a too wet rag on the front
of the CRT (other parts of the monitor, for that matter). Any liquid
which drips inside (all too likely) may short out circuitry on the mainboard
with very expensive consequences.

Blooming or breathing problems

There are several symptoms that are basically similar:

• Blooming is defined as an expansion of the raster or horizontal sections of
  the raster with bright material. For example, switching between dark and
  light picture causes the size of the picture to expand by 10%. A slight
  change in size is unavoidable but if it is greater than 1 or 2 percent from
  a totally black image to a full white one, this is either an indication of a
  defective monitor or one that is badly designed. The cause is poor low or
  high voltage regulation.

  Check the B+ to the horizontal deflection. This is usually well regulated.
  If it is varying in sympathy to the size changes, trace back to determine
  why the low voltage regulator is not doing its job. The reason for the size
  change is that the high voltage is dropping and reducing the stiffness of
  the electron beam.

• Expansion of the raster width in areas of bright imagery is an indication
  of short term regulation problems. The video drive may be interacting
  with the other power supplies. Check for ripple – this would be
  at the vertical scan rate – in the various regulated power supplies.
  The cause may be a dried up electrolytic capacitor – once you locate the
  offending voltage, test or substitute capacitors in that supply.

In both these cases, if this just started after some work was done to the
monitor, the brightness limiter and/or video drive may simply be set so
high that the monitor cannot supply enough current to the high voltage.
If the brightness is acceptable with these turned down slightly and still
have acceptable brightness, then there may be nothing wrong.

• Breathing is defined as a periodic change in the size of the raster which
  may be independent of what is displayed or its severity or frequency may
  be related to the brightness or darkness of the image. This is another type
  of regulation problem and may be caused by bad electrolytic capacitors or
  other components in the low voltage power supplies.

  If the monitor uses a switchmode power supply or low voltage regulator
  separate from the horizontal deflection, first check its output(s) for a
  variation in voltage at the breathing rate. Test with a light bulb or
  resistor load to confirm that the problem is here and not the deflection
  or remainder of the monitor.

• A condition with somewhat similar symptoms is bad focus – fuzzy picture –
  but only with bright (high beam current) scenes. This could be just a matter
  of adjusting the focus control but may also indicate sub-optimal filament
  voltage due to bad connections or components in the filament circuit, or a
  tired worn CRT. You won’t get high beam current without some serious spot
  blooming (a fat beam because too much cathode area is used) and you will get
  cathode ‘poisoning’ after prolonged use.

  Visually inspect the neck of the CRT for the normal orange glow of the
  filaments and check for bad connections and bad parts.

Erratic focus or screen (G2) voltage and/or controls on flyback

Symptoms may include fluctuating focus or brightness. In extreme cases,
the result may be a too bright or dark picture or other behavior caused
by breakdown in the Focus/Screen(G2) divider network.

Usually, this will require flyback replacement to repair reliably. Sometimes,
the section with the controls can be snapped apart and cleaned but this is not
common.

First, just try rotating the screen (G2) control back and forth a few times.
This may clean up the contacts and eliminate the erratic behavior. Possibly,
positioning it a bit to one side of the original location will help. Then,
use the individual or other master background/bias adjustments to compensate
for the improper brightness.

If pressing in on the erratic control helps to stabilize the setting, you
might try adjusting it to the optimal position and then put a dab of hot-melt
glue (or Superglue if you can manage not to stick your fingers together) on
the shaft to hold it with a little more contact force.

If none of this helps, here is a ‘well it’s going in the dumpster anyhow’
procedure to try:

After discharging the CRT (so you don’t get zapped) drill a tiny hole in
the plastic cover near the bad control. Be careful you don’t damage anything
inside – you just want access to the contacts of the controls. Use a hand
drill with, say, a 1/16″ bit. Don’t drill more than about 1/8″ deep which
should enter the airspace. Then spray some contact cleaner through the
hole and work the controls. Wait sufficient time (say, 24 hours) for
everything to dry COMPLETELY and see if behavior changes (or it works at all).

This is a ‘you have got to be kidding’ type of repair so no guarantees :-).

If by some miracle it does work, fill the hole with a drop of RTV or just
put a couple of layers of electrical tape over it.

Focus/Screen divider bypass surgery

This is kludge number 41256 but may be the difference between a bit more life
and the dumpster.

If the previous extreme measures don’t help, then it may be possible to simply
substitute a good divider network externally.

Note that if there is evidence of internal breakdown in the divider of the
original flyback (hissing, cracks, overheating, bulging case, etc.), this will
not work unless you can disconnect it from its HV connection.

There are two issues:

1. Is this a stable situation? Even if you provide an external substitute,
   the parts inside the flyback may continue to deteriorate eventually
   resulting in other more total failure of the flyback or worse.
2. If you provide an external focus/screen divider, it must be done is such a
   manner (including proper mounting and super insulation) such that it cannot
   be called into question should there be a fire where the monitor is even
   the slightest bit suspect.

Various size external focus/screen divider networks can be purchased but
whether this is truly a cost effective solution is not obvious.

(From: Larry Sabo (sabo@storm.ca).)

I just ordered a ‘bleeder resistor’ from Data Display Ltd (Canadian sub of
CCS) to use as a cure for flybacks with flaky focus/screen pots. It contains
focus and screen pots, and costs Cdn$ 16.99, which is a lot less than a
complete flyback, that’s for sure. I expect it will be compatible with quite a
wide range of flybacks.

I have used bleeder resistor assemblies from duff flybacks a couple of times
with good success. You connect the HV lead into the HV cap of the original
flyback, ground all pins of the sub flyback, and use the focus and screen
leads from the sub bleeder assembly in place of the originals.

Looks like hell but works fine. Mounting (and securing) the substitute is a
challenge given the limited space available. I only use this approach on what
would otherwise be uneconomical to repair, and always advise the owner or
customer of the cobbling job. It also enables you to verify whether it is
the flyback that needs replacement, versus the CRT.

Decaying or erratic focus or screen (G2) voltages

The following applies to both CRT focus voltage (which should be a few kV)
and screen or G2 voltage (which should be several hundred V).

“The screen voltage will come up to normal after sitting over night, 400 V or
so. After approximately 5 minutes or slightly longer, I hear a slight arcing.
From that point on, the screen voltage will wander anywhere from 75 V up to
maybe 150 V. Adjustment of the screen control on the flyback has only a small
effect and is not permanent. Removing the CRT pcb results in the screen
voltage returning to normal.”

This is very likely a short between electrodes inside the CRT unless there
is something on the neck board that is breaking down as a result of some
connection to the CRT. The flyback should largely not know the difference
with the socket plugged into the CRT. However, on rare occasions, there is
contamination within the ‘plastic alignment base’ on the end of the CRT
neck. (It is possible to *carefully* remove the plastic piece and clean
the CRT glass/pins. Reinstall the plastic piece if it is still intact
or leave it off – just take care in replacing the CRT neck board.)

One possibility is that glue used to hold components down on some circuit
boards has deteriorated and turned conductive. Check for tan to brown
stuff shorting traces on the CRT neck board. If this is present on the
focus or screen traces or wires, it may just be your problem. Scrape off
all of the old glue and then clean thoroughly. Repair any damaged traces.

What happens to the HV? A HV breakdown possibly inside the CRT would result
in all the voltages being dragged down.

What happens to the picture?

If you connect a charged HV capacitor (guessing a couple hundred volts,
a couple microfarads) between G2 and G1 or focus, you **will** know if
tapping the neck results in a momentary short! I cannot predict whether
this will be a temporary cure or permanent killer. See the section:
Rescuing a shorted CRTRescuing a shorted CRT.

Here is another thing to try: put a 100 M ohm or so resistor between SCREEN
and the CRT socket. This should not affect the behavior much until the
failure occurs. Then, check the voltage on both sides with a high impedance
voltmeter (1000 M). If the CRT is arcing, it will be much lower on the CRT
side and will probably fluctuate. You can play similar games with focus
voltage.

Disconnecting flyback wire(s) from CRT driver board

In some cases, there may be one or more separate wires running to directly
to the CRT socket. These are typically for focus which has a relatively
high voltage so better insulation is needed but there may be no obvious means
of removal should flyback replacement be needed.

One alternative is simply to cut the wire(s) in a location that is well away
from any place to short out, solder, and then do a most excellent job of
insulating the splice. If there is more than one wire, make sure to label
them first if they aren’t color coded.

However, you may find that the cap on the CRT socket snaps off using a thin
knife blade or screwdriver. The wire may be soldered or just pressed in place
in such a way that pulling it out is difficult or impossible without removing
the cover. If there is more than one wire, label them before removal unless
the locations are clearly marked. Sometimes the color is stamped on the
plastic but there may just be a designation like “A” and “B”.

(From: Raymond Carlsen (rrcc@u.washington.edu).)

The last one I worked on puzzled me for a few moments. See if you can see a
space between the little cup (where the wire enters the socket) and the socket
itself. Pry up on the cap with a knife and it should pop right off. The wire
is soldered to a pin under it. Don’t apply heat for very long… you may melt
the socket.

Focus or screen voltage drifts after warmup only when CRT is connected

“I have a 3-5 yr old monitor that loses screen voltage. I believe that the
problem is specific to the CRT or the flyback, either one is a guess I’d
rather be sure of prior to ordering a part.

The screen voltage will come up to normal after sitting over night, 400 V or
so. After approximately 5 minutes or slightly longer, I hear a slight arcing.
From that point on, the screen voltage will wander anywhere from 75 V up to
maybe 150 V. Adjustment of the screen control on the flyback has only a
small effect and is not permanent. Removing the CRT pcb results in the screen
voltage returning to normal.

I cannot find the source of the arcing, as it happens quickly and I have
always been on the other side of the set when it happens. I have replaced
the crt socket, thinking the spark gap was arcing. I have checked the CRT
for G1 and HK shorts on a sencore crt checker, it checks good, but I am aware
that since it is an intermittent problem, that the checker probably will not
catch it.”

This is very likely a short between electrodes inside the CRT unless there
is something on the neck board that is breaking down as a result of some
connection to the CRT. The flyback should largely not know the difference
with the socket plugged into the CRT. However, on rare occasions, there is
contamination within the ‘plastic alignment base’ on the end of the CRT
neck. (It is possible to *carefully* remove the plastic piece and clean
the CRT glass/pins. Reinstall the plastic piece if it is still intact
or leave it off – just take care in replacing the CRT neck board.)

One possibility is that glue used to hold components down on some circuit
boards has deteriorated and turned conductive. Check for tan to brown
stuff shorting traces on the CRT neck board. If this is present on the
focus or screen traces or wires, it may just be your problem. Scrape off
all of the old glue and then clean thoroughly. Repair any damaged traces.

What happens to the HV? A HV breakdown possibly inside the CRT would result
in all the voltages being dragged down.

What happens to the picture?

If you connect a charged HV capacitor (guessing a couple hundred volts,
a couple microfarads) between G2 and G1 or focus, you **will** know if
tapping the neck results in a momentary short! I cannot predict whether
this will be a temporary cure or permanent killer.

Here is another thing to try: put a 100 M ohm or so resistor between SCREEN
(or FOCUS) and the CRT socket. This should not affect the behavior much
until the failure occurs. Then, check the voltage on both sides with a high
impedance voltmeter (>1000 M). If the CRT is arcing, it will be much lower
on the CRT side.

Raster, Color, and Video Problems

Blank picture, power light on, digital controls (if any) active

Does ‘blank picture’ means a totally black screen with the brightness and
contrast controls having no effect whatsoever? Or, is there is no picture
but there is a raster – light on the screen? The direction in which
troubleshooting should proceed differ significantly depending the answer.

Verify that you computer has not simply entered power saving mode and
blanked the screen or shut off the monitor video and power circuits
entirely.

Confirm that the video source is not defective or blank – try another one.

Here are some questions:

1. Is there any light on the screen at any settings of the brightness
   and contrast controls, and/or when switching channels. Can you see any
   raster scanning lines?
2. Can you obtain a raster of any kind by adjusting the screen (G2) control
   (probably on the flyback) or master background or brightness?
3. Looking in the back of the monitor, can you see the glow of the CRT
   filaments?
4. Do you get that static on the front of the tube that would indicate that
   there is high voltage?

If the answer to all of these is ‘no’, then you have a power supply and/or
deflection problem. Refer the the section: No picture
but indications of power.

Possible causes of no raster:

• No or low high voltage (low voltage, deflection, or high voltage power
  supply failure).
• Fault with other voltages like G1 or screen (G2) to CRT.
• Filament to CRT not getting powered.
• Drive to CRT bad/shut off as a result of fault elsewhere. For example,
  failure of the vertical deflection may disable HV or blank the screem to
  protect the CRT from burn-in due to the very bright horizontal line that
  would result. With some monitors, it is possible that the X-ray protection
  circuitry will blank the screen.

Possible causes of no video: problem in video input, video amplifiers, video
output, cutoff due to other fault.

It could be as simple as a bad connection – try gently prodding the boards
with an insulated stick while watching the screen. Check for loose connectors
and reseat all internal connectors.

Brightness control has no effect

The following assumes that the picture is fine but the brightness is
fixed – probably at too high a level. However, there could be several
interrelated problems if a common supply voltage were missing, for example.

If it is a knob, then it should be varying the control grid (G1) voltages
relative to the cathodes (K) of the CRT. This is not likely to be a very
complex circuit. If you do not have a schematic, start by tracing
from the control, check continuity and solder connections. Check the
control itself for proper operation with an ohmmeter. A power supply going
to one side of the control (negative probably) may be missing. Tbe control
grid voltage will end up on the little board on the neck of the CRT – check
there as well for bad solder connections or open resistors.

If brightness is a digital control, then you will need a schematic unless
there is an obvious bad connection.

No color – black and white picture

This means absolutely no color – equivalent to a black and white picture.
Not even a hint of color.

If you are using a composite video input, troubleshoot the chroma circuitry
like you would a TV – see the document: Notes on the
Troubleshooting and Repair of Television Sets.

This is an extremely unlikely failure mode for a computer monitor
unless you are using a composite video input. It is most likely to
a software driver or program problem. Sometimes, the PC will think that
the monitor you have connected is not capable of color and certain programs
will then display in B/W no matter what. This may be due to an initialization
problem – possibly a race condition during the boot process – especially
likely if you are using an older video card with a new fast processor.

First, confirm that the source is actually in color – try the monitor on
another computer or vice-versa.

Check the settings of any mode switches – in rare cases there is a color/mono
switch or button.

Note that to the average person, the obvious question becomes: is my color
picture tube bad? The answer is a definitive NO. It is virtually impossible
for a defective CRT to cause a total loss of color. A defective CRT can
cause a lack of a primary color – R, G, or, B which will mess up the color
but is not likely to result in a black and white picture.

One color is too weak or too strong

If the problem is slight and/or has gradually gotten worse, this may just
require an adjustment of the color brightness/background/bias and/or color
gain/drive controls inside the monitor. See the section:
Brightness and color balance adjustment.

Even if it appears as though there is an excess, this may actually be a
reduction in one of the primary colors. For example, a magenta tinge is
represents a reduction in the strength of the green signal.

• Too high an intensity for one of the color channels will result in a tint
  of one of the primaries: red, green or blue.
• Too low an intensity for one of the color channels will result in a tint of
  the complement of one of the primaries: yellow, cyan, or magenta.
• Problems mainly in the shadows or dark areas of the picture usually
  represent a fault with brightness/bias/background.
• Problems mainly in the highlights or bright areas of the picture usually
  represent a fault with the gain/drive.

A color that that is now suddenly brighter or darker than normal resulting in
incorrect color balance or a tint in the background could be due to a number
of causes:

• Bad cable or pin bent on cable connector.
• Bad connections or bad component in video amplifier or on CRT neck board
  for that color.
• Weak gun in CRT (reduced color).
• Bad video card or incorrect software color map settings.
• For monitors with sync-on-green capability, the monitor may think you are
  using sync-on-green when in fact you have separate sync. In particular,
  this may result in a problem with excessive green:

  (From: Bob Myers (myers@fc.hp.com).)

  Some monitors provide a user-selectable setup option for “sync-on-green”
  vs. separate syncs. Sometimes, this doesn’t really change where the
  sync itself is coming from. In those cases, it’s automatically detected
  but *does* change where the reference level for the video is expected
  to be. You might try checking this setting, if you have it, and changing
  it back and forth to check the effect. It’s not likely to be the problem
  in a separate-sync system like a PC, but weirder things have happened
  and it’s easy and cheap to check out.

Psychodelic color

The means colors that are not normal and that adjustment of the user
controls is not able to correct it so that all colors of the picture
are properly displayed at the same time. For example, you are unable
to get any yellows or blues in picture that should have these colors.

• If you are using a composite video input, troubleshoot the chroma circuitry
  as you would a TV – see the document: Notes on the
  Troubleshooting and Repair of Television Sets.
• Confirm that the input is not a weird color video – try another software
  program or video source. We have a draftsperson who always sets up his
  Windows color scheme in this manner – we keep wishing it is the monitor
  as **that** could be fixed!
• Verify that this is not a missing color problem – one of the primary R, G,
  or B, has disappeared. If so, refer to the section:
  Intermittent, flickering, or missing colors.
• If this is a monitor with BNC connectors and you are using them, make sure
  you had the video termination switches set correctly (75 ohms if this is
  the only monitor or the last monitor in a daisychain; HiZ if an intermediate
  monitor in a daisychain.) A very common cause of unbalanced or blooming
  colors assuming the monitor itself is good is incorrect settings of the
  termination.
• A bad connection, bad component, or short circuit in the video circuitry
  or CRT neck board could also result in strange colors.

Monitor manufacturing quality and cold solder joints

Any intermittent problems with monitors that cause random sudden changes in
the picture brightness, color, size, or position are often a result of
bad connections. Strategically placed bad connections can also cause parts to
blow. For example, a bad connection to the SCR anode in a phase controlled
power supply can result in all the current passing through the startup
resistor, blowing it as well as other components. I had a TV like this – the
real problem was a bad solder joint at a pin on the flyback. Thus, erratic
problems, especially where they are power or deflection related, should not be
ignored!

Bad solder joints are very common in monitors due both to poor quality
manufacturing as well as to deterioration of the solder bond after numerous
thermal cycles and components running at high temperature. Without knowing
anything about the circuitry, it is usually possible to cure these problems
by locating all bad solder connections and cleaning and reseating internal
connectors. The term ‘cold solder joint’ strictly refers to a solder
connection that was either not heated enough during manufacturing, was
cooled too quickly, or where part pins were moved before the solder had
a chance to solidify. A similar situation can develop over time with
thermal cycling where parts are not properly fastened and are essentially
being held in by the solder alone. Both situations are most common with
the pins of large components like transformers, power transistors and
power resistors, and large connectors. The pins of the components have
a large thermal mass and may not get hot enough during manufacturing. Also,
they are relatively massive and may flex the connection due to vibration
or thermal expansion and contraction.

These problems are particularly common with TVs and monitors – especially
cheaper monitors.

To locate cold solder joints, use a strong light and magnifier and examine
the pins of large components for hairline cracks in the solder around the
pin. Gently wiggle the component if possible (with the power off). Any
detectable movement at the joint indicates a problem. With the power on,
gently prod the circuit board and suspect components with an insulated
tool to see if the problem can be effected.

When in doubt, resolder any suspicious connections. Some monitors may
use double sided circuit boards which do not have plated through holes.
In these cases, solder both top and bottom to be sure that the connections
are solid. Use a large enough soldering iron to assure that your solder
connection is solid. Put a bit of new solder with flux on every connection
you touch up even if there was plenty of solder there before. However,
remove any obvious excess. Inspect for solder bridges, sliver, splashes,
etc. before applying power.

Why can’t monitor manufacturers learn to solder properly?

I can think of several potential reasons – all solvable but at higher
manufacturing cost.

1. Mass of large component leads (like shields) does not get adequately
   heated during manufacture leading to latent cold solder joints. While
   they may look ok, the solder never actually ‘wetted’ the heavy pins
   and therefore did not form a good mechanical or electrical bond.
2. Thermal cycles and differential thermal coefficients of circuit boards,
   traces, and solder. While it is not easy to do anything about the
   material properties, using plated through-holes or a similar mechanical
   via would greatly increase the surface area of the joint and prevent
   the formation of cracks.
3. Vibration. This is also directly related to the single sided circuit
   boards without plated through-holes to strengthen the joints.
4. Lack of adquate mechanical support (single sided circuit boards without
   plated through-holes (vias).

I believe that the single most significantimprovement would come about
by using plated trhough-holes but this would add to the cost and apparently
the consumer is not willing to pay more for better quality and reliability!
Some designs have used rivlets – mechanical vias instead of plated ones.
While this is good in principle, the execution has often been flawed where
cold solder joints resulted between the rivlets and the circuit board traces
due to lack of adequate process control.

Monitors, due to their generally higher cost compared to TV sets, should
be better constructed but not always.

Intermittent, flickering, or missing colors

This is a catch-all for some of the most common monitor problems. Most of
the causes boil down to bad connections of one form or another. However,
defective components like bias resistors on the CRT driver board or in the
video circuitry could also be at fault.

Note that due to the additive color scheme used in all emissive color displays
like CRT or flat panel TV sets and video monitors, a single missing primary
color (red, green, or blue) will result in the following appearance (for a
white screen):

    Missing Color       Appearance
  ------------------------------------------------
       Red              Cyan (blue-green)
       Green            Magenta (reddish-purple)
       Blue             Yellow

This may best be observed with a test pattern a color on-screen display
for which you recall the proper colors.

• Does whacking the monitor have any effect? If so, then bad connections
  are confirmed. If the color(s) come and go suddenly, then it is most likely
  *not* a CRT problem. The bad connections could be at the VGA cable, video
  driver board on the neck of the CRT, or elsewhere (see below).
• If the color fades in and out with a delay of about 10-15 seconds, it is
  probably intermittent power to the CRT filament for that color and probably
  means a bad CRT since the three filaments are wired in parallel inside the
  CRT. One of the internal connections has come loose.

  Look in the neck of the CRT to make sure all three filaments are glowing
  orange. If one is out or goes on and off, toss the monitor. Replacing the
  CRT is probably not worth it. However, if they all go on and off together
  (all colors would be fading in and out though perhaps not quite in unison),
  then bad connections for the CRT filaments on the CRT neck board are
  indicated.

Possible causes of intermittent or missing colors:

• VGA or other video input cable. Sometimes these develop intermittent
  problems at the connector to the VGA board. These may be internal
  to the cable in which case it will need to be replaced or if you are
  handy and have infinite patience, you can replace just the VGA connector.

  Alternatively, the male pins of the cable may not be making good contact
  with the female VGA socket. First try contact cleaner. If this does not
  work, gently squishing the male pins with a pair of needlenose pliers may
  provide temporary or permanent relief if the pins are a tad too small.
  However, if you go too far, you can damage or break the pins or cause the
  female socket to become enlarged and loose fitting for any other monitor
  you may use.

  If this just happened after reconfiguring your system and reconnecting
  the monitor or installing a new monitor, check your video connector – you
  may have bent over or pushed in pins 1, 2, or 3 – the R, G, and B video
  signals respectively.

  If you find a bent pin, ***carefully*** straighten it with a pair of
  needlenose pliers. If it is pushed in, try to grab onto it and pull it
  out – then put a drop of Epoxy or other adhesive at its base (don’t get
  any on the part of the pin that makes contact) to prevent it from being
  pushed in again.

  There may be cold solder joints on the VGA board itself at the VGA
  connector. These can be resoldered.

• Printed circuit board on the CRT neck. This is a common location for
  cold solder joints. Check with a bright light and magnifying glass
  for hairline cracks around the pins of larger parts. Prod and tap with
  an insulated tool to see if the problem is effected. Resolder if necessary.
• Cold solder joints elsewhere in monitor usually around the pins of
  large parts such as transformers, power transistors and resistors, and
  internal connectors. Inspect with a strong light and magnifier if
  necessary.
• Internal connectors that need to be cleaned and reseated. Remove,
  clean with contact cleaner, burnish, and replace.
• Bad filament connections inside the CRT (gradual fade in and out or
  one filament not lit). Replace CRT or monitor.

To narrow down the problem:

• Locate the output for the bad color on the video driver board on the
  neck of the CRT. This will probably read a significantly higher
  voltage than the corresponding pins for the good colors. A circuit
  problem is likely – probably on this board but it could be in other
  parts of the video circuitry.
• Test components on this board for the good and bad color channels. A
  shorted transistor or open resistor can kill one channel. Swap parts
  between good and bad colors to confirm.
• Gently pull the CRT neck board off of the CRT and replace it. This will
  tend to clean the contacts.
• Connect an output of the video circuit/chip that is working (i.e., a color
  that appears on the screen) to *all* three color drivers on the CRT neck
  board.

Some commentary on monitor and TV whacking

Anytime that intermittent symptoms are experienced, I recommend gently
whacking the patient to determine if mechanical shock or vibration affects
the behavior. Here are a couple of responses to this suggestion.

(From Marc Gelfond (71363.1700@CompuServe.COM).)

I just love the bit about “whacking it”. It brings to mind an
episode from the old Andy Griffith show, where a new fangled piece
of electronics gear, was broght into Emmets repair shop. After
many long hours of fruitless troubleshooting, out of frustration
Emmet gave the thing a whack, and sure enough it fixed the problem.

As we say in the Telephony business, it “CCWT” or Came Clear While Testing.
Another saying is that it “CCBFM” Came Clear By F—— Magic!!

(To which Gavin Adams (gaa@hopi.com) comments):

In the video industry we had a saying concerning malfunctioning gear:

“If it’s broke, hit it with a hammer”
“If that doesn’t fix it, paint it and sell it”

My DEC 16″ monitor is case in point. Evey once in a while it would
lose sync, and smacking it would bring it back (sometimes a few
smacks). Recently it gave up the ghost completely, and after the local
DEC office gave me a quote of $900 to fix it (Bermuda), I ordered a
new Viewsonic 17″ for the same price.

I ripped the guts out of the DEC beast, painted it with a marble finish,
put plants in it, and sold it! :>

Ghosts, shadows, or streaks in picture adjacent to vertical edges

Complaints about these kinds of problems are very common especially as
the screen resolution and necessary video bandwidth keeps increasing.
Most are due to cable and video termination deficiencies and not actual
monitor defects.

The video signals for red, green, and blue (or just a single signal for
monochrome) are sent over cables which are generally 75 ohm transmission
lines. These are coaxial cables that may be combined inside a single
sheath for VGA, SVGA, MACs, and many workstations but may be separate coaxes
with BNC (or other) connectors for other video applications.

Without going into transmission line theory, suffice it to say that
to obtain good quality video, the following conditions must be met:

• A good quality of cable must be used. This means one in which the
  characteristic impedance is close to the optimum 75 ohms, one which has
  low losses, and one which has good shielding. For installations
  using BNC connectors, a good quality of 100% shielded RG59U is often used.
  The BNC connectors must be properly installed or they will contribute
  to mismatch problems.
• Where multiple monitors are to be connected to a single video source,
  all wiring is done in a daisy chain fashion. The only taps permitted
  are the minimum necessary to connect each monitor to the chain. This
  usually means a BNC-T connector or a pair of connectors on the monitor
  for each video signal. T connections with cable must be avoided. (BNC
  cables only – SVGA monitors cannot be daisy chained without additional
  hardware.)
• Only the last monitor in the chain should be terminated in 75 ohms. All
  of the others must be set to Hi-Z. Monitors with BNC connectors will
  usually have one switch or a switch for each color to select termination.

Monitors for PCs, MACs, and many workstations usually have built in
termination and do not offer the choice of Hi-Z. This means that without
a video distribution amplifier, it is not possible to connect multiple
monitors of this type to a single video source with any expectation of a
good quality display.

Even adding a short extension cable or using an A-B monitor select box may
result in unacceptable image degradation especially at higher scan rates.

Failure to follow these rules will result in video ringing, ghosts, shadows,
and other unsightly blemishes in the picture. It is often not possible to
control all aspects of the video setup. The cable is often a part of the
monitor and cannot easily be substituted for a better one. The monitor
may not have properly designed circuitry such that it degrades the video
regardless of the cable and display board quality. The display card itself
may not have proper drivers or source termination.

Ironically, the better the video card, the more likely that there will
be visible problems due to termination. This is due to the very high
bandwidth and associated signal edge rates.

Some examples of common termination problems:

• Overly bright picture with trails following vertical edges, perhaps with
  periodic ringing. This is due to a missing termination. Check if the
  monitor is set for Hi-Z instead of 75 ohms. If there is no switch, then
  the termination may be faulty or the monitor may need an external resistor.
  For BNC connectors, plug-on terminations are available.
• Bright ghost images adjacent to vertical lines. This may indicate that
  the terminating resistor is greater than the impedance of the cable.
  You may be using Ethernet Thinnet cable by accident which is RG58 with
  an impedance of 50 ohms.
• Dark picture and ghost images adjacent to vertical lines. This may
  indicate that the terminating resistor is too low – multiple monitors on
  a chain all set for 75 ohms instead of just the last one. Or, an improper
  type of cable such as audio patch cord.
• Fuzzy vertical edges. This may indicate a poor quality cable or a run
  which is just too long. For high resolutions such as 1280×1024, the
  maximum cable length may be as short as 25 feet or less for poor quality
  cable. Better cable or fiber-optic repeaters may be necessary.
• Other similar problems – check cables for defective or improperly installed
  connectors. This is especially applicable to cables with BNC or UHF type
  connectors which require a kind of artistic talent to assembly properly and
  consistently. Throw out those extension cables and switch boxes!

If only 1 or 2 colors (of the R, G, and B) are effected, then look for
improper switch settings or bad connections (bad cable connectors are really
common) on the problem color cables.

General streaks or lines to the right of bright or dark areas

The problem is that on a white background the various objects leave a shadow
to their right. Not a duplicate image but more like horizontal dark streaks
on the white background. Also it seems that high intensity colors display
very bright but low intensity colors are overly dark (almost black). The
contrast and brightness adjustments may make no difference.

This could be a number of things but they are all in the video amplifier
and probably not the CRT driver board though this is possible. Dried
up filter capacitors could result in video dependent ripple on the power
supply lines. Bad coupling capacitors could result in similar symptoms
but probably for only one color, not all of them.

Since all colors are effected, look for something common like a bad power
supply. With a scope, this would probably be rather easy even without
schematics. If the brightness and contrast controls do nothing, this
would suggest some fault in their general area or the IC or transistors
they control in the video amps – and that this is not a CRT problem.
Locate the video amp IC if it uses one and locate a pinout – this should
be enough to determine which signals are faulty.

First, do check carefully for bad connections and other obvious failures.

This could also be a symptom of a bad CRT but this would be unusual
with a not-ancient monitor (and not if the brightness and contrast
controls have no effect).

Washed out picture

If you can obtain a full intensity raster by varying the brightness or screen
control, then your problem is most likely in the video amplifiers or power
for the video amplifiers.

If, however, the screen control varies the brightness but will not get
a bright raster, you probably have problems either with the HV power supply
or the filament supply for the CRT – is there the normal bright orange
glow at the base of the CRT? If it is dim or very reddish, there may
be a marginal connection or bad component in the filament circuitry.

Retrace lines in picture

During the time the electron beam is returning from right to left at the end
of a line and bottom to top (over the course of multiple lines), it is supposed
to be result in no visible light on the screen. However, a number of faults
can result in visible retrace lines.

The appearance will likely be a general reduction in contrast from the visible
horizontal retrace on every scan line and two dozen or so diagonal lines lines
(lower left to upper right) resulting from the vertical retrace.

The retrace lines may be either white or gray (possibly with a slight color
tint due to unequal settings of the color adjustments) or a primary color –
red, green, or blue. Anything in between is also possible but less likely.

White/gray retrace lines

Where all colors are involved – the lines are essentially white or gray (or
with a slight tint due to slight unequal settings of the color adjustments),
look for something common like an incorrectly adjusted screen (G2) or master
brightness/background/bias control or a problem in one of these circuits, a
defective power supply or a problem in the blanking circuitry:

• Screen (G2) or master brightness/background/bias control – mark setting and
  then see if a slight adjustment removes the retrace lines. See the chapter:
  “Monitor Adjustments”. Of course, if this happened suddenly, the problem is
  not due to a misadjusted control though a dirty pot is possible – turn it
  back and forth – this might clean it and restore normal operation.
• Power supply or connection to CRT neck board – insufficient voltage will
  result in the CRT never totally blanking. Check (usually scan derived)
  power supply components (from flyback).
• General power supply – check B+ for correct value and ripple. A main power
  supply fault might result in these symptoms (and usually many others).
• Blanking circuit – this may be a part of the video/chroma chip or separate.
  Check waveforms to determine if the blanking pulses are making it to the
  video output.

Red, green, or blue retrace lines

Where only one color is showing, suspect an incorrectly adjusted individual
background/bias control or bad part on the CRT neck board for that color.

• Individual brightness/background/bias control(s) – mark setting of pot for
  the problem color and then see if a slight adjustment removes the retrace
  lines. See the chapter: “Monitor Adjustments”. Of course, if this happened
  suddenly, the problem is not due to a misadjusted control though a dirty
  pot is possible – turn it back and forth – this might clean it and restore
  normal operation.
• Component or connection on CRT neck board – insufficient voltage to or
  incorrect biasing of the video driver for this color can result in the
  CRT never totally blanking. Compare voltages and signals, and swap
  components between good and bad channels to confirm.
• Blanking circuit – this may be a part of the video/chroma chip or separate.
  Check and compare waveforms of good and bad colors to determine if the
  blanking pulses are making it to the video output.

There is a slight possibility that a bad CRT may result in visible retrace
lines. To eliminate this possibility:

• Disconnect the filament – all evidence of a picture, raster, and retrace
  lines should disappear once the filaments/cathodes have cooled (15 seconds
  or so. If there are still visible retrace lines, the CRT is suffering
  from cold or field emission from someplace (may not even be the cathode).
• Turn down the screen (G2) control on the flyback (usually). If one color
  remains no matter how you set the control, again there is some kind of
  weird emission from the CRT. However, if white/gray retrace lines remain,
  the problem may be in the screen supply.

See the section: Bad CRT causing retrace lines.

Bad CRT causing retrace lines

(From: Jeroen H. Stessen (Jeroen.Stessen@philips.com).)

The TV which I bought last started developing retrace lines after a month or
so of use. I took it back to the lab for warranty (special deal) and had it
examined by the real experts. They found that even with the filament supply
disconnected and VG2 at 0V the screen would still light up. They could even
see that the electrons weren’t even coming from the cathode. That was with
only the picture tube in a test rig. So in this case the obvious conclusion
had to be that the tube was bad, and it was replaced (32″ 16:9 SF, very $$).
It had something to do with processing problems during manufacturing of the
electron guns.

So even if this was a rare case, it *can* happen that retrace lines are due
to a bad picture tube. It’s more usual to suspect the VG2 (screen voltage)
or a defect somewhere in the RGB video path.

Red, green, or blue full on – fog over picture

This could be a heater-cathode (H-K) short in the CRT, a failure of a
component in the chroma circuits or video output (driver board), or bad
connections there or elsewhere.

Don’t panic – heater-cathode shorts in CRTs can often be worked around.

Note: before proceeding, it is a good idea to make sure that the screen is
degaussed – else you could be attempting to track down problems with the wrong
color!

Some simple tests can confirm or rule out other possibilities.

• Compare the voltages for the video drive signals to the CRT on the little
  board on the neck of the CRT with the CRT both connected and unplugged.
  A schematic will help greatly in locating these signals.
  • If there is a significant difference especially on the bad color, then the
    CRT is a likely candidate. Try tapping the neck of the CRT GENTLY (with
    it plugged in and while viewing a picture) to see if it is an intermittent
    problem.
  • If there is no significant difference, you may have a bad driver or a
    problem in the chroma circuits.
• Look for bad connection/cold solder joints, probably on the little
  board on the neck of the CRT. Use an insulated stick to gently prod
  the board and its components in an effort to induce/cure the problem.
  Look carefully for hairline cracks around the component leads.
• You can swap components between two colors and/or test with an ohmmeter
  on that driver board to determine what is bad. The nice thing about
  color monitors and TVs is that there three copies of each of these
  components. Swapping and/or comparisons between these is an excellent
  diagnostic technique.
• Another simple test: Disconnect the cathode for the full-on color from its
  drive. If it is still full-on, there is probably an H-K short in the CRT
  since the only way to get each color on the screen is via the cathode
  connection to the CRT neck board. If it is removed and there is still that
  color, the current must be taking another path inside the CRT.
• Alternatively, interchange the outputs of the bad color with a good one
  by jumpering on the video driver board (on the CRT neck). If the bad
  color changes, then the problem is in the circuitry and not the CRT.

  Here is the procedure in more detail (example for red full on):

  (From: J. K. Emerine (jkemerine@aol.com).)

  To identify if the fault is in the crt or a control problem try this (WITH
  SET OFF):

  On the CRT board, lift the output end of the green cathode final resistor.
  Do the same with the offending red cathode’s resistor. Use short insulated
  jumpers to ‘swap’ drive signals – drive the red cathode with the green
  drive and the green cathode with red drive. (Note that if this problem
  only occurs after a warmup period, color at turn on will be – well – wierd,
  but it is just a test.)

  • If the symptom returns=”goes red” the CRT is shorting. (See the
    section: Providing isolation for a CRT H-K short.
    — Sam.)
  • If instead the symptom becomes ‘goes green’ then the red drive leg has
    the fault and the CRT is probably good. (In this case, there may be bad
    connections or a bad component on the CRT drive board or further back
    in the chroma circuitry. — sam)

Totally white screen (probably with retrace lines)

There may or may not be any indication of a picture. This may be a problem in
the high voltage power supply (SCREEN, G2), loss of power or a fault in the
video output drivers, other video amp problems, or a bad (shorted) CRT.

Is focus still reasonably sharp? If not, try adjusting it (usually on the
flyback or a separate little panel). If changing focus affects brightness
significantly, there is a short between the two supplies – either in the
HV power supply or CRT. See the section: Bad focus
and adjustment changes brightness. In this case, changing SCREEN (G2,
also on the flyback) may also affect focus or may not do anything.

Try adjusting SCREEN. If it has no affect, a problem in its power supply
from the flyback is possible. If you have a high impedance voltmeter (not
just a DMM, the resistance of the voltage divider supplying SCREEN is hundreds
of M ohms), check it while changing the SCREEN control. If it does not change,
you have found a definite problem.

Assuming that adjusting FOCUS and SCREEN result in normal behavior and do
not strongly interact, the problem is likely in the video circuitry or output
drivers.

Check the power to the CRT video output drivers on the little board on the
neck of the CRT. If this failed, all three video outputs will be full on.
If you have a scope, look at the video outputs – they should be varying
between over 100 V and a low value. If they are missing or very low all
the time, there is a problem further back in the video chain.

See the other sections relating to brightness and high voltage problems
as well.

Shorts in a CRT

Occasionally, small conductive flakes or whiskers present since the day of
manufacture manage to make their way into a location where they short out
adjacent elements in the CRT electron guns. Symptoms may be intermittent or
only show up when the TV or monitor is cold or warm or in-between. Some
possible locations are listed below:

• Heater to cathode (H-K). The cathode for the affected gun will be pulled
  to the heater (filament) bias voltage – most often 0 V (signal ground). In
  this case, one color will be full on with retrace lines. Where the heater
  is biased at some other voltage, other symptoms are possible like reduced
  brightness and/or contrast for that color. This is probably the most
  common location for a short to occur.
• Cathode to control grid (K-G1). Since the G1 electrodes for all the guns
  are connected together, this will affect not only the color of the guilty
  cathode but the others as well. The result may be a very bright overloaded
  *negative* picture with little, none, or messed up colors.
• Control grid to screen (G1-G2). Depending on circuitry can result in any
  degree of washed out or dark picture.
• Screen to focus (G2-F). Screen (G2) and focus voltage will be the same and
  the controls on the flyback will interact. Result will be a fuzzy white
  raster with retrace lines and little or very low contrast picture. Symptoms
  will be similar to those of a flyback with breakdown in the focus/screen
  divider network.
• Focus to high voltage (F-HV). High voltage will be pulled down – probably
  arcing at the focus spark gaps/other protective devices. Line fuse and/or
  HOT may blow. A high impedance short may only result in increased focus
  voltage but this is probably unusual.
• Other locations between electron gun elements as feed wires.

Except for the high voltage to other places, the short may actually be located
in the CRT *socket* or even on the CRT neck board, probably in the spark
gap(s) for the problem pins. Remove the socket and test between the suspect
pins on the CRT itself. If the CRT itself is fine, the spark gaps should be
inspected and cleaned/repaired and/or components replaced. At this point, the
cause may still be present – a short inside the flyback for example resulting
in excessive voltage on one or more pins.

Assuming this is not the case, replacing the CRT may be the best solution
but there are a variety of ‘techniques’ that can often be used to salvage a
monitor that would otherwise end up in the dump since replacing a CRT is
rarely cost effective:

1. Isolation – this will usually work for H-K shorts as long as only one gun
   is involved. However, with high video bandwidth monitors, there may be
   some smearing of the affected color due to the added capacitance of the
   transformer and filaments now connected to its video signal.
2. Blowing out the short with a capacitor – depending on what is causing the
   short, this may be successful but will require some experimentation.
3. Placing the CRT (TV or monitor) face down on a soft blanket and *gently*
   tapping the neck to dislodge the contamination. Depending on the location
   of the short, one side or the other might be better as well. Sometimes,
   this can be done in-place while watching the picture.

A combination of (2) and (3) may be required for intermittent shorts which
don’t appear until under power. See the sections below for additional
details. However, for shorts involving the focus and high voltage elements,
even a sharp edge can result in arcing even if there is no actual short.
There is no remedy for these types of faults.

Providing isolation for a CRT H-K short

This procedure will substitute a winding of your own for the one that is
built in to the flyback to isolate the shorted filament from the ground
or voltage reference. Note that if you have a schematic and can determine
where to disconnect the ground or voltage reference connection to the
filament winding, try that instead.

The flyback is the thing with the fat red wire coming out of it (and perhaps
a couple of others going to the CRT board or it is near this component
if your set has a separate tripler) and may have a couple of controls for
focus and screen. It should have some exposed parts with a ferrite core
about 1/2-3/4″ diameter.

The filament of the CRT is the internal heater for each gun – it is what
glows orange when the set is on. What has happened is that a part of the
fine wire of the bad color’s filament (assuming this is indeed your problem)
has shorted to the cathode – the part that actually emits the electrons.
Normally, the heater circuit is grounded or tied to a reference voltage
so when it shorts to the cathode, the cathode voltage level is pulled to
ground or this reference.

You will need some well insulated wire, fairly thick (say #18-22). Find a
spot on the flyback where you can stick this around the core. Wrap two
turns around the core and solder to the CRT filament pins after cutting the
connections to the original filament source (scribe the traces on the board
to break them). Make sure you do not accidentally disconnect anything else.

This winding should cause the filaments to glow at about the same brightness as
before but now isolated from ground. If they are too dim, put another turn
on the flyback to boost the voltage as low filament temperature will result in
reduced emission, blooming, and possible damage to the cathodes after awhile.
(Don’t go overboard as you may blow the filament totally if you put too many
turns on the core – you then toss the monitor.)

Route the wires so that there is no chance of them getting near the high
voltage or any sharp metal edges etc. Your picture quality may be a tad
lower than it was before because of the added stray capacitance of the
filament wiring being attached to the the (formerly bad) video signal, but
hey, something is better than nothing.

Rescuing a shorted CRT

If the short is filament-cathode (H-K), you don’t want to use the following
approach since you may blow out the filament in the process. If this is the
case, you may be able to float the filament and live with the short (see the
section on: “Red, green, or blue full on – fog over picture”.

Shorts in the CRT that are between directly accessible electrodes can
be dealt with in a more direct way than for H-K shorts. At this point
you have nothing to loose. A shorted CRT is not terribly useful.

If the short is between two directly accessible electrodes like cathode-grid,
then as a last resort, you might try zapping it with a charged capacitor.

Unplug the CRT socket!

Start with a relatively small capacitor – say a few uF at a couple hundred
volts. Check to see if the short is blown after each zap – few may be needed.
Increase the capacitance if you feel lucky but have had little success with
the small capacitor.

If the fault is intermittent, you will, of course, need to catch the CRT
with the socket disconnected and the short still present. Try some gentle
tapping if necessary. If you do this with the charged capacitor across
the suspect electrode, you **will** know when the short occurs!

Also see the section: High voltage to focus short.

High voltage to focus short

Symptoms would be (with the unit powered and high voltage present):

• With the CRT neck board plugged into the CRT, the focus spark gap is likely
  arcing.
• With the socket unplugged, putting anything connected to ground (or any
  other circuitry) near the focus pin would result in a juicy spark or arc.
  WARNING: Removing the CRT socket and powering the unit may destroy the CRT
  on some models. See the section: Warning about
  disconnecting CRT neck board.

If the CRT is gassy or up to air, forget it – it might make a decent fish
tank :-). In this case, there would be visible arcing INSIDE the CRT probably
not confined to a single location.

However, if there is just a metal whisker between the F and HV, that might
be able to be cleared by careful tapping or a charged capacitor. You may even
be able to see it if you were to remove the yoke – the gap is pretty large,
about 1-2 mm – the last gap between electrodes before the start of the
internal (Dag) coating.

See the section: Rescuing a shorted CRT.

Note that other damage may have been done as

Other components including the flyback, HOT, and parts on the CRT neck board
and beyond, may have been damaged as a result of the short. Zapping the CRT
may be just the beginning of what is required to repair it all.

Dark picture

A monitor with a picture that is too dark may have a fault or the CRT may
just be near the end of its useful life.

First, confirm that your video source – computer, camera, etc. – is producing
a proper signal.

Is the brightness at all erratic? Does whacking the monitor have any effect?
If so, then you may have bad connections on the CRT driver card or elsewhere.
If the brightness tends to fade in and out over a 10 to 20 second period,
a bad filament connection is likely. Check for the normal orange glow of
the filaments in the neck of the CRT. There should be 3 orange glows. If
they are excessively reddish, very dim, or fade in and out, you have located
a problem. See the section: Picture fades in and out.

Common causes of brightness problems:

1. Dirty CRT faceplate or safety glass. Don’t laugh. It sounds obvious, but
   have you tried cleaning the screen with suitable screen cleaner? It is
   amazing how dirty screens can get after a few years – especially around
   smokers!

   (From: A. R. Duell (ard12@eng.cam.ac.uk).)

   “I once spent a morning battling with a DEC VT105 terminal with a very
   dim and washed out picture, and only after checking everything on the
   video board did I wipe over the screen. That cured it. It’s amazing
   how dirty screens can get after a few years use.”

   Wipe gently with a slightly dampened cloth – not soaking or you may end
   up with real problems when the water drips down inside and hits the
   electronics!

2. Old CRT. The brightness of the CRT deteriorates with filament on-time.
   It doesn’t matter much what you are doing or if you use a screen saver.

   An indication of a weak CRT would be that turning up the SCREEN (G2) or
   master brightness control only results in a not terribly bright gray raster
   before the retrace lines show up. There may be indications of poor focus
   and silvery highlights as well. A CRT brightener may help. See the
   sections: Brightening a old CRT and
   Monitor life, energy conservation, and laziness.

3. Bad component in filament circuit or bad connection reducing filament
   voltage. This should be easy to check – there are only a few parts
   involved. If it is erratic, bad connections are likely.
4. Brightness control faulty – bad pot, bad connections, or problem with its
   power supply. Depending on specific problem, control may or may not have
   any effect. If digitally adjusted, there could be a problem with the
   logic or control chip. If the button or menu item has no effect at all,
   then a logic or control problem is likely.
5. Improperly set SCREEN (G2) voltage (usually on flyback) or faulty divider
   network. See the section: Brightness and color balance
   adjustment.
6. Improperly set video bias (background) levels or fault in video drive
   circuitry. See the sections starting with: “Optimal procedure for setting
   brightness/background and screen adjustments”.
7. Fault in video amplifiers. With all three color affected equally, this
   would most likely be a power supply problem. A video amplifier problem
   is likely if turning up the SCREEN (G2) or master brightness control
   results in a very bright raster before the retrace lines appear. Cheack
   signals out of the video/chroma IC.
8. Fault in beam or brightness limiter. Many TVs and monitors measure the
   beam current (possibly indirectly) and limit the maximum to a safe value.
   The purpose of this may be to protect the CRT phosphors, and/or to assure
   that the power supply does not go out of regulation, and/or to limit X-ray
   emission. If this circuit screws up, a dark picture may result. Checking
   the signals and voltages at the CRT socket should determine if this is the
   problem.
9. High voltage is low. However, this would likely result in other symptoms
   as well with focus, size, and geometry.

Brightening an old CRT

If performing adjustments of the internal background and/or screen
controls still results in a dark picture even after a long warmup period
(and the controls are having an effect – they are not faulty), the CRT may
simply be near the end of its useful life. In the old days of TVs with
short lived CRTs, the CRT brightener was a common item (sold in every
corner drugstore, it seemed!).

First confirm that the filaments are running at the correct voltage – there
could be a marginal connection or bad resistor or capacitor in the filament
power supply. Since this is usually derived from the flyback, it may not
be possible to measure the (pulsed high frequency) voltage with a DMM but
a service manual will probably have a waveform or other test. A visual
examination is not a bad way to determine if the filaments are hot enough.
They should be a fairly bright orange to yellow color. A dim red or almost
dark filament is probably not getting its quota of electrons. It is not be
the CRT since all three filaments are wired in parallel and for all three to
be defective is very unlikely.

If possible, confirm that the video output levels are correct. For cathode
driven CRTs, too high a bias voltage will result in a darker than normal
picture.

CRT brighteners are available from parts suppliers like MCM Electronics.
Some of these are designed as isolation transformers as well to deal with
heater-to-cathode shorts.

You can try a making a brightener. Caution: this may shorten the life of
the CRT – possibly quite dramatically (like it will blow in a couple of
seconds or minutes). However, if the monitor or TV is otherwise destined
for the scrap heap, it is worth a try.

The approach is simple: you are going to increase the voltage to the
filaments of the electron guns making them run hotter. Hopefully, just
hotter enough to increase the brightness without blowing them out.

Voltage for the CRT filament is usually obtained from a couple of turns
on the flyback transformer. Adding an extra turn will increase the voltage
and thus the current making the filaments run hotter. This will also
shorten the CRT life – perhaps rather drastically. However, if the monitor
was headed for the dumpster anyhow, you have nothing to lose. You can just
add a turn to an existing winding or make your own separate filament winding
as outlined in the section: Providing isolation for a
CRT H-K short.

In some monitors, there is a separate filament supply on the mainboard – this
should be obvious once you trace the filament wires from the video driver
board). In this case, it still may be possible to increase this output or
substitute another supply but a schematic will be required.

There are also commercial CRT rejuvenators that supposedly zap the
cathodes of the electron guns. A TV or monitor service center may be
able to provide this service, though it is, at best, a short term fix.

Color balance changes across screen from left to right

The characteristics are that a solid white screen will tend to be blue tinted
on one side and red tinted on the other. This is usually a subtle effect and
may be unavoidable with some designs.

There are several possibilities:

1. Purity – this means the beams are landing on the wrong phosphor dots.
   This is what would be affected by moving from one location to another
   or even rotating the TV on its base without degaussing. If the problem
   just appeared, degaussing may be needed.

   What do you have near the TV or monitor? Loudspeakers or other devices
   which generate magnetic fields can easily cause all sorts of color purity
   problems. Relocate the offending device(s) or the TV or monitor and then
   degauss it.

   See the section: Degaussing (demagnetizing) a CRT.

   If the problem still persists, purity adjustment may be needed. However,
   this isn’t likely to have changed so look for other causes before tackling
   these adjustments.

2. Unequal electron gun to shadowmask/screen distance – the electron beams for
   the red and blue video travel slightly different distances on the left and
   right sides of the screen so their intensity (due to focus not being optimal
   and other factors) in each case may differ slightly affecting color balance.
3. Doming – This would only happen in very bright areas and causes the
   shadow mask to expand and distort. (Doming should not be a problem with
   Trinitron CRTs which use tensioned wires in their aperture grill.) This
   would also not really affect left-right color balance in particular.

I don’t really know how much of a problem (2) is in practice or whether some
manufacturers compensate for it.

Bleeding highlights

On very bright areas of the picture, one or more colors may bleed to
the right resulting in a trail of those colors. The difference between
this problem and the section: Trailing lines in one
or more colors is that in this case, only highlights are affected.

One cause of this is that the color gain, contrast, or intensity controls
(whatever they are called on your monitor) are set too high. See the section
on: “Brightness and color balance adjustment”. Check the settings of any
brightness limiter controls as well.

Trailing lines in one or more colors

Assuming this is not a form of ghosting resulting from cabling and/or use
of switchboxes, etc, then it could be any of the following:

• Poor decoupling in the power supplies for the video drive circuits –
  probably on the CRT neck board. Check for bad (low uF or high ESR) filter
  capacitors (electrolytic mostly) on this board or the power supplies
  feeding it.
• Insufficient CRT filament voltage. This could be a result of bad
  connections or a bad component in the filament power supply (probably from
  the flyback). Check to see if the filaments are glowing bright orange and
  check the voltage if possible (though this can be tricky since it is often
  fed from a winding on the flyback and is a pulse waveform, not DC or a
  sinusoid. The service manual will probably have info and waveforms.
• Bad CRT (more likely if only one color is affected). A weak electron gun
  can result in this behavior. Swap it with one that work properly. If the
  same color is still bad, that CRT gun is weak. The CRT will need
  rejuvenation or need to be replaced (more likely, the entire monitor will
  be tossed into the dumpster).

Purity problems with bright pictures

Setting the brightness excessively high may result in enough heating
of the shadow mask to distort it. IF severe enough, the positions of the
holes will shift enough to result in visible purity problems. This is
less of a problem with tubes using an InVar shadow/slot mask. It should
also be less of a problem for Trinitron aperture grille CRTs.

The only solution is to reduce the brightness.

Why does the intensity appear so non-uniform in bright areas?

Actually, the intensity variation is likely to be even worse than you might
think – possibly as much as 2:1 from the center to the corners. In most cases
you do not notice it. With large deflection angle tubes, fewer electrons make
it to phosphor dots near the edge of the screen. It is simple geometry.

(From: Bob Myers (myers@fc.hp.com).)

It is extremely difficult for any CRT display to maintain perfect brightness
and color uniformity across the entire image. Just the geometry of the
thing – the change distance from the gun to the screen as the beam is scanned,
the changing spot size and shape, etc. – makes this nearly impossible, and
there can also be variations in the phosphor screen, the thickness of the
faceplate, etc.. Typical brightness-uniformity specs are that the brightness
won’t drop to less than 70% or so of the center value (usually the brightest
spot on the screen).

On color tubes, the lack of perfect brightness uniformity is aggravated
by the lack of perfect COLOR uniformity and purity. What appear to be
“dark spots” on a solid gray image may actually be beam mislanding (color
purity) problems, which may to some degree be remedied by degaussing
the monitor.

Again, *some* variation is normal; if you think you’re seeing too much, you
can try degaussing the thing and seeing if that helps. If it doesn’t,
then the question is whether or not the product meets its published specs,
and that ‘s something you’ll have to discuss with the manufacturer or
distributor.

Brightness changes from left-to-right across screen

Slight variations in brightness across the face of the CRT are not unusual.
In fact, if you used a photometer to actually measure the brightness, you
might be amazed at the actual variance even with the best monitor or TV – you
just don’t notice it. However, a major variation – usually a decay from left
to right but could be the other way indicate a component failure. Of course,
make sure the face of the screen is clean!

• A fault in the power supplies to the video amplifier and/or video output
  circuits. Most likely, an electrolytic capacitor has dried up and is not
  adequately filtering the power derived from the flyback which then has
  ripple at the horizontal scan rate and thus locked to the screen. The
  voltage decays from left-to-right between horizontal flyback pulses.

  The most likely location for these capacitors is in the vicinity of the
  flyback transformer on the mainboard or on the CRT neck board. Check the
  capacitors with capacitor tester or ESR meter and/or take a look at the
  power right at the video amplifier and video output drivers.

• Horizontal linearity is bad – this may actually be a horizontal geometry
  problem and not a brightness problem.

  See if objects on left side of the screen are stretched compared to those on
  the right (or vice-versa). If they are, the problem is in the horizontal
  deflection circuits – possibly a bad (or in the case of a multiscan monitor,
  correctly selected) S correction capacitor or linearity coil.

• Inoperative degauss circuit, monitor moved or rotated without degaussing,
  or magnetic field from some other device (like a permanent magnet) is
  affecting CRT – slight amounts of magnetization may reduce brightness (by
  moving the beams into the black space between phosphor dots) before affecting
  color purity (where the beams land on the wrong phosphor dots).

  See if the degauss button, if present, does anything. Try deguassing
  manually. See the section: Degaussing (demagnetizing)
  a CRT.

Picture fades in and out

If the picture faded away on the order of 10-20 seconds (and if it comes
back, also comes up to full brightness in same time frame – possibly
with the persuasion of some careful whacking) AND with NO other
significant changes such as size, focus, etc., then take a look in the back of
the tube for the filaments to be lit – the orange glow near the CRT socket. If
the glow is coming and going as well, then you probably have a bad solder
connection on the circuit board on the neck of the CRT. Look for fine cracks
around pins on that board. Try prodding it with an insulating stick to see if
the picture comes back. Resolder if necessary. It is probably not a bad CRT
as the filaments are usually wired in parallel and all would not go bad at the
same time.

However, if only a single color fades in and out, then a bad connection
inside the CRT is a distinct possibility – look for only one of the
filament’s glow to be coming and going. This is probably not worth fixing
since it will require CRT replacement.

If the picture faded away with other symptoms, then there is probably
a fault in the video amplifier/output one of its power supplies –
still probably a loose connection if you are able to get it back by
whacking.

Occasional brightness flashes

These may last only a fraction of a scan line or much much longer.

Make sure it is not the video source – try another one.

This could mean an intermittent fault in a variety of places including
the video circuitry and SCREEN power supply:

• Brightness circuitry – SCREEN, master background or its power supply.
  Could be in or around flyback or focus/screen divider. Could perhaps
  be in the CRT, but probably less likely.
• Video amp before or at chroma demodulator (if composite input) – since
  after this point, you would most likely get colored flashes since only
  one of the RGB signals would likely be effected. However, a bad power
  connection to the video circuitry could cause all the colors to be
  affected.

If you still get flashes, it should be quite easy to monitor either
the video outputs or SCREEN supply (with a HV divider on your scope) for
noise. Then trace back to power or noise source.

Occasional static, lines, spots, or other unsightly blemishes

First, confirm that these are not video source – PC – related. Try the
monitor on another computer. This may be a problem with the hardware or
driver (software) for the video card, the O/S, or memory or bus speed.

If it is not computer related, then it could be arcing, corona, bad
connections, or some electronic component breaking down. See the
appropriate sections for these problems.

Note that problems in absolutely fixed locations or with an extent related
to pixel sizes in the video card are nearly always computer/video card
related and not due to a faulty monitor.

Flickering monitor

First, make sure your scan rate is set high enough (but not beyond the
capabilities of the monitor). A scan rate less than 60 Hz is likely to
result in annoying flicker especially at high brightness levels.

See if the flickering correlates with any processor or disk activity indicating
a software driver or video card problem.

Assuming neither of these applies and you are not doing your work by
candlelight, a flickering image is probably due to an intermittent arc
or short, probably in the high voltage section near or at the flyback
transformer. However, it is also possible that it is due to a simple
bad connection elsewhere.

So the first thing to do will be to remove the cover and without touching
anything, carefully examine for any obvious signs of bad connections, arcing,
or burned areas. In particular look for:

• hairline cracks around the pins of large components like power transistors,
  power resistors, transformers, and connectors.
• any discoloration, cracking, other unusual signs on the flyback. The
  flyback also provides, via a high resistance divider network, the several
  kV for focus and several hundred V for the G2 (screen) CRT electrode. These
  are the voltages that may be intermittently changing and resulting in flicker.

Now, with the monitor powered in a darkened room with a normal picture
(use the highest resolution at which your monitor will work as this should
put the most stress on it, maybe).

• Look for any arcing or corona around the area of the flyback or the neck
  of the CRT first, then just anywhere.
• Use a well insulated stick (wood or plastic) to gently prod the circuits
  board, components, wires, etc. to see if you can induce the problem.

There will probably be a pair of adjustments on the flyback itself. One of
these is FOCUS and the other is SCREEN – essentially a master brightness.

• Now, with one hand in your back pocket, try turning each of these a
  fraction of a turn in each direction. Don’t worry, you cannot hurt anything
  by doing this. The FOCUS should only change the sharpness of the picture.
  The SCREEN should only change the brightness. In both cases, this should
  be a smooth effect. Sometimes, these controls will simply get dirty and
  cause the problems you have seen. In this case, just moving them back
  and forth may clean them. If one affects the other – if turning focus
  alters brightness or vice-versa, there is a short between the focus and
  screen voltages, probably inside the flyback but it could be elsewhere.

It is likely that all of the above tests will come out negative as
you may have an intermittent short internal to the flyback which can only
be fixed by replacement. However, eliminate the easy fixes first.

Excessive brightness and/or washed out picture

There are a number of possibilities including incorrect screen (G2) or bias
(G1) voltages, or a problem in the video or blanking circuitry. Any of these
could be the result of bad connections as well. A short in the CRT can also
result in these symptoms.

• Excessive brightness/washed out picture is often an indication of a
  problem with the screen (G2) supply to the CRT. May be a bad capacitor
  or resistor divider often in the flyback transformer assembly or on
  the board on the neck of the CRT.
• If the excessive brightness just developed over time, then a simple
  adjustment of the screen or background brightness controls may keep
  it (and you) happy for a long time.

  When good, a typical value would be in the 200 to 600 VDC at the CRT. The
  screen (it may also be called master brightness, bias, or background) control
  should vary this voltage. However, it may be difficult to measure as the
  resistors in the voltage divider network may be quite large – hundreds of M
  ohms. If your unit has an external screen control (less likely these days)
  and it has no effect, trace out the circuitry in the immediate vicinity and
  check the resistors and potentiometer for opens, look for bad connections,
  etc. If it is built into the flyback transformer and is sealed, the entire
  flyback will need to be replaced unless the actual problem turns out to be a
  bad connection or bad component external to the flyback.

• Where the brightness control has no effect, suspect a missing bias supply
  to the G1 (control grid) electrodes of the CRT. This is usually derived from
  the flyback with a simple rectifier/filter capacitor power supply. Parts
  may have failed (though not likely the flyback itself). Adjusting the user
  brightness control should vary this voltage over a typical range of 0 to -50
  V with respect to signal ground.
• It could also be a problem with biasing of the video output transistors.
  There may individual controls for background brightness on the little board
  on the neck of the CRT. However, we are looking for a common problem since
  all colors are wrong in the same way. This is likely to be a missing voltage
  from a secondary supply from the flyback.
• A short between electrodes inside the CRT can result in brightness
  problems. It may be possible to check this with an ohmmeter with the power
  off and the CRT socket removed. Test between G1, G2, and F where all colors
  are affected though a short between F and G2 will result in the focus control
  changing brightness and vice-versa – a classic symptom.

  However, in some cases, it only shows up when operating and one must deduce
  the presense and location of the short from its affect on voltages and bias
  levels.

  See the section: Rescuing a shorted CRT and other
  related topics.

First, check for bad connections/cold solder joints by gently prodding
with an insulating stick. Check voltages and bias levels.

Focus problems

Slight deterioration in focus can be corrected by adjusting the focus
control usually located on the flyback transformer. Sometimes, this
is accessible externally but usually not. On monochrome monitors, the
focus control, if any, may be located on the main board.

Don’t expect to have perfect focus everywhere on the screen. Usually there
will be some degradation in the corners. A compromise can generally be
struck between perfect focus in the center and acceptable focus in the
corners.

If the adjustments have no effect, then there is probably a fault in the
focus power supply.

For most color TVs and monitors, the correct focus voltage will be in the
4 to 8 kVDC range so you will need a meter that can go that high or some big
resistors to extend its range or a HV probe. You must use a high impedance
meter as the current availability from the focus power supply is very low.

The pots in the flyback are sometimes accessible by removing their cover,
which may snap on. However, a typical focus circuit will have a large
value resistor potted inside the flyback (like 200 Megohms).

Try to measure the focus in-circuit. If the value you read is very low
(assuming your meter has a high enough impedance not to load the circuit
appreciably), then disconnect the wire (from the PCB on the neck of the
CRT or wherever) and measure again and observe any change in picture.

• If still low, then almost certainly there is a problem with the pot or
  the flyback. See if you can open it enough to measure and/or disconnect
  the pot. If the problem is inside the potted part of the flyback, the
  only alternative is a new flyback or an external divider if you are so
  inclined. However, once the focus network goes bad inside the flyback,
  there is an increased chance other parts will fail at some point in the
  future.
• If the voltages check out with the CRT disconnected, there is a chance of a
  bad CRT or of a shorted component on the PCB on the neck of the CRT. Look
  for shorted capacitors or burnt or damaged traces.

  Measure the voltage on the focus pin of the CRT. WARNING: If there is an
  internal short, you could have the full 25kV+ at this location! If you get
  a reading, this would be an indication of an internal short in the CRT. See
  the section “Shorts in a CRT”.

Bad focus (fuzzy picture)

Focus voltage on the CRT is usually in the range of 2-8 kV DC and should
be controllable over a fairly wide range by the focus pot – usually located
on the flyback or a little panel in its vicinity:

• If adjusting the pot results in a position of acceptable focus, you may be
  done. It is not unusual for the focus setting to drift a over time.
• If the setting is already as good as possible but not really good enough,
  the CRT may be tired. Alternatively, the filament voltage may be too low.
  Check for bad connections in the filament circuit.
• If the optimal setting is out of range of the focus pot, the problem is
  likely leakage in the focus divider in the flyback or one of the components
  on the CRT neck board.

Also see the sections: Focus adjustment and
Focus drifts with warmup.

The focus wire usually comes from the flyback or if the general area or from a
terminal on a voltage multiplier module in some cases. It is usually a wire
by itself going to the little board on the neck of the CRT.

If a sparkgap (a little 2 terminal device with a 1/8″ gap in the middle)
is arcing with power on, then the resistive divider has shorted inside
the flyback, focus board, or HV multiplier – whatever you TV has – and
the this unit will need to be replaced. Ditto if the SCREEN control affects
focus and/or vice-versa.

Using a suitable high voltage meter (range at least 10 kVDC, 1000 M ohm or
greater input impedance), you should be able to measure it connected and
disconnected. The ground return will be the outside coating of the CRT which
may or may not be the same as the metal chassis parts. If the voltage is very
low (less than 2 kV) and the pot has little effect:

• When measured right off of the source disconnected from the CRT neck board,
  then the problem is probably in the focus network in the flyback (or wherever
  it originates). Sometimes these can be disassembled and cleaned or repaired
  but usually requires replacement of the entire flyback or voltage multiplier.
  Note: you may need to add a HV (10 kV) capacitor between the focus wire and
  DAG ground to provide filtering so you get a DC level for your meter.
• When measured with the focus wire attached to the CRT neck board with the
  CRT connected but reasonable with the CRT unplugged, there is probably a
  short between the focus and another electrode inside the CRT. See the
  section: Rescuing a shorted CRT.
• When measured with the focus wire attached to the CRT neck board with the
  CRT unplugged, there is likely a component on the CRT neck board that is
  leaky or breaking down. Also, check for decayed (tan or brown) glue which
  may turn leaky with age.

Focus drift with warmup

This could be due to a problem with the focus voltage power supply, components
on the CRT neck board, or a tired worn CRT.

Focus is controlled by a voltage of 2-8 kV DC usually derived from the flyback
transformer and includes some resistors and capacitors. One of these could
be changing value as it warms up. (assuming nothing else changes significantly
as the unit warms up – e.g., the brightness does not decrease.)

Focus voltage is derived from a subset of the high voltage winding on the
flyback using a resistive voltage divider which includes the focus pot.
These are extremely high value resistors – 200 M ohm is common – and so
leakage of any kind can reduce or increase the focus voltage. All other
things being OK – i.e., the picture is otherwise fine – I would suspect this
type of failure rather than the CRT.

The connection to the CRT is usually a separate wire running from the flyback
or its neighborhood to the CRT neck board. Look for components in this
general area. Use cold spray or a heat gun to isolate the one that is
drifting. If you have access to a high voltage meter, you should be able
to see the voltage change as the TV or monitor warms up – and when you cool
the faulty part. If it is in the flyback, then sometimes the part with the
adjustments clips off and can be repaired or cleaned. Most often, you will
need to replace the flyback as a unit.

• If the optimal adjustment point of the focus control doesn’t change that
  much but the best focus is simply not as good as it should be, the CRT is
  probably the problem. However, if the optimal point produces acceptable
  focus but it changes (and possibly moves off of one end of the adjustment
  knob range) as the unit warms up, the flyback or one of the components on
  the CRT neck board are likely drifting.
• If you have a high voltage meter, you can measure the focus voltage to
  determine if it is being changed by the focus pot and if it is in the
  ball park (2-8 kV typical). Sometimes, the part of the flyback with the
  focus pot can be snapped off and cleaned or parts replaced but usually you
  need to replace the whole unit. There may a capacitor or two on the PCB on
  the neck of the CRT that could have increased leakage as well thus reducing
  the focus voltage.
• To determine if the CRT is the problem, for sharp focus after the unit has
  warmed up. Power-off for an hour or so and carefully pull the CRT neck board
  off of the CRT. Then, power up the unit. Let it run long enough such that
  there would have been a detectable focus drift. Now, power-down, plug the
  CRT neck board back in, and power-up. Watch the image as it appears on the
  screen:
  • If the focus starts out fuzzy and sharpens up as the image appears and
    gradually becomes sharper as the CRT warms up the CRT is likely tired.

    The only catch here is that plugging the CRT neck board into the CRT
    results in an additional load on the flyback due to the picture beam
    current which heats it more as well. Thus, if the problem takes a few
    minutes to appear, keep the brightness turned down except to check the
    appearance of the picture from time to time.

    You can set the focus control for optimum when warmed up and just turn
    the monitor on in advance of when you will be needing it or add a user
    focus adjustment by drilling a hole in the plastic case for an *insulated*
    screwdriver or flyback focus knob extender :-). The CRT may continue
    to function for quite a while so this is not impending doom.

  • If the focus is relatively stable as the image appears and increases
    in brightness *and* is about as sharp as it would be with the monitor
    warmed up, the problem is most likely in the flyback. However, also
    check for bad components or decayed (tan or brown) glue on the CRT neck
    board. A drifting flyback will need to be replaced as it will probably
    get worse and fail completely. Clean the surface of the circuit board and
    CRT socket in the vicinity of the focus and screen terminals and traces.
    Contamination or just dirt and grime can easily cause problems especially
    on humid days since the resistance of these circuits is extremely high
    (100s of M ohms).
  • If the focus is relatively stable as the image appears and increases
    in brightness *and* is similar to what it would be with the monitor cold,
    you have a very strange situation where some load on the high voltage
    power supply, perhaps, is causing a thermal problem. This would be rare.

About the quality of monitor focus

Question: I have 2 identical monitors. One is razor sharp from edge to edge.
The other is blurred at the corners- not from convergence problems,
but just plain out of focus. In this monitor, the focus adjustment on
the flyback can improve the focus at the edges, but then the center of
the screen becomes worse..My question is : Is this a problem in the
electronics and presumably a fixable flaw or is it caused by variance
in the picture tube itself and not correctable ? Or is it some other issue?

(From: Bob Myers (myers@fc.hp.com).)

The adjustment on the flyback sets the “static” focus voltage, which is
a DC voltage applied to the focus electrode in the CRT. However, a single
fixed focus voltage will not give you the best focus across the whole CRT
screen, for the simple reason that the distance from the gun to the screen
is different at the screen center than it is in the corners. (The beam
SHAPE is basically different in the corners, too, since the beam strikes
the screen at an angle there, but that’s another story.) To compensate
for this, most monitors include at least some form of “dynamic” focus, which
varies the focus voltage as the image is scanned. The controls for the
dynamic focus adjustment will be located elsewhere in the monitor, and
will probably have at LEAST three adjustments which may to some degree
interact with one another. Your best bet, short of having a service
tech adjust it for you, would be to get the service manual for the unit
in question.

It is also possible that the dynamic focus circuitry has failed, leaving
only the static focus adjust.

As always, DO NOT attempt any servicing of a CRT display unless you are
familiar with the correct procedures for SAFELY working on high-voltage
equipment. The voltages in even the smallest CRT monitor can be lethal.

Bad focus and adjustment changes brightness

This is the classic symptom of a short between the focus and screen
supplies – probably in focus/screen divider which is part of the flyback
or tripler. However, it could also be in the CRT. If you have a high
voltage meter, measuring the focus voltage will show that (1) it is low
and (2) it is affected by the SCREEN control Similarly, the SCREEN voltage
will be affected by the FOCUS control (which is what is changing the
brightness.

To determine if the problem is in the CRT, measure the FOCUS and SCREEN
voltage with a high voltage meter. If they are identical pull the plug
on the CRT. If they are now their normal values, then a shorted CRT is
a distinct possibility – see the section: Rescuing a
shorted CRT.

Charlie’s comments on focus problems

(From: Charles Godard (cgodard@iamerica.net).)

Most true focus problems that I have encountered (when the IHVT is ok) are
related to leaks or resistance on the focus output. The diming of the screen
when the focus pot is adjusted leads me to think in terms of a leaky socket.
I’d remove the ground from the crt socket to the tube dag and see if it
sparks. If so there may be a leak in the socket to ground. It could also be
leaking to another pin, such as the screen grid. A rhetorical question: What
happens to the screen voltage when the focus pot is adjusted?

I have seen sockets that had no arching or other telltale signs, leak through
the plastic housing to ground out the focus voltage.

Look closely at the screen. If the blurring is in the form of small circles,
then you have an open or hi-resistance focus electrode inside the tube. The
circles may vary in visibility with brightness.

If you still haven’t found the problem, try to confirm that this is truly a
focus problem. Remove the crt socket and observe the hi-voltage. If it
climbs more than about 1k, say all the way up to 25kv, then you may have a
beam current problem rather than a focus problem. In that case re-check all
crt board voltages. WARNING: Removing the CRT socket and powering the unit
may destroy the CRT on some models. See the section:
Warning about disconnecting CRT neck board.

If you have done all of the above and removing the socket makes no change in
the hi-voltage, then try to determine why the hi-voltage is low.

Watch the screen as the brightness, contrast, or screen control are adjusted.
See if you can observe any signs of blooming. When the IHVT doesn’t provide
enough current to satisfy the demands of the tube for current, the the picture
tends to appear to expand like a balloon. i.e., bloom. This can be caused by
not enough drive to the IHVT. Carefully monitor the b+ to the horizontal drive
stages to see that is is stable and correct.

Purple blob – or worse

Have you tried demagnetizing it? Try powering it off for a half hour, then
on. Repeat a couple of times. This should activate the internal degausser.
See the section: Degaussing (demagnetizing) a CRT.

Is there any chance that someone waved a magnet hear the tube? Remove it
and/or move any items like monster speakers away from the set.

Was your kid experimenting with nuclear explosives – an EMP would magnetize
the CRT. Nearby lightning strikes may have a similar effect.

If demagnetizing does not help, then it is possible that something shifted
on the CRT – there are a variety of little magnets that are stuck on at the
time of manufacture to adjust purity. There are also service adjustments
but it is unlikely (though not impossible) that these would have shifted
suddenly. This may be a task for a service shop but you can try your
hand at it if you get the service manual – don’t attempt purity adjustments
without one.

If the monitor was dropped, then it is even possible that the internal
shadow mask of the CRT has become distorted and you now have a seventy-five
pound boat anchor. 🙁 If the discoloration is slight, some
carefully placed ‘refrigerator’ magnets around the periphery of the tube might
help. See the section: Magnet fix for purity problems –
if duct tape works, use it!

It is even possible that this is a ‘feature’ complements of the manufacturer.
If certain components like transformers are of inferior design and/or are
located too close to the CRT, they could have an effect on purity. Even if
you did not notice the problem when the monitor was new, it might always have
been marginal and now a discoloration is visible due to slight changes or
movement of components over time.

Color rings – bullseye pattern

This probably means the degaussing circuitry is terminating suddenly instead
of gradually as it should. The most likely cause is a bad solder connection
to the degauss thermistor or posistor or something feeding it.

You can confirm this by manually degaussing the screen with the TV or monitor
turned on. If the problem disappears, the above diagnosis is probably valid.
Check for bad solder connections in the vicinity of the degauss components
and AC line input.

Magnet fix for purity problems – if duct tape works, use it!

The approach below will work for slight discoloration that cannot be eliminated
through degaussing. However, performing the standard purity adjustments
would be the preferred solution. On the other hand, the magnets may be quick
and easy. And, where CRT has suffered internal distortion or dislocation of
the shadowmask, adjustments may not be enough.

In any case, first, relocate those megablaster loudspeakers and that MRI
scanner with the superconducting magnets.

The addition of some moderate strength magnets carefully placed to reduce or
eliminate purity problems due to a distorted or dislocated shadowmask may be
enough to make the monitor usable – though it will probably not be perfect.
The type of magnets you want are sold as ‘refrigerator magnets’ and the like
for sticking up notes on steel surfaces. These will be made of ferrite
material (without any steel) and will be disks or rectangles. Experiment
with placement using masking tape to hold them in place temporarily. Degauss
periodically to evaluate the status of your efforts. Then, make the ‘repair’
permanent using duct tape or silicone sealer or other household adhesive.

Depending on the severity of the purity problem, you may need quite a few
magnets! However, don’t get carried away and use BIG speaker or magnetron
magnets – you will make the problems worse.

Also note that unless the magnets are placed near the front of the CRT, very
significant geometric distortion of the picture will occur – which may be a
cure worse than the disease.

WARNING: Don’t get carried away while positioning the magnets – you will be
near some pretty nasty voltages!

(From: Mr. Caldwell (jcaldwel@iquest.net).)

I ended up with the old ‘stuck on a desert island trick’:

I duck taped 2 Radio Shack magnets on the case, in such a way
as to pull the beam back.!!!!

A $2 solution to a $200 problem. My friend is happy as heck.

RCA sells magnets to correct corner convergence, they are shaped like chevrons
and you stick them in the ‘right’ spot on the rear of the CRT.

(From: Tom Sedlemyer (wesvid@gte.net).)

First set purity as best you can.

Obtain some pieces of refrigerator door magnet strips from an appliance
repair shop (they usually have some lying around).

Cut the strips into 1 inch pieces. Place a strip as on the bell of the
picture tube as close to the yoke as possible and in line with the corner that
has the purity error. Rotate the magnet until you correct the purity error
and tape it in place. Multiple magnet strips can be used and you may
experiment with the size of the strips for best effect. It is very important
that the strips are positioned close to the yoke or the effect will not hold.
The only drawback to this method is some very slight distortion of the
geometry of the raster, but it beats hell out of paying for a new CRT.

Color monitor only displays one color

I assume that now you have no other colors at all – no picture and no
raster. Let us say it is red – R.

It is probably not the CRT. Do you have a scope? Check for the R, G,
and B video signals at the CRT. You will probably find no signals
for the defective colors.

This is almost certainly a chroma circuit problem as any failure of the
CRT or a video driver would cause it to lose a single color – the other
two would be ok. Therefore, it is probably NOT the CRT or a driver on
the little board on the neck of the CRT.

Try turning up the SCREEN control to see if you can get a G and B raster
just to confirm that the CRT is ok.

Locate the video drive from the mainboard for the good and a bad color.
Interchange them and see if the problem moves. If so, then there is
a video signal problem. If not, it is on the little CRT board.

It could be a defective chroma IC or something else in the chroma decoder.

Disappearing Red (or other color)

Problem: I have been given an old colour TV. The reception is good, but very
often, when the contrast and brightness of the TV image is low (e.g. when
a night scene is shown), the red colour slowly disappears, leaving behind
the green and blue image and many red lines.

The remaining red retrace are the giveaway that this is most likely not
a CRT problem.

(If there were no red lines, it could be the filament for the red gun
of the CRT going on and off due to a bad connection inside the CRT – bad
news.)

How is a black and white picture? (Turn down the color control).

If B/W picture is good, then the problem is somewhere back in the chroma
decoder circuitry.

Check the video input to the CRT video driver board and signals on that board.
If B/W picture is also bad, then you can compare red and green signals
to determine where they are becoming different. The red lines in your
description sounds like the red video output circuit is drifting and messing
up the background level, blanking, screen, or other setting. Could be a
capacitor or other component.

Interference resulting in jiggling or wiggling

Note: similar symptoms can be the result of a monitor defect or running the
monitor at scan rate beyonds its capabilities. However, magnetic interference
from electrical wiring, other equipment is very common and sometimes overlooked
when looking for a complex, expensive, and obscure explanation for a
misbehaving monitor (or TV).

Also, if your outlet is not grounded, I have heard of similar symptoms under
certain conditions. Grounding IS essential for safety should a short circuit
fault develop in the PC as well as to get the most benefit from a surge
suppressor so now is a good time to upgrade!

Interference from electrical wiring

If the wiring of normal outlets is done correctly even without a safety
ground, the currents should be balanced and you will not experience a problem.
However, many circuits, particularly those involving setups like 3-way
switches or switched outlets and wiring in older buildings can have
unbalanced currents when active. If your monitors are close enough
to the wiring, there can be interference which will take the form of
a flickering or pulsating display.

Other than recommending moving the monitors, there is no easy solution.
They can be shielded with Mu Metal but that is expensive. Or you could
run all displays at a 60 Hz vertical rate (or 50 Hz depending on where
you live). However, this is inconvenient and will never be quite perfect.

If you have flexibility during construction or renovation, there are ways to
minimize the chance of unexpected behavior later:

Think of it this way: If the sum of the currents in the cable are zero, there
will be no magnetic field to worry about. This will be the case for normal
110 VAC branch circuits.

Some sources for magnetic interference:

• Three (or more) way circuits – lamps or fixtures controlled from more than
  one location which use a ‘traveler’. In this case, a single energized wire
  runs between switches and/or the switches and the load.
• Circuits which do not have their return in the same cable. For example,
  ceiling fixtures controlled from a wall switch but where the Hot comes
  from another location. Or, a string of baseboard heaters fed from opposite
  ends.
• Circuits which share a Neutral but where one or more of the Hots are not in
  the same cable. This is more likely to be found in old construction using
  knob-and-tube wiring where circuits were just connected in the most
  convenient way.
• Loops in Neutral and Ground conductors. The way circuits are supposed to
  be wired (U.S.A. at least) is nearly always in a star sort of configuration
  where the Neutral and Ground conductors never connect at the ends of the
  ‘star’. However, due to poor wiring practices, it is quite possible for
  Neutrals to be connected to other Neutrals or Grounds to be connected to
  other Grounds or for them to be cross connected at various locations – all
  without any other symptoms. This can even happen between buildings. See
  the section: Interference from cross-connected
  buildings. However, the likelihood of this sort of fault isn’t
  that great.

First confirm that the problem is due to inside wiring – shut off all power to
the building (if possible) or at least switch off each circuit in turn to see
if the problem disappears (run the monitor from a UPS or a remote outlet).

• If the symptoms persist, check for external sources of interference
  (although there could still be a Ground-Neutral loop formed by the connection
  between G and N at the service panel or to other buildings. In this case,
  the effect would likely be strongest near the service panel.). See the
  section: Interference from power lines.
• If the symptoms are gone, try to narrow down the circuit or circuits that
  are responsible by switching each one on individually.

In all cases, running the Hots and Neutrals for the circuit in the same cable
(or at least in close proximity) will avoid this problem as the total current
will sum to zero.

Realistically, you would have to be very unlucky to have a noticeable problem
in residential wiring except near the service panel or high power appliances
like baseboard heaters, equipment with large motors or transformers, etc.

Interference from power lines

Power lines (any size from local distribution to large intercontinental
transmission lines) nearby can result in noticeable effects to monitors as a
result of the magnetic fields surrounding the individual wires – similar to
that from unbalanced inside wiring (see the section:
Interference from electrical wiring.
TVs may not be affected, at least not as much, since they
will be running at a vertical rate almost the same as the power line
frequency).

The severity of the effects will vary depending on the load distribution on
the three (probably) phases, distance, orientation with respect to the
monitor, etc. Moving the monitor as far from the offending power lines as
possible, experimenting with its orientation, and seeing if you can live with
a vertical scan rate equal to the power line frequency, are the only realistic
options other than constructing an expensive mu-metal box for it. Check out
MuShield specifically under “Monitor
Enclosures” if you’re curious. Less EMF,
Inc. sells Mu-metal foil by the foot but what they have listed is rather
thin – I don’t know how well it would work for monitor CRT shielding.

Interference from cross-connected buildings

Here is a rare case where the neighbor was really at fault (in a historical
sort of way).

(From: Tuyen Tran (ttran@ziplink.net).)

Get this: my house and my neighbor’s house were grounded together, so we
connected to the power company’s neutral in two places. The way I understand
it, this caused a ground loop between our two panels. My neighbors used to own
this place. When they built a small house next door, instead of digging a
separate well, they just ran a 3/4 inch copper pipe between my water tank and
their new place. (This place used to be a dairy farm, so it had plenty of
water capacity.) When they installed their panel, the electrician of course
bonded their water pipes to the panel, which then connected our two grounds
together. When they sold the place, they put in their own well, but nobody
bother to cut the original pipe linking the two houses together. It’s been
like this for at least 40 years; I’m the third owner!

So I took a pipe cutter to the thing, and no more interference.

Interference from other equipment

Any type of equipment which uses or generates strong magnetic fields can
interfere with a monitor. Other computer monitors or TVs, equipment with
power transformers, and electric motors will cause a pulsating or flickering
display. Loudspeakers or other equipment with static magnetic fields will
cause color purity and/or geometric distortion problems which degauss will
not cure.

The easiest way to confirm that interference is your problem is to move
the monitor or suspect equipment to a different location. The only real
solution is to separate the monitor and interfering device.

Note that with scan rates that are not even near the power line frequency
any more, a variety of symptoms are possible including shimmering, wiggling,
undulating (how many more adjectives can you come up with?). The rate
of the movement will be related to the difference between the monitor scan
rate and the frequency of interference.

My monitor is possessed!

Problems are that all graphics applications fade to black, lose their color
on parts of the screen, and there are strange pincushion problems on the
right side of the monitor? This all came up suddenly, with no apparent
changes your my part.

You tried changing video drivers, modes, cleaning connections on
cables and video card, even pulled the card and cleaned the edge
connector.

After cleaning up, things seemed to work (still had pincushion
problem), but next time it was powered on, same weird problems.

Voodoo might be required but more down-to-earth causes are likely:

Are you sure nothing changed in the building (like you installed a medical
MRI unit with a 2T magnet in the same room)?

All monitors have a built in degauss circuit which operates when power
is turned on after being off for at least 15 minutes or so. This could
have failed – it is switching off suddenly instead of ramping down as it
should – and is making the problem worse or you could have a power supply
failure inside the monitor.

Gradual variations in color or brightness on the screen or over time
are almost always monitor problems, not video card, software, or cables.

It won’t hurt to try manual degauss with the monitor powered, see below.
If this clears it up – possibly until you turn the power off and on again, then
it may be the internal degauss circuitry.

Shimmering image due to vibrations

If your monitor uses a Trinitron or clone CRT, then this may be normal.
Even with the 1-3 unsightly stabilizing wires running across the screen,
the vertical aperture grille wires in a Trinitron type CRT can wiggle as
a result of mechanical shocks or vibration. Any movement results in
momentary changes in color purity, color balance, brightness. Gently tap
on the side of the monitor and you may see the same effect.

Wiring transmitted interference

The power that comes from the wall outlet is supposed to be a nice sinusoid
at 60 Hz (in the U.S.) and it probably is coming out of the power plant.
However, equipment using electric motors (e.g., vacuum cleaners), fluorescent
lamps, lamp dimmers or motor speed controls (shop tools), and other high power
devices, may result in a variety of effects.

While monitors normally include some line filtering, the noise immunity varies.
Therefore, if the waveform is distorted enough, some effects may show up even
on a high quality monitor.

Symptoms might include bars of noise or distortion moving slowly or rapidly up
or down the screen or diagonally. This noise may be barely visible as a couple
of jiggling scan lines or be broad bars of salt and pepper noise, snow, or
distorted video.

The source is probably local – in your house and probably on the same branch
circuit – but could also be several miles away.

• One way to determine if the problem is likely to be related to AC power
  is to switch your vertical scan rate to match the power line frequency:
  60 Hz in the U.S., 50 Hz in most European countries, etc. If the pattern
  of noise or distortion is now stationary (or at most slowly drifting up
  or down the screen), the interference is likely power line related:
  • A single bar would indicate interference at the power line frequency.
  • A pair of bars would indicate interference at twice the power line
    frequency.

  Either of these are possible.

• Try to locate the problem device by turning off all suspect equipment to
  see if the problem disappears.
• The best solution is to replace or repair the offending device. In the
  case of a light dimmer, for example, models are available that do a better
  job of suppressing interference than the typical $3 home center special.
  Appliances are supposed to include adequate noise suppression but this is
  not always the case.

  If the source is in the next county, this option presents some significant
  difficulties :-).

• Plugging the monitor into another outlet may isolate it from the offending
  device enough to eliminate or greatly reduce the interference.
• The use of a line filter may help. A surge suppressor is NOT a line
  filter.
• Similar symptoms could also be produced by a defective power supply in the
  monitor or other fault. The surest way of eliminating this possibility is
  to try the monitor at another location.

Jittering or flickering due to problems with AC power

If you have eliminated other possibilities such as electromagnetic
interference from nearby equipment or electric wiring or a faulty video
card or cable – or software – then noisy or fluctuating AC power may be
a possibility. However, modern monitors usually have well regulated power
supplies so this is less common than it used to be. Then again, your
monitor may just be overly sensitive. It is also possible that some
fault in its power supply regulator has resulted in it becoming more
sensitive to minor power line fluctuations that are unavoidable.

One way to determine if the problem is likely to be related to AC power
is to run the monitor on clean power in the same location on the same
computer. For example, running it on an Uninterruptible Power Source
(UPS) with the line cord pulled from the wall socket would be an excellent
test. The output of the UPS’s inverter should be free of any power line
noise. If the monitor’s image has now settled down:

1. Large appliances like air conditioners, refrigerator, or washing machines
   on the same circuit might cause significant power dips and spikes as they
   cycle.

   Plugging a table lamp into the same outlet may permit you to see any obvious
   fluctuations in power. What else is on the same circuit? Depending on
   how your house or apartment is wired, the same feed from the service panel
   may be supplying power to widely separated areas.

2. For some unfathomable reason, your monitor may just be more sensitive to
   something about the power from the circuit in that room. There may be
   nothing actually wrong, just different. While unlikely, a light dimmer
   on the same circuit could be producing line-conducted interference.

   If you have a multimeter, you could at least compare the voltages
   between the location where it has problems and the one where it is
   happy. Perhaps, the monitor is sensitive to being on a slightly
   different voltage. This might only be a problem if some circuitry
   in the monitor is marginal in some respect to begin with, however.

3. There could be a bad connection somewhere on the circuit. If your house
   has Aluminum wiring, this is a definite possibility.

   Try a table lamp since its brightness should fluctuate as well. This
   should be checked out by a competent electrician as it represents a real
   fire hazard.

An electrician may be able to pinpoint the cause but many do not have
the training or experience to deal with problems of this sort. Certainly,
if you find any power line fluctuations not accounted for by major
appliances, on the same circuit this should be checked by an electrician.

My monitor has the shakes

You turn on your monitor and 5-10 seconds later, the display is shaking or
vibrating for a second or so. It used to only occur when first turned on,
but now, the problem occurs 3 times in 30 seconds. Of course, many
variations on this general theme are possible.

Some possibilities:

1. Defective degauss circuit – this would normally cause a shaking or
   vibration when you first turn it on but you normally do not notice it
   since the CRT is not warmed up. The degauss circuit may have developed
   a mind of its own.
2. Other defective circuitry in monitor – power supply regulation, deflection,
   or bad internal connections.
3. External interference – did you change anything or move your setup
   recently? See the sections on: “Interference from other equipment”,
   “Interference from electrical wiring”, and “Interference from power lines”.
4. Defective video cable (unlikely). Wiggle the VGA cable to be see if
   you can induce the problem.
5. Loose trim magnets of other magnetic components on or near deflection yoke.
   This is somewhat rare but if the adhesive comes apart, the magnetic fields
   from the deflection current can cause the parts to vibrate which will
   result in a jitter or movement of the picture. There may even be audible
   crackling or snapping sounds associated with this vibration.

Fred’s comments on monitor interference problems

(From: Fred Noble) Fred_Noble@msn.com).)

Monitors are very susceptible to electromagnetic fields. If any of the
following is “yes” it may point to an ‘electrical’ cause of the Monitor
problem.

• Do you have a ceiling fan in the same room turned on?
• Do you have a wireless telephone in the room?
• Do you get similar effects on your TV?
• Are you near a large transformer, substation, or high voltage overhead wires?
• Is your computer located close to the meter on the other side of the wall?
• Do you have speakers next to the monitor? Are they shielded?
• Do you have a phone or other device with a magnet in it near the monitor?
• Is the cabling routed too near a printer cable?
• Do you have a surge/power strip or UPS near your monitor?

Reposition the monitor or move it to a different location. Also make sure that
you are turning the monitor on first and then the system to ensure that the
video card is properly recognizing the monitor.

Check cable connections (make sure no other cables are crossing the monitor
cable. If you have an extension on the monitor output cable then remove it as
well.

Try swapping out the monitor to verify if it really is the monitor or take
your monitor to another system and see how it responds there.

If you are plugging the monitor into a surge strip, remove it from there and
plug the monitor directly in the wall outlet.

Discussion:

There might be an ambient RFI/EMI electrical or magnetic field present around
your computer location. Some of the electrical field or the conducted RFI/EMI
electrical “noise” causes are considered here.

Rough summary of excessive magnetic & electric fields:

• Cause: Electrical wiring errors.

  Electrical wiring errors such as inappropriate or non-NEC code neutral
  to ground bonds in the facility (not at the common bus in the mains), and
  other non-NEC Code wiring that results in the HOT wire fields not being
  OFFSET by the neutral wire fields.

  Incorrect wiring will be aggravated (and will be noticed first) on a circuit
  where there is an Air Conditioner, copier, laser printer.

  Correction: This is an electrical problem that has resulted in a *net
  current* flowing in the facility and is also a shock hazard.

  Don’t use devices that dump current onto the neutral line, and have an
  electrician correct the wiring to NEC code.

• Cause: Magnetic flux linkages.

  It is normal for transformers to use magnetic flux linkages (to couple
  primary to the secondary).

  Correction: Keep transformer based equipment away from sensitive equipment.

  There are other corrective measures here that can be discussed on the design
  level and on the application level.

  If the transformer is used to power a “noisy” load (high harmonics) perhaps
  a good harmonic filter can be used between the transformer and the load
  (example a good UL 1283 noise filter or Surge suppressor with UL 1283
  filter).

• Cause: Motors also use magnetic flux linkages in normal usage.

  Correction: Keep large, active, motors away from sensitive equipment (and
  try to keep them on a different circuit if possible).

  The use of a good harmonic filter on that circuit will help reduce the
  harmonics (for example, a good surge suppressor with a UL 1283 RFI/EMI
  filter, or a Line Conditioner).

• Cause: UPSs, especially when on inverter (during brownout or blackout)
  create magnetic & electric fields.

  Correction: Keep them away from sensitive loads, and advise manufacturer of
  problems encountered with the UPS.

  The UPS may have a faulty inverter circuit or part, or may be in need of a
  re-design.

Loss of color after warmup

If there is a general loss of picture but there is light on the screen
if the brightness is turned all the way up, then this is a video input,
video amplifier, RGB driver, or power supply problem.

If it recovers after being off for a while, then you need to try a cold
spray in the video/controller to identify the component that is failing.
Take appropriate safety precautions while working in there!

If it stays broken, then most likely some component in the video circuitry,
controller, or its power supply as failed. There is a good chance that
it is a bad colder connection – the trick is to locate it!

Miscellaneous Problems

Contour lines on high resolution monitors – Moire

These fall into the category of wavey lines, contour lines, or light and dark
bands even in areas of constant brightness. (Some people may refer to this
phenomenon as “focus or Newton’s rings”.) These may be almost as fine
as the dot pitch on the CRT or 1 or 2 cm or larger and changing across the
screen. If they are more or less fixed on the screen and stable, then
they are not likely to be outside interference or internal power supply
problems. (However, if the patterns are locked to the image, then there
could be a problem with the video board.)

One cause of these lines is moire (interference or beat patterns) between the
raster or pixels and the dot structure of the CRT. Ironically, the better the
focus on the tube, the worse this is likely to be. If the individual pixels
do not cover enough phosphor dots, then the actual color and brightness
displayed won’t match what the video card is generating and this will depend
on the actual location of the pixel relative to the phosphor dots.
Trinitrons, which do not have a vertical dot structure should be immune to
interference of this sort from the raster lines (but not from the horizontal
pixel structure). Slot mask CRTs (not that common on monitors) also have
fewer problems with vertical moire.

You can test for moire by slowly adjusting the picture size. If it is moire,
you should see the pattern change in location and spatial frequency as slight
changes are made to size. Changes to position will move the patterns along
with the picture without altering their character and structure significantly
(though fine detail will change).

If they are due to the raster line structure – your focus is too good – the
patterns will remain essentially fixed in position on the face of the CRT
for horizontal size and position adjustments – the patterns will remain
fixed under the changing image.

How to eliminate it? If moire is your problem, then there may be no easy
answer. For a given resolution and size, it will either be a problem or
not. You can try changing size and resolution – moire is a function
of geometry. Ironically, I have a monitor which is nicer in this respect
at 1024×768 interlaced than at 800×600 non-interlaced.

Some monitors have a ‘Moire Reduction Mode’ switch, control, or mode. This
may or may not be of help. One way to do this is – you guessed it – is to
reduce the sharpness of the beam spot and make the picture fuzzier! Another
approach adds a high frequency dither to the beam spot position which may
result in a headache! You might find these cures to be worse than the
disease.

Another cause of similar problems is bad video cable termination
creating reflections and ghosting which under certain conditions can be so
severe as to mimic Moire effects. This is unlikely to occur in all colors
with a VGA display since the termination is internal to the monitor and
individual resistors are used for each color (RGB).

I think it is ironic that some people will end up returning otherwise superb
monitors because of moire – when in many cases this is an indication of most
excellent focus – something many people strive for! You can always get rid of
it – the converse is not necessarily true!

Moire and shadow mask dot pitch

(From: Bob Myers (myers@fc.hp.com).)

The density of the holes in the shadow mask set an upper limit on the
resolution supported by that monitor. Lower resolutions work just fine;
there is no need to have the logical pixels in the image line up with the
physical holes in the mask (nor is there any mechanism to make this happen),
and so you can think of this as the “larger pixels” of the lower-res image
simply covering more than one hole or slot in the mask.

As the effective size of the pixels in the image approach the spacing of
the mask holes, individual pixels are no longer guaranteed to cover enough
phosphor dots on the screen to ensure that they are constant color or constant
luminance, but an image will still be displayed which ON AVERAGE (over a
reasonably large area) looks OK. Actually, the specified “top end”
format (“resolution”) for most monitors usually is at or slightly beyond
this point – the effective pixel size is somewhat UNDER the dot pitch.

Sources of external interference that can affect the monitor display

The following list is just some of the ways your picture can get screwed up
through no fault of the monitor. It’s sort of amazing they work as well as
they do! Most of these are discussed in greater detail in subsequent
sections.

Static/DC magnetic fields:

• Unshielded/inadequately shielded multimedia speakers
• Stereo loudspeakers
• MRI scanner next door.

Transient magnetic fields:

• Kid’s (or adults) playing with magnets
• Electro-Magnetic Pulse (EMP) from nearby lightning strike or nuclear blast
• Changing monitor location or orientation without degaussing.
• Shift in Earth’s magnetic field every 10-20K years. 🙂

AC magnetic fields (usually at power line frequency):

• AC or DC wall adapters/transformers
• Fluorescent lamps (magnetic ballast)
• Laser printer and other peripherals
• TV, VCR, DVD, or other A/V equipment
• Additional computer monitor(s) too close
• Large appliances including furnace, A/C, fridge, microwave
• Wiring in walls (unbalanced load/shared Neutral)
• Wiring in electrical service panel
• Outside wiring and power distribution equipment

Radio Frequency Interference:

• High power radio transmitter nearby (broadcast, military, amateur)

Power Line Transmitted Interference:

• Lighting on dimmers (incandescent/halogen lamps/fixtures)
• Motor speed controls (ceiling fans)
• Fluorescent lamps (all types)
• Vacuum cleaners/shop equipment/other brush type motors
• Equipment using switchmode power supplies
• Heavy industry down the street

Interference affecting video signal:

• Lack of earth/safety ground (line filter ineffective)
• Ground loop caused by PC and monitor plugged into different circuits
• Cross connected buildings resulting in ground loop

Interference between monitor and VCR or TV

“I’ve got a desktop computer with a VGA monitor above it. To the left of
it (a few inches away), I have a VCR with a Commodore composite monitor
above it (1084 model). I don’t have Cable TV or anything special, just a
simple antenna connected to the VCR to pick up the two local TV stations.

The reception is pretty good with the computer off, but the problem arises
when I turn the computer on. The VCR is already plugged into a different
outlet than the computer. Since I am into video production, I need this
setup as it is laid out (close together).

So, how can I shield the VCR from the interference from the computer? Can
I do something with the antenna to make the signal stronger, or can I
place some kind of material between the VCR and computer?”

Your PC is a serious RF emitter. Areas of leakage include the case as well
as the possibly the monitor and cable. Turn off the monitor and/or unplug
the video cable to see if it is the latter.

You PC’s case may not have adequate shielding. Better cases have grounding
fingers and proper RF shielding throughout – that is one reason they are
more expensive. This may be an option.

The VCR may be picking up the interference internally or via its antenna.

There may be some options but you first need to determine where the
interference is coming from and where it is being picked up.

Cable installed upside-down – now monitor does not sync correctly

“I have an old vga monitor that I screwed up. I plugged it into the vga
card upside down. Now I know that seems impossible, but believe me, it isn’t.

Now the vertical is fine, but the horizontal is all screwy. (is that a word?
screwy?) It’s about 8″ wide and can’t be adjusted to normal size.

The result is a very, um, interesting image. Is it possible that I did
some minor damage like blowing a cap, diode, or horizontal transistor?”

I’ll give you 100:1 odds that you bent the H sync pin and it is now bent over
and not inserted in its hole. Remove the connector, and examine the pins – if
this is the case, take a pair of needlenose pliers and **very carefully**
straighten it out. If it was pushed in, grab hold and pull it out to
the same length of the other pins and if necessary, put a drop of adhesive
at its base to prevent it from being pushed in again. If it breaks off or
is unreachable, you will need to replace the connector (unless the shell
comes apart which is usually impossible or at least not easy on newer
monitors).

Isolated spots on display

These could be a problem with the video source – bad pixels in the video
card’s frame buffer or bad spots on a camcorder’s CCD, for example.
Or, they could be dirt or dead phosphor areas in the CRT. Except for
problems with the on-screen character generator, it is unlikely that the
monitor’s circuitry would be generating isolated spots.

You can easily distinguish between video problems and CRT problems – missing
pixels due to the video source will move on the screen as you change raster
position. CRT defects will remain stationary relative to the screen and will
generally be much more sharply delineated as well.

There is a specification for the number and size of acceptable CRT blemishes
so you may have to whine a bit to convince the vendor to provide a replacement
monitor under warranty.

Power saving problems

Modern monitors are usually designed to permit software to control
various levels of power saving (‘green’) features from blanking the screen
to totally shutting down. Problems can occur if the software to control
these features is not compatible with the monitor or not set up
correctly or is attempting to control a monitor that lacks power saving
modes or is defective or incompatible.

A monitor that behaves normally under most conditions but emits a
high pitched whine when the computer attempts to direct it into power
saving mode is probably not understanding the commands or does not have
the appropriate power saving features. It probably behaves about the
same as if there is no video signal – which indeed may be the case as
far as it is concerned.

Many monitors not receiving proper sync signals are perfectly happy
driving everyone in the office insane with that high pitched whine.
Others will blow up eventually.

Recommendation: Don’t use power saving until you have the proper software
and you know what your monitor supports. Of course, your monitor could be
defective and your current software is actually fine. Check your user manuals
to determine compatibility and setup parameters. Also see the sections:
Monitor life, energy conservation, and laziness
and Implications of power saving modes.

Monitor drift?

Problem: I have a 17″ monitor that has an image that EVER SO SLIGHTLY drifts
to the left (and stops) after a long day’s work (heat, I suppose). Also,
the vertical height shrinks a little bit. Is this at all normal/acceptable?

How much is ‘ever so slightly’? There are a fair number of components whose
values could alter the position/size of a monitor image. I do not find it
at all surprising that there should be a small shift due to heat. It really
depends on many factors including the basic design, quality of components,
ventilation/cooling, etc. Of course, it is possible to have a monitor that
has a component that is worse with respect to temperature. Could also
be related to line voltage depending on the regulation of your monitor’s
power supplies.

In general, my feeling is that if it is not objectionable (a 1/2″ shift
would be objectionable) AND it’s severity is not changing with time, you
can ignore it.

Many monitors do this. TVs do this but you are not aware of it since they
are already 5-10% overscanned for just this reason, as well as compensating
for component aging and line voltage fluctuations.

A can of cold spray or a heat gun will be useful to track down the bad
component but it could be a frustrating search.

Monitor shuts down or goes blank at certain scan rates

It could be the monitor’s components have drifted and are now marginal
at your one or more of your scan rates. However, first check with an
oscilloscope if possible to confirm that your horizontal and vertical
timing are indeed as expected.

Some video cards modify horizontal and vertical frequency as part of their
software size adjustment in their Setup program. For example, with ATI
cards, even though the general resolution option in the DOS Install program
may be 800×600 at 75 Hz, adjusting the horizontal size can actually vary the
horizontal frequency over a greater than 10% range. A similar variation
is possible with the vertical rate.

Does just the picture go away or does power die to the monitor? If
you can see the neck of the CRT, the filaments glow orange when it is
operating. Does this glow disappear indicating that the deflection/HV
is shutting down?

There could be a number of possibilities – no way of knowing if it
will be easy or inexpensive to repair without testing. It could be
power supply, HV supply, X-ray protection, etc.

Monitor flickers when disk accessed

This is almost certainly a software problem. First, try moving the monitor
away from the PC as far as the cable will stretch. If it still occurs,
then it is probably not the monitor. Could have to do with power saving
(just a guess) or some other incompatibility. Nothing the PC does should
affect the monitor in any way once the refresh rate is set.

Buzzing monitor

Do you actually mean buzz – low frequency as in 50 – 120 Hz? Or,
do you really mean high pitched whine. If the latter, see the section:
High pitched whine or squeal from monitor with no
other symptoms.

• If it is from inside the monitor – make sure it is not your multimedia
  speakers or sound card picking up interference – it is in the deflection
  (probably vertical) or power supply. Either of these can vary in severity
  with picture content due to the differing current requirements based on
  brightness. It could be a power supply transformer, deflection yoke, or
  other magnetic component. Even ferrite beads have been caught buzzing when
  no one was looking. 🙂 Any of these parts could vibrate if not anchored
  securely or as they loosen up with age.

  Some hot-melt glue, RTV silicone, or even a strategically wedged toothpick
  may help. A new part may or may not quiet it down – the replacement could
  be worse! For yoke noise, see the section:
  Reducing/eliminating yoke noise.

• There is a slight possibility that the AC power in your home or office has
  some harmonic content – the waveform is not sinusoidal. This might be the
  case if you try to run on the same circuit as an active dimmer or something
  else with thyristor control. Proximity to heavy industry could also cause
  this.

  Relocating the offending device to another branch circuit may help. You
  could also try a line conditioner (not just surge suppressor) which includes
  filtering. Else, petition to have that paper manufacturer move out of the
  neighborhood :-).

• Sometimes, it is simply a design or manufacturing defect and the only
  alternative is a replacement – possibly a different brand. It may be more
  difficult to quiet down a buzz than a high pitched whine.
• Some monitorss are simply poorly designed. You cannot infer the severity
  of this annoyance from any specifications available to the consumer. It is
  strictly a design (e.g. cost) issue. The size of the monitor is not a
  strong indicator of the severity of the problem but there will be some
  relationship as the power levels are higher for larger units. The best you
  can do is audition various monitors very carefully to find one that you are
  satisfied with.
• One those rare monitors that have a cooling fan, its bearings may be worn
  or in need of cleaning and lubrication, or a blade may be hitting something.

High pitched whine or squeal from monitor with no other symptoms

Sometimes this is continuous. In other cases, it comes and goes almost as
though there is an intelligence at work attempting to drive you crazy. All
the more so since a technician may not even be able to hear what you are
complaining about if their hearing is not as sharp at high frequencies as
yours. Even high resolution computer monitors running at high horizontal scan
rates (beyond human hearing) can have these problems due to the switching
power supplies as well as subharmonics of the horizontal scan rate exciting
mechanical resonances in the magnetic components or even a portion of the
sheetmetal used for shielding if in close proximity to a magnetic component.

If it is a new monitor and you think the sounds will drive you insane,
returning it for a refund or replacement may be best alternative. However,
you may get used to it in time.

Note: if the whine only occurs when the monitor is unplugged from the computer
or the computer is turned off, this is probably normal. Without valid sync
signals the monitor defaults to a horizontal rate which is within the audible
range (less than 20 kHz). Any vibrating components will be readily heard.
It is usually not a sign of impending failure.

In most cases, this sound, while annoying, does not indicate an impending
failure (at least not to the monitor – perhaps to your mental health) or
signify anything about the expected reliability of the unit though this is not
always the case. Intermittent or poor connections in the deflection or power
supply subsystems can also result in similar sounds. However, it is more
likely that some part is just vibrating in response to a high frequency
electric current.

There are several parts inside the monitor that can potentially make this
noise – the horizontal flyback transformer and to a lesser extent, the
deflection yoke and associated geometry correction coils would be my first
candidates. In addition, transformers or chokes in the switching power
supply if this is distinct from the horizontal deflection circuitry.

You have several options before resorting to a 12 pound hammer:

• Confirm that the horizontal scan rate being used by the video card is
  well within the range supported by the monitor. If it isn’t, change it
  to be a one that is – in addition to possible whining, this is stressful
  on the deflection and power supply and may result in an expensive repair
  in a very short time. Even if the scan rate is supposed to be fine,
  changing it slightly (e.g., 5 percent) might help just because it shifts
  the deflection frequency away from a mechanical resonance. However, this
  may not be a long term solution.
• As much as you would like to dunk the monitor in sound deadening
  insulation, this should be avoided as it will interfere with with proper
  cooling. However, the interior of the computer desk/cabinet can be lined with
  a non-flammable sound absorbing material, perhaps acoustic ceiling tiles.
  Hopefully, not a lot of sound energy is coming from the front of the monitor.
• Move the monitor out of a corner if that is where it is located – the
  corner will focus sound energy into the room.
• Anything soft like carpeting, drapes, etc. will do a good job of absorbing
  sound energy in this band. Here is your justification for purchasing those
  antique Persian rugs you always wanted for your computer room :-).

If you are desperate and want to check the inside of the monitor:

• Using appropriate safety precautions, you can try prodding the various
  suspect parts (flyback, deflection yoke, other transformers, ferrite beads)
  with an insulated tool such as a dry wooden stick. Listen through a
  cardboard tube to try to localizing the source. If the sounds changes, you
  know what part to go after. Sometimes a replacement flyback will
  cure the problem unless it is a design flaw. You do not want to replace
  the yoke as convergence and other adjustments would need to be performed.
  Other transformers can be replaced.
• Sometimes, tightening some mounting screws or wedging a toothpick between
  the core and the mounting or coils will help. Coating the offending part
  with sealer suitable for electronic equipment may quiet it down but too much
  may lead to overheating. A dab of hot-melt glue or RTV silicone may help.
  Even replacement is no guarantee as the new part may be worse. For yoke
  noise, see the section: Reducing/eliminating yoke
  noise.
• A few monitors have internal cooling fans. The whine may be due to worn or
  dry bearings. If this is the case, the fan must be serviced as it is not
  likely doing it job and damage due to excessive temperatures may eventually
  be the result.

Note that the pitch of the whine – the frequency – may not even be audible
to a technician assigned to address your complaint. The cutoff frequency
for our hearing drops as we get older. Someone over 40 (men more so than
women), you may not be able to hear the whine at all (at least you can look
forward to silence in the future!). So, even sending the monitor back for
repair may be hopeless if the technician cannot hear what you are complaining
about and you are not there to insist they get a second opinion!

Monitor whines in power saving (standby) mode

(From: Bob Myers (myers@fc.hp.com).)

In standby, the monitor is not being supplied with horizontal sync, and
so the horizontal deflection circuits are free-running. (If they’re still
powered up in a given monitor design when in standby mode, that is; there
are no standards governing what actually gets shut down in the various
power-saving states.) It’s likely that in this case, the horizontal is
free-running at a frequency which is audible, and you’re hearing a whine
from a vibrating transformer core (for example, the flyback). This will NOT
have anything to do with the timing used when the monitor is on and running
normally, so it’s no surprise that changing the refresh rate didn’t affect
this.

You can either have a technician try to track down the offending component
and try to keep it from making the noise (usually by adding some “goop” to
prevent or at least reduce the audible effects of the vibration), or you
might try (if your system permits it) using one of the other power-management
states instead of standby. Removing BOTH the horizontal and vertical
sync signals places the monitor in the “off” condition (I’m assuming
compliance to the VESA DPMS standard throughout this discussion), in which
just about everything should be shut down. However, since this will remove
the heater supply from the CRT as well, it WILL take longer to recover from
the off state.

Reducing/eliminating yoke noise

(From: Terry DeWick (dewickt@esper.com).)

Carefully look under vertical core next to plastic liner, on top and bottom is
a plate called the astigmatism shunt, it has come loose. Work RTV, epoxy, or
service cement onto it to glue it down and noise should quit.

(From: TVman (tvman@newwave.net).)

I have fixed a total of 27 of these sets with noisy yokes by removing the
yokes and using motor armature spray sealant.

If you carefully mark the EXACT position of everything (yoke, purity magnets),
and slide the yoke off the CRT, then once the yoke has been sealed with motor
armature spray sealant and has dried thoroughly, put the yoke back EXACTLY
where it was, there should be no problems.

The only thing I have had to do was set the purity on one set, but it
was off a little to begin with.

Monitor was rained on

Was the monitor plugged in when the leak started? Any piece of equipment with
remote power-on capability has some portions live at all times when plugged
in and so there may have been damage due to short circuits etc. Substantial
damage could have already been done.

Otherwise, you may just need to give it more time to dry out. I have
had devices with keypads getting wet that required more than a week but
then were fine. There are all kinds of places for water to be trapped and
take a long time to evaporate.

If the monitor got wet while unplugged or it has a mechanical (hard) on/off
switch, then give it a lot of time to dry out completely. Assuming all
visible water is drained, a week represents a minimum safe time to wait.
Don’t rush it.

Generally, some moisture will not do any permanent damage unless the
unit was on in which case you will simply have to troubleshoot it the
old-fashioned way – one problem at a time.

You may be tempted to use a hair drier or heat gun to speed the process
along. But, be extra careful not to do damage
to the equipment. Slightly melted laptop keyboard
is an example of a bit of overkill. As far as I know, this was due to
a short exposure to a properly functioning blow drier. The owner swears that
the blow drier is not overheating and that she hasn’t been able to set her
hair on fire. I can just imagine what would have happened with a real heat
gun. They just don’t make those keys the way they used to! 🙂

Monitor was dropped

If your work area is maintained like that of Nedrie in the movie “Jurassic
Park”, you might not even notice if one of your monitors fell off the table!
This is no way to treat a monitor.

However, mishaps do happen.

Assuming it survived mostly intact – the CRT didn’t implode, you could
still have a variety of problems. Immediately unplug the monitor!

If you take it in for service, the estimate you get may make the national
debt look like pocket change in comparison. Attempting to repair anything
that has been dropped is a very uncertain challenge – and since time is
money for a professional, spending an unknown amount of time on a single
repair is very risky. There is no harm is getting an estimate (though
many shops charge for just agreeing that what you are holding was once a
monitor, or was it a fish tank?)

This doesn’t mean you should not tackle it yourself. There may be
nothing wrong or very minor problems that can easily be remedied. The
following are likely possibilities:

1. Cracked circuit boards. These can be repaired since monitors usually have
   fairly wide open single or two sided boards.
2. Broken circuit components. These will need to be replaced.
3. Broken solder connections particularly to large heavy components
   on single sided boards. Reflow the solder. If the trace is cracked
   or lifted, repair as in (1).
4. Broken mounting brackets. These are usually made of cheap plastic
   and often don’t survive very well. Be creative. Obtaining an
   exact replacement is probably not worth the trouble and expense.
5. Components knocked out of line on the CRT envelope or neck – deflection
   yoke, purity magnets, convergence magnets and coils, geometry correction
   magnets. These will need to be reattached and/or realigned. Some CRTs use
   little magnets glued to the funnel portion of the CRT envelope. If any
   of these have come loose, it could be quite a treat to figure out where
   they went and in what orientation.
6. Internal damage to the CRT – popped or distorted shadow mask, misaligned
   electron guns. Unfortunately, you will probably have no way of
   identifying these since you cannot see inside the CRT. They will not
   be apparent until all other faults have been remedied and the TV set
   is completely realigned. At that point, extremely severe purity or
   convergence problems that do not respond to the normal adjustment
   procedure would be one indication of internal damage. Give the TV a
   nice funeral.

If you still want to tackle a restoration:

As noted, unplug the monitor even if it looks fine. Until you do a thorough
internal inspection, there is no telling what may have been knocked
out of whack or broken. Electrical parts may be shorting due to a broken
circuit board or one that has just popped free. Don’t be tempted
to apply power even if there are no obvious signs of damage – turning
it on may blow something due to a shorting circuit board.

Then, inspect the exterior for cracking, chipping, or dents. In addition
to identifying cosmetic problems, this will help to locate possible areas to
check for internal damage once the covers are removed.

(At this point, most people will assume there is no interior damage and
plug the set back in and turn it on. My recommendation is to resist
this temptation since as noted, this could result in further damage
making the repair more expensive if there are circuit problems. However,
if the unit was on at the time of the “incident” or you are really
determined to get to the conclusion and would just throw the thing in
the trash if it doesn’t work or blows up, go for it! But, if you’re the
more cautious type, continue with the systematic diagnosis and repair
procedure that follows.)

Next, remove the cover. Confirm that the main filter capacitors are
fully discharged before touching anything. Check for mechanical problems
like a bent or deformed brackets, cracked plastic parts, and anything that
may have shifted position or jumped from its mountings. Inspect for loose
parts or pieces of parts – save them all as some critical magnets, for
example, are just glued to the CRT and may have popped off.

Carefully straighten any bent metal parts. Replace parts that were
knocked loose, glue and possibly reinforce cracked or broken plastic.
Plastics, in particular, are troublesome because most glues – even plastic
cement – do not work very well. Using a splint (medical term) or sistering
(construction term) to reinforce a broken plastic part is often a good
idea. Use multiple layers of Duco Cement or clear windshield sealer
and screws (sheetmetal or machine screws may be best depending on the
thickness and type of plastic). Wood glue and Epoxy do not work well
on plastic. Some brands of superglue, PVC pipe cement, or plastic hobby
cement may work depending on the type of plastic.

Inspect for any broken electronic components – these will need to be replaced.
Check for blown fuses – the initial impact may have shorted something
momentarily which then blew a fuse.

There is always a risk that the initial impact has already fried electronic
parts as a result of a momentary short or from broken circuit traces and
there will still be problems even after repairing the visible damage and/or
replacing the broken components. This is most likely if the monitor was
actually on but some modern monitors have circuitry that is energized at
all times. (If power is controlled by a tiny tiny pushbutton this is the
case.)

Examine the circuit boards for any visible breaks or cracks. These will
be especially likely at the corners where the stress may have been greatest.
If you find **any** cracks, no matter how small in the circuit board, you
will need to carefully inspect to determine if any circuit traces run
across these cracks. If they do, then there are certainly breaks in
the circuitry which will need to be repaired. Circuit boards in consumer
equipment are almost never more than two layers so repair is possible but
if any substantial number of traces are broken, it will take time and patience.
Do not just run over them with solder as this will not last. Use a fine
tipped low wattage soldering iron and run #22-26 gauge insulated wires
between convenient endpoints – these don’t need to be directly on either
side of the break. Double check each connection after soldering for correct
wiring and that there are no shorts before proceeding to the next.

If the circuit board is beyond hope or you do not feel you would be able
to repair it in finite time, replacements may be available but their cost
is likely to be more than the equipment is worth. Locating a junk unit of the
same model to cannibalize for parts may be a more realistic option.

Degauss the monitor as any impact may magnetize the CRT. Power cycling may
work but a manual degaussing is best.

Once all visible damage has been repaired and broken parts have been replaced,
power it up and see what happens. Be prepared to pull the plug if there
are serious problems (billowing smoke or fireworks would qualify).

Perform any purity, convergence, or other realignment as needed.

Then proceed to address any remaining problems one at a time.

Really cleaning a monitor inside and out

(From: Dr. Ludwig Steininger (drsteininger@t-online.de).)

Often I get defective monitors, which are more than 5 years old, and have been
run in offices for 8 to 10 hours/day. So, their case and pcbs usually are very
dirty and dusty.

What do I do (it’s no joke!): After removing the case I carefully put them in
a bath (on a flexible layer) and let them have a intensive shower of pure cold
water (for 1 to 2 minutes). Additionally, the case is cleaned with soap or a
detergent containing liquid (being careful, not to spill to much of it onto
the PCBs). After rinsing with fresh clear water, dust and other kinds of dirt
are removed and the monitors look new again. Then I allow all drops of water
to run off. This can effectively be supported by turning the monitor on
another side from time to time (duration: approximately 1 hour). Before
turning on AC again, I let the wet monitor dry in ambient air for about 2 days
(in the sunshine this can be finished in 1 day only).

This procedure has been applied for many monitors. I’ve never had any bad
experiences (it’s very important to wait, until the pcbs are really dry!).
Considering this experience, I just can’t imagine, that it might not be
possible, to “save” a TV set or computer monitor, which has been drowned or
some liquid has been spilled, and AC has been plugged off ASAP (although I’ve
never had such a case). I think, that in such a case, it’s important to have a
rapid shower in order to prevent corrosion and deposits.

By the way: I know a German company, which uses water from cleaning PCBs of
computer hardware for cleaning them after being contaminated by smoke from
a fire.

So, in case of spillage, one has nothing to loose. Just try to shower your
monitor or TV set!

Setup menus will not go away or hieroglyphics on screen

Both these problems could be caused by a faulty microcontroller or
its associated circuitry. However, bad connections in the vicinity
of the controller logic could also be at fault.

Unless you see something obvious, you will need schematics.

Setup Adjustments Lost

Many modern monitors have RAM, somewhat like the CMOS SETUP memory in your PC,
that store all factory adjustments. When power is lost, there is power
surge, lightning strike nearby, nuclear detonation or EMP, it may
have put bad information into the ram and thrown it out of adjustment. There
is a way to get into the service mode (depress and hold a secret button
down and turn set on, special combination of buttons on the remote, etc.)
and then use the remote to reinitialize and adjust the problems out.

HOWEVER, IF YOU DON’T KNOW WHAT YOU DOING YOU COULD GIVE YOURSELF WORSE
PROBLEMS. YOU COULD EVEN BLOW THINGS OUT WITH SOME MONITORS!

The service manual will be essential to have any chance of successfully
reinitializing everything without causing damage due to incorrect settings.

If it’s not an adjustment problem you probably have a bad part – somewhere.

If you do manage to get into the setup menu and are willing to take the
risk without service information, try not to make any unnecessary changes
and document every change you make!!! That way you can go back if you do
anything wrong (hopefully).

Monitor doesn’t work after being in storage

So the monitor you carefully stuffed in a corner of the garage is now totally
dead. You swear it was working perfectly a year ago and just have to get
that state-of-the-art Commodore 64 up and running!

Assuming there was absolutely no action when you turned it on, this has
all the classic symptoms of a bad connection. These could be cold/cracked
solder joints at large components like transformers, power resistors, or
connectors and connectors that need to be cleaned or reseated. By ‘no action’
I mean not even a tweet, bleep, or crackle from anything.

To narrow it down further, if careful prodding of the circuit board(s) and
various large components with a well insulated stick does not induce the set
to come on, even momentarily, check the following:

1. Locate the horizontal output transistor. It will be in a TO3 metal
   (most likely on an older set) or TOP3 plastic package on a heat sink.
   With the set unplugged, confirm that there is no voltage across C to E and
   then measure between them with an ohmmeter. In at least one direction it
   should be fairly high – 1K or more. This confirms that the HOT is
   probably good.

   (There is also a slight chance that there is a low voltage regulator
   in addition to the horizontal output, so don’t get them confused. The
   horizontal output transistor will be near the flyback transformer and
   yoke connector.)

2. Trace back from the HOT collector to the flyback and through the flyback
   to the B+ feed from the power supply. Clip a voltmeter between this point
   and the HOT emitter. Make sure the leads are well insulated and can’t
   accidentally short to anything. (This test can be performed across C to E
   of the HOT but if the horizontal deflection were to start up unexpectadly,
   the meter could be damaged by the high voltage pulses on the HOT collector.
   But if you can’t find the B+ source, it may be worth the risk.) Plug it
   in and turn it on.
   • If the problem is in the low voltage (line) power supply, there will
     be no substantial voltage across C-E.

     You should be able to trace from the power line forward to find the bad
     part though a schematic will help greatly.

   • If the problem is in the startup circuit or horizontal oscillator/driver,
     then there will be something on the order of 100 to 160 V across C-E.

     In this case, a schematic may be essential.

Note: don’t assume that the metal parts of the chassis are ground – they
may be floating at some line or B+ potential. Also, the HOT emitter may
not be connected directly to ground.

Cheap monitors with multiple intermittent problems

If the monitor is a non-name or the company has since gone belly up (no
surprise, right?) you may have a monitor with one of those circuit boards
best described as bad solder joints held together with a little copper.
In this case, prodding with an insulated stick and the use of a few select
4 letter words may get it going. The circuit boards may be double sided with
what were called ‘rivlets’ for vias. The rivlets were relatively massive –
literally little copper rivets – and they were not adequately heated or
tinned during assembly so there were bucketloads of cold solder joints
that show up during middle age. I repaired one of these by literally
resoldering top and bottom of every one of the darn things with a high
wattage iron. Or, the soldering just may be plain, well, horrible. Carefully
going over every connection is the only solution. Sometimes, removing the
solder from suspect joints, cleaning both the component lead and trace, and
then resoldering will be needed if corrosion has set in.

Monitor has burning smell

Assuming there are no other symptoms:

If this appears after extended operation – an hour or more – it may
just be a build up of dust, dirt, and grime over the years. After
understanding the safety info, some careful vacuuming inside may help.
Just don’t be tempted to turn any screws or adjustments!

Dust is attracted to the high voltage section in particular – even the
front faceplate of the CRT collects a lot and should be wiped with a damp
cloth from time to time.

If the symptoms develop quickly – in a few minutes or less, then there
could still be a dust problem – a power resistor may be heating a wad of
it but other possibilities need to be considered.

If not dust, then probably in the power supply but realize that TVs don’t
have a nice metal case labeled ‘power supply’. It is just a bunch of stuff
scattered around the main board. Without identifying the part that is
heating, a diagnosis is tough especially if the set really does
work fine otherwise. However, if a series regulator were faulty and putting
out too much voltage, the set could appear to work properly but in fact
have excessive power dissipation in certain components. If cleaning the dust
does not solve the problem, you will probably need a schematic to identify
the correct voltages.

Static discharge noise and picture tube quality

This question came up with respect to a large screen TV but may apply to large
screen monitors as well.

“I bought a 29” TV a couple of weeks ago and I have noticed that after being
switched on for > about 15/20 minutes, whenever the picture changes from a
“light” scene to a darker scene, the set makes a crackling noise. It sounds
as though there has been a build-up of static and it is being discharged. I
have never noticed this in a TV before and I was wondering if this is normal
and acceptable behaviour for a large-screen TV?”

It probably is normal. Whether it is acceptable is a personal matter. In
some geographic areas no countermeasures are taken at all…

When the scene changes from bright to dark, the beam current is reduced to
practically zero. As a result, the high voltage rises. (The high voltage
supply has a relatively high internal impedance.) The high voltage is
connected to the inside layer of the picture tube. A voltage change on the
inside will also cause a voltage change on uncovered parts of the outside,
especially on the part of the picture tube that is hidden under the deflection
coils. This causes little sparks between the picture tube surface and the
inside of the deflection coils and this is accompanied by a crackling sound.

On the better picture tubes, a dark “anti-crackle coating” is painted on the
picture tube near the deflection coil. This is a very high impedance coating,
dark black, much darker than the usual aquadag coating over the rest of the
picture tube. You should be able to see the difference.

If, on the other hand, the outside of the picture tube near the deflection
coil is not coated then you have a problem. Then you will hear strong
crackling also at switch-on and switch-off. Normally you shouldn’t see such a
‘cheap’ picture tube on the European market…

The area of the picture tube around the anode connector is also not coated,
for obvious reasons. Normally that should not cause any significant
sound. Same goes for the front of the screen and neither should the anode
cable crackle.

In a dark room you should be able to see from the tiny blue flashes where the
sound comes from. This is perhaps best observed at switch-on and switch-off
(with a black picture on the screen). Try and keep the back cover mounted !

Loudspeakers and monitors

Loudspeakers incorporate powerful magnets – the larger the speaker, the
larger the magnet. However, anyone who goes ballistic when the mention
is made of a loudspeaker near a TV or monitor, should take their Valium.

The fringe fields outside the speaker box will not be that great. They
may affect the picture perhaps to the point of requiring degauss. The
normal degauss activated at power-on will usually clear up any color purity
problems (assuming the loudspeakers have been moved away). At worst, manual
degauss will be needed. The CRT will not be damaged. The maximum
field – inaccessible at the voice coil – is quite strong. However, even
for non-shielded loudspeakers, the magnetic field decays rapidly with
distance especially since the core structure is designed to concentrate
as much of the field as possible in the gap where the voice coil travels.

Speakers specifically designed for use with multimedia computers have (or
should have) specially shielded magnet structures or an additional magnet with
its field set up to cancel the main magnet’s fringe field which will minimize
these effects. Nonetheless, if you see any indication of discoloration, move
them to a greater distance.

However, keeping unshielded (e.g., megawatt stereo) speakers away from
CRTs is a good idea.

Now, you really should keep your superconducting magnetic resonance imager
magnet at least in the next room…..

Should I replace all the electrolytic capacitors if I find a bad one?

When a bad capacitor is found in a monitor, the question of course arises
as to the likelihood of other capacitors going bad in short order.
It might be worth checking (other) caps in the power supply or hot
(temperature) areas but you could spend you whole life replacing **all**
the electrolytics in your older equipment!

Black powder being generated inside monitor?

You have just noticed a black powder spontaneously appearing from inside
your computer monitor. What is it? The monitor seems happy as a clam.

Well, it is probably just air-born dust that is collecting there due to
the air flow in your area and high voltage static fields. The monitor is
acting like an electrostatic dust precipitator. If there were really black
powder being generated inside, I would expect you would smell something
really really bad and the monitor would not continue to be happy.

Sweet little old ladies and TVs from attic

The following story is specifically for a TV but the same applies to any
electronic servicing. Always confirm the customer’s complaints first!!

Then verify that everything else works or you will never know if your
efforts have affected something unrelated.

(Original request from rogerj@apex.com):

“A sweet little old lady has duped me into repairing her old G.E. 13” color
TV. Wanted me fix bad volume pot….. “oh it has such a good picture”…
she says.

Stupidly w/o even turning it on, (big mistake) I begin to open the set.
After 15-20 min. of travail, I discover that a previous “repairman” has glued
the case shut!

Now w/ set open, I turn it on and this picture is LOUSY. Bad color, and very
poor convergence. But I don’t know if I’m to blame for banging it around
trying to open it up. Also, no hor. or vert. hold. (fixed that w/a few caps)
This things probably been sitting around for a few years.”

Well, you certainly did not kill the caps. Anything that sits for a few
years – probably in a damp unheated attic – is suspect.

Did you find the adjustments on the yoke assembly tight? If so, you probably
did not move anything very much either. She may remember the good picture
it produced before being stuffed away in the attic.

“Anyway after going through all the adjustments, the convergence at the sides
is still bad and the horizontal size is a tad insufficient (w/no adjustment
available)”

Could be that the convergence (including pincushion) circuits are still
faulty – not just misadjusted.

Other things that can effect horizontal size while still giving you a complete
picture:

1. Voltage to horizontal output transistor low. Is there a voltage regulator
   in your set? The one I have has none. I assume your line voltage is ok.
2. Increased resistance or inductance of the yoke windings. For all
   you know, the yoke may have been replaced with the wrong part.
3. Yoke improperly positioned on tube neck.
4. Excessive high Voltage. This is usually not adjustable.

I bet the thing hasn’t worked properly in 10 years.

Disposing of dead monitors (CRTs and charged HV capacitors)

I don’t know what the law says, but for safety, here is my recommendation:

Treat the CRT with respect – the implosion hazard should not be minimized.
A large CRT will have over 10 tons of air pressure attempting to crush it.
Wear eye protection whenever dealing with the CRT. Handle the CRT by the
front – not the neck or thin funnel shaped envelope. Don’t just toss it
in the garbage – it is a significant hazard. The vacuum can be safely
released (Let out? Sucked in? What does one do with an unwanted vacuum?)
without spectacular effects by breaking the glass seal in the center of the
CRT socket (may be hidden by the indexing plastic of the socket). Cover the
entire CRT with a heavy blanket when doing this for additional protection.
Once the vacuum is gone, it is just a big glass bottle though there may be
some moderately hazardous materials in the phosphor coatings and of course,
the glass and shadow mask will have many sharp edges if it is broken.

In addition, there could be a nice surprise awaiting anyone disconnecting the
high voltage wire – that CRT capacitance can hold a charge for quite a while.
Since it is being scrapped, a screwdriver under the suction cap HV connector
should suffice.

The main power supply filter caps should have discharged on their own
after any reasonable length of time (measured in terms of minutes, not
days or years).

Of course around here, TVs and monitors (well, wishful thinking as I
have yet to see a decent monitor on the curb) are just tossed intact
which is fortunate for scavengers like me who would not be happy at
all with pre-safed equipment of this type!

Apple/Sony monitor dies after variable length of time

The following discussion relates to failures of the X-ray protection tap
on a Sony part affectionately known as the ‘big red cap’ or the HSTAT
block in some Sony manufactured monitors.

“This is a (Apple) Sony 13″ monitor, 4 years old. After being turned on
for 30 minutes, the display goes completely blank and the front LED goes
off. If the power is shut off for 10 minutes or so, it will come back on
for another 15 minutes or so, then go blank again, etc. The +120v and
+65v from the power module is still present when it blanks out, but no
other voltages (+12, +960, etc) are present on the main circuit board.
I’ve been told it might be the HV capacitor is bad; would like to hear a
2nd or 3rd opinion before buying a new capacitor.”

That is the same diagnosis a friend of mine got for her monitor with that
identical problem. Replacing the capacitor did fix the problem.

That ‘big red capacitor’ is a Sony part which includes some kind of low
voltage sense connection as well. It is used to shut the monitor or TV
down should the HV increase resulting in increased risk of X-ray generation.
Unfortunately, the resistors inside often go bad causing the unit to shut
off erroneously. The guy at the place where she got it repaired said that
the capacitor is one of the most common problems with those monitors. $70
for the part + $50 for labor, ouch!

These used to be only available from Sony. Why can’t Sony design monitors
like everyone else? Sure, I know, theirs are better (well, except for the
unsightly stabilizing wires on Trinitrons!). Now, however, less expensive
replacements can be had at places like Computer Component Source.

For testing, it may be possible to disconnect the sense output. With shutdown
disabled, the monitor should continue to run BUT WITH NO X-RAY PROTECTION.
Therefore, this should only be used for testing – a replacement will be
required.

Note: On some models, the sense wires need to be connected during startup
or else it will never come on.

CAUTION: On some models (like the Sony CPD1302), the sense signal may be used
for actual HV regulation. Thus, if the sense wire is disconnected, (or the
divider inside the Hstat block fails open) there is no feedback and it is
possible for the high voltage (and probably B+) to increase until the HOT
(and possible other components) blow.

(From: Duke Beattie (beattie@wsu.edu).)

The low voltage connection of the ‘big red cap’ is part of the “X-ray
protection” circuit. If the high voltage to the crt goes to high it is
supposed to shut down the whole thing. Unfortunately the sensor inside
goes bad and puts out the wrong voltage and that shuts down the world.
The part is available at “Computer Component Source” for about $30, it is
a “M041″ (Sony/Apple part number” These things go out with great regularity.
So if your Apple monitor shuts down this is probably the culprit.

(From: A.R. Duell (ard12@eng.cam.ac.uk).)

On some of the older Trinitrons (certainly on the 13″ Trinitron monitor
I have), the HSTAT pot is connected as a potential divider on the EHT
supply. The slider of the pot is connected to the static convergence
electrode, but a tap on the lower end of the pot goes to the protection
circuit. Something like this:

            Static Conv Electrode
                  o 
                  |
                  V
    EHT---------/\/\/\-------\/\/\---+---\/\/\-----+
                                     |             |
                                     o            _|_
                                 Protection      ///

If the EHT rises too high, then the voltage at the protection point also
rises, and a shutdown signal is sent to the scan processor.

All those resistors are encapsulated in the HSTAT block which has an EHT
input from the flyback, a Coaxial EHT output (EHT and Hstat electrode) to the
CRT, an earth wire, and a 2 core cable (earth and Protection) that goes
to the scan board.

Unfortunately, if those resistors change in value, then the protection
circuit may operate even at the normal EHT voltage. And as they’re all
potted in one block, you have to change the complete unit.

(From: Neil brown (nbrown@whispa.co.nz).)

When your monitor works do you see faint diagonal white line on it?

If so the cutoff need adjusting and it will cause the symptoms you
describe exactly, If it doesn’t come on after a “rest” then yes it may be a
bad cap but I have realigned a lot more than I have replaced HV caps!

Also on the adjustment board there is a resister that goes and pushes the
cutoff up high, from memory it is a 1 M resister and it drifts up high.

More on the Apple/Sony ‘big red capacitor thing’

(From Terry L. Wright (terryl@wolfenet.com).)

The big red thing has been called a capacitor, a voltage tripler and a
diode assembly not to mention other less polite names. It is in fact at
the root of the failure in this monitor but does not necessarily need to be
replaced. You will find a low voltage shielded wire comes from the red
block. It goes to a four lead jack and plug which connects to the main
board. The two pins that the shielded cable goes to are marked ground and
Href, short for high voltage reference. If these two pins are shorted
together the unit will no longer shut off by itself.

Why does this work? Because the red block contains a voltage divider, the
output of which tells the main board if the 25 Kilovolt supply to the crt
goes too high. When the red block ages the relative values of the internal
resistors changes and the block output increases. The main board
interprets this as excessive high voltage and shuts the horizontal output
down to protect the circuit and ostensibly to protect from Xrays. By
shorting the output you can force the main board to assume that the voltage
is not too high. Note that you have also disabled any protection that the
circuit may have provided from Xrays or high voltages. Personally I do not
care about this as I have never seen this monitor fail in any way to cause
excessive second anode voltage.

Editor’s note: failure (open) of a snubber capacitor across the HOT is one
failure that can result in excess high voltage. Thus, I would consider this
a temporary ‘for testing’ solution unless you add some other mechanism for
detecting excess high voltage. First confirm with a high voltage probe that
the monitor isn’t shutting down properly – due to excess high voltage! In
addition, the original problem may get worse and eventually affect the
convergence and other functions of the Hstat unit. — sam

(From: David J. Pittella (ddc_pitt@ix.netcom.com).)

I spent 8 years working for a very large Apple authorized service provider.

The original 13″ Model MO-401 (not the MO401LL/B) actually had a bad run of
these high voltage capacitors. Apple did have a warranty extension on specific
date ranges of these parts, I would doubt this is still in effect … but you
could check.

The ‘big red’ high voltage capacitor is Apple P/N 910-0058, it is mounted
to the bottom of the chassis on this display. This part connects between
the flyback and the anode connector on the CRT, there is also small grey
cable from this device to the “D” (main) board.

The “C” board (on the neck of the crt) is notorious for cold solder joints
on the CRT connector. I would always resolder these whenever I worked on
this display.

CTX monitor intermittent or blows fuse

Initial symptoms are erratic startup or shutdown sensitive to temperature
or vibration. Eventually, the monitor will go totally dead if the original
problems are not dealt with.

Look for a vertically mounted daughterboard. This board contains an IC
UT3842 which is the pulse width modulator IC for the switcher supply. ECG
makes a replacement although I don’t have the number handy. Make sure
you check associated parts on this card for damage, as this circuit
usually fries pretty well.

The entire cause of these problems is generally bad solder joints on the
back side of that daughter board. Unsolder it from the main board, and fix
those first. Where a connector is used (P104) resolder this as well. Then
replace Q101, the 18 V zener next to it (ZD101), and the .39 ohm resistor if
necessary. Note: The zener is for protection only. Therefore its exact
voltage rating is not critical – anything over about 6 V will work.

(From: Keith Scott (kscott@news.HiWAAY.net).)

Exactly! Every 14 or 15″ CTX I’ve worked on had the MOSFET, zener and the
low ohm resistor toasted. BTW, they use the low ohm resistor as a fuse to
keep them catching on fire when the other stuff shorts out.

(From the editor).

Once the fuse blows, several parts have gone belly-up and will need to be
replaced in addition to the soldering of the daughter board.

(From: Bill Rothanburg (william.rothanburg@worldnet.att.net).)

Replacing the fuse will not fix the monitor. The odds are rather overwhelming
that you have been bit by the infamous CTX ‘daughter board with bad solder
joint’ flaw. If you have the ability to handle a soldering iron, order the
repair kit from CCS (1-800-356-1227). This will contain all of the parts
and instructions on fixing this problem. IMPORTANT!!! Remove the daughter
board, resolder all of the joints on the connector, and reinstall the daughter
board.

CCS sells a kit for $13.99, includes 2SK955, 1N5248 18V zener, .39 R, and
fuse. #07-1512 800 356-1227 They also warn of solder breaks on plug
of daughter board. The service manual is available from CTX for $15,
800 888-2120 (compared to $50 from CCS!!).

Gateway Crystalscan and MAG monitor problems

The following applies to several Gateway monitors including the CS1572FS (very
common) and CS1776LE, as well as similar models from MAG (who is the actual
manufacturer of these Gateway monitors).

“I have a Gateway CS1572 FS monitor. Recently, a high pitched whine
accompanied by faint dark lines scrolling from top to bottom appeared.
Initially the problem disappeared after a warm-up period, but now it is
constant. Can anyone give me info on: solving similar problem, or a
source for schematics on this type of monitor. Gateway wants me to send
it to MAG, but that sounds like big $$$.”

Other related symptoms: Wiggling raster, possibly only at higher scan rates.

R331 is a common failure in the power supplies of Gateway CS1572 monitors.
Apparently, a number of other models also use this design, and got the same
batch of bad resistors :-).

It is supposed to be 91K. 1 W but gradually increases in value until regulation
is compromised. While it is marked 1%, hand selecting a 5% metal film resistor
that is within tolerance will work fine and even this may not be needed as
the voltage adjustment pot is in series with R331. Therefore, if you have
the adjustment procedure, a 1% resistor is unnecessary in any case. Then,
adjust the B+ to the value marked.

Note: It is probably a good idea to replace R331 for these symptoms even if
it tests good. In some cases, it would appear that these resistors fail at
full voltage but not when tested with a multimeter.

If symptoms persist, check ZD302 (12.2 V?).

While you are in there, check for bad solder connections or damage to R302
and Q105 (swivel base hits these).

Allergies from monitors?

Aside from eye, back, or finger strain, there may be two possible sources
of actual chemical/gaseous emissions:

1. The materials used in some of the electronic components as well as the
   plastics of the case can outgas – possibly for quite some time after
   manufacture. This is made worse due to the heat inside.
2. Ozone production. This is caused by electrical discharges – corona – from
   various high voltage terminals. Ozone really shouldn’t be a problem with a
   monitor in good condition but it is possible. And, as a monitor ages and
   collects all sorts of dirt and dust, it is more likely.

Items of Interest

Web sites with monitor specifications

Of the half dozen or so Web sites that I used to have for extensive monitor
information, only Monitorworld has survived as far as I can tell:
They still have the important specifications for a wide variety of
monitors indexed by manuracturer and model:

I am only recommending this site for the information on
monitor specifications, not necessarilly for other products or services
since I haven’t evaulated them. Note that since this data comes from
undetermined sources, it isn’t always to be accurate.
Sorry for the lack of additions Web sites but believe it or not, I am not
usually informed when any particular company goes belly-up or their Marketing
department decides that fluff is more important than substance and they pull
the plug on the pages with useful information. 🙁

How do multiscan monitors determine and store the scan parameters?

With modern SVGA multiscan monitors, once a particular resolution and scan
rate is set up, there is rarely a need to readjust size, position, and other
parameters. How is this accomplished?

(From: Bob Myers (myers@fc.hp.com).)

It’s different for different designs, of course, but in general today’s
‘digitally controlled’ monitors recognize various timing modes by counting
the horizontal and vertical sync pulses to determine the line scan and
vertical refresh rates. Any input within a certain tolerance of a recognized
pair of frequencies here is assumed to be that timing, and a set of stored
numbers corresponding to that timing are then read from a memory and used
to set up the adjustments. In most of these monitors, the various adjustable
parameters – size, centering, etc., – are controlled by voltages coming from
a set of D/A converters, so the stored information is basically just a table
of numbers that get sent to the D/As when that timing is recognized.

The number of both factory and user presets available varies from product
to product, of course, but there’s usually somewhere between 8-15 of each.
The exact number is going to depend on how much memory is available, and how
many different parameters need to be controlled for each recognized timing.

Unless the output of the graphics controller is an exact match for the
timing used at the factory when the preset information was generated, there
may still be slight errors, for obvious reasons. Fortunately, the widespread
acceptance of timing standards (such as those produced by VESA) are
reducing the severity of this problem.

Monitor reliability with SVGA

There are parts in the monitor which may get hotter with SVGA but if it is
designed for SVGA resolution, there should be no problem (assuming you are
not running in an excessively hot room or with the ventilation holes covered).

A good quality auto-scan monitor should not mind switching screen resolutions
frequently (though doing it every few seconds continuously may stretch this
a bit).

Newer auto-scan monitors should also be smart enough not to blow up if
you feed then a scan rate which exceeds their capabilities. However,
there are a lot of poorly designed monitors out there.

If it is supposed to run SVGA, use it at SVGA. If it blows up,
switch to a different brand. There are a lot of crappy monitors being
sold on their own and bundled with PCs.

How high a refresh rate should I use?

It is the vertical refresh rate that impacts display appearance. The visual
effect of too low a vertical scan rate is excessive flicker.

Up to a point, higher is better. Everyone agrees that appearance improves
up to at least 70-75 Hz (vertical) non-interlaced but beyond this point is a
hotly debated issue (and a topic for a never ending discussion on your
favorite Internet newsgroup). The use of interlaced scanning can reduce
apparent flicker for a given scan rate for typical gray scale or color images
but may result in annoying flickering or jumping of fine horizontal lines in
graphics and text displays.

In any case, you must not exceed the maximum scan rate specs of your monitor.
See the section: Web sites with monitor specifications
if in doubt. Also, very high refresh rates may result in decreased graphics
performance particularly with DRAM based video cards due to bus contention
between the PC memory accesses and the video readout to the RAMDAC.

And, a horizontal scan rate below the specified limits may blow the HOT
instantly.

For the discussion below, the key words are “well designed”. There are a lot
of mediocre monitors out there!

(From: Jeroen H. Stessen (Jeroen.Stessen@philips.com).)

The dissipation in the deflection coils rises sharply with the horizontal scan
frequency. The horizontal scan frequency is of course higher at higher
resolution and higher vertical refresh rates. But the monitor will have been
designed to handle that, unless you don’t permit adequate ventilation.
Component failure occurs often during mode-switching, not due to keeping the
monitor in one mode or another.

It is a popular myth that a (well-designed) monitor could be damaged by
connecting it to a signal source with frequencies that are out of range. These
will be (should be) automatically blocked by the sync circuitry and you will
simply not get a stable picture. There will be no damage, and if there would
be (most likely from a too LOW line frequency) then it would be done
immediately. No need to rush setting things right.

So my advice would be to go ahead, use whatever resolution you like. The
acceleration of the wear will be insignificant, you’ll probably want a better
monitor long before it is technically worn out. If you want to be kind to
your monitor, then keep the contrast below maximum, use a black-screen
screen saver and keep the dust and smoke and moisture and grease away.

Number of colors and monitor type

“I have a CTX CVP-5468 that will not do more than 16 colors in windows. It
is being driven by an Orchid Kelvin 64 VLB board, but had the same problem
with an ATI card. When using it in linux under x-windows the same thing and
more than vga and it goes blurry and very pixelated.”

It is really not possible for this to be a monitor problem as the signals
are analog – continuous – the monitor displays whatever it is given and
does not even know the color depth except to the extent that cards are often
set up via software to use different scan rates for different color depths
(bits/pixel) often due to hardware memory/bandwidth limitations.

For the ATI in particular, I know that you can use ATI’s DOS Install program
to set it up for each resolution and mode – try this. I bet your monitor
is fine.

Various video standards

Here is a link:

Monitors, humans, and flicker

(From: Bob Myers (myers@fc.hp.com).)

The flicker-fusion frequency for emissive displays such as
CRTs cannot be given as a single number applicable to all people, all
displays, and all ambient conditions. It is dependent on the
particular individual, the size and brightness of the display (and
the characteristics of the phosphor, if a CRT), the viewing distance,
and the ambient lighting conditions.