PC Hardware in a Nutshell, 3rd Edition [Electronic resources] نسخه متنی

16.4 Troubleshooting Display Problems

Troubleshooting CRT monitors versus
FPDs begins with similar steps, but diverges due to the differing
natures of the two display types. The first troubleshooting steps are
similar for either display type: power down the system and display
and then power them back up; make sure the power cable is connected
and that the outlet has power; verify that the signal cable is
connected firmly to both video adapter and display and that there are
no bent pins; verify that the video adapter is configured properly
for the display; try the problem display on a known-good system, or
try a known-good display on the problem system; and so on. Once
you've tried the
"obvious" troubleshooting steps, if
the problem persists, the next steps you take depend on the type of
display. The following sections cover basic troubleshooting for CRT
monitors and FPDs.

16.4.1 Troubleshooting CRT Monitors

Monitors
seldom fail outright without obvious signs, such as a loud snap or a
strong odor of burning electrical components. Most monitor problems
are really problems with the power, video adapter, cable, or
hardware/software settings. To eliminate the monitor as a possible
cause, connect the suspect monitor to a known-good system, or connect
a known-good monitor to the suspect system.

If the monitor is the problem, it is often not worth repairing. If
the monitor is out of warranty, parts and labor may cost more than
buying a new monitor, which also gives you better specs and a
warranty. About the only monitors we'd even consider
repairing out of warranty are high-end 19-inch and 21-inch models,
and even there the economics are dubious.

Even if the monitor is in warranty, the shipping costs may exceed the
value of the monitor. For example, shipping a monitor both ways can
easily cost $75 or more. If that monitor is a year-old 17-inch model,
you're probably better off spending $150 on a new
17-inch monitor than paying $75 to fix the old one. Monitors have
many components, all of which age together. Fixing one is no
guarantee that another won't fail shortly. In fact,
that happens more often than not in our experience.

Never disassemble a monitor. At best, you'll likely destroy the monitor. At worst, it may destroy you. Like televisions, monitors use extremely high voltages internally, and have large capacitors that store that energy for days or even weeks after the monitor is unplugged. Robert once literally burned a screwdriver in half when working inside a color television that had been unplugged for several days. Also, the large, fragile tube may implode, scattering glass fragments like a hand grenade. People who repair monitors and televisions for a living treat them with great respect, and so should you. If you must repair a monitor, take it to someone who knows what he is doing. You have been warned.

Here are some common monitor problems:

Check the obvious things first. Verify the monitor is plugged in (and
that the receptacle has power), the video cable is connected to the
video card, the computer and monitor are turned on, and the
brightness and contrast settings are set to the middle of their
range. If none of these steps solves the problem, your monitor, video
card, or video cable may be bad. Check the suspect monitor on a
known-good system or a known-good monitor on the problem system.

If you have ACPI or APM power management enabled, it may be causing the problem. Some systems simply refuse to wake up once power management puts them to sleep. We have seen such systems survive a hardware reset without restoring power to the monitor. To verify this problem, turn off power to the system and monitor and then turn them back on. If the monitor then displays an image, check the power management settings in your BIOS and operating system and disable them if necessary.

This is a hardware problem. The flyback transformer or high-voltage
circuitry is failing or has failed. Take the monitor to be repaired,
or replace it.

This is a hardware problem with one of the electron guns. Take the
monitor to be repaired, or replace it. This problem may also manifest
as a strong color cast during normal operation that is not
correctable using the normal color balance controls.

Catastrophic monitor failure is imminent. The noises are caused by
high-voltage arcing, and the smell is caused by burning insulation.
Unplug the monitor from the wall before it catches fire, literally.

There are two likely causes. First, you may be driving the monitor
beyond its design limits. Some monitors display a usable image at
resolutions and/or refresh rates higher than they are designed to
use, but under such abuse the expected life of the monitor is
shortened dramatically, perhaps to minutes. To correct this problem,
change video settings to values that are within the
monitor's design specifications. Second, the power
receptacle may be supplying voltage lower than the monitor requires.
To correct this problem, connect the monitor to a different circuit
or to a UPS or power conditioner that supplies standard voltage
regardless of input voltage.

This is usually a minor hardware problem. The most likely cause is
that the signal cable is not connected tightly to the monitor and/or
video card, causing some pins to make contact intermittently or not
at all. Verify that no pins are loose, bent, or missing on the cable
or the connectors on the monitor and video card, and then tighten the
cable at both ends. If that doesn't fix the problem,
open the computer, remove the video card, and reseat it fully.

Another possible cause is that some hardware DVD decoder cards
"steal" one color (usually magenta)
and use it to map the DVD video signal onto the standard video
signal. Short of replacing the DVD decoder card with another model
that doesn't do this, the options are to live with
the problem or to connect the monitor directly to the video card for
normal operations and connect the monitor to the DVD decoder card
only when you want to watch a DVD. Alternatively, consider removing
the DVD decoder card. If your current video adapter includes hardware
DVD support, or if you upgrade to such an adapter, you
don't need a DVD decoder card.

The most likely cause is that the monitor is receiving inadequate
power. Connect it to a different circuit or to a backup power supply
that provides correct voltage regardless of fluctuations in main
voltage.

The most likely cause is that the refresh rate is set too low. Change
the refresh rate to at least 75 Hz. Flicker also results from
interaction with fluorescent lights, which operate on 60 Hz AC and
can heterodyne visually with the monitor. This can occur at 60 Hz
(which is far too low a refresh rate anyway), but can also occur at
120 Hz. If you're running at 120 Hz refresh and
experience flicker, either use incandescent lighting or reset the
refresh rate to something other than 120 Hz.

The video card settings are likely outside the range supported by the
monitor, particularly if you have just installed the monitor or have
just changed video settings. To verify this, restart the system in
VGA mode. If the system displays a VGA image properly, change your
display settings to something supported by the monitor.

Most modern monitors can display signals at many different scan
frequencies, but this doesn't mean that the monitor
will necessarily automatically display different signals at full
screen and properly aligned. Use the monitor controls to adjust the
size and alignment of the image.

Depending on the monitor, video card, and video settings, this may be
normal behavior, adjustable using the monitor controls. If the
distortion is beyond the ability of the controls to correct, the
problem may be with the video card, the monitor, or the driver. First
try changing video settings. If the problem persists at several
settings, move that monitor to a different system (or use a different
video card) to determine whether the problem is caused by the monitor
or video card. Repair or replace the faulty component.

This is usually caused by RF interference from another electrical or
electronic device, particularly one that contains a motor. Make sure
such devices are at least 3 feet from the monitor. Note that such
interference can sometimes penetrate typical residential and office
walls, so if the monitor is close to a wall, check the other side.
Such image problems can also be caused by interference carried by the
power line or by voltage variations in the AC power supply. To
eliminate interference, plug the monitor into a surge protector.
Better still, plug it into a UPS or power conditioner that supplies
clean power at constant voltage.

The monitor may need to be degaussed. A monitor that sits in one
position for months or years can be affected even by the
Earth's very weak magnetic field, causing distortion
and other display problems. Exposing a monitor to a strong magnetic
field, such as unshielded speakers, can cause more-extreme image
problems. Many modern monitors degauss themselves automatically each
time you cycle the power, but some have a manual degauss button that
you must remember to use. If your monitor has a manual degauss
button, use it every month or two. The degaussing circuitry in some
monitors has limited power. We have seen monitors that were
accidentally exposed to strong magnetic fields, resulting in a badly
distorted image. Built-in degaussing did little or nothing. In that
case, you can sometimes fix the problem by using a separate
degaussing coil, available at Radio Shack and similar stores for a
few dollars. We have, however, seen monitors that were so badly
"magnet-burned" that even a
standalone degaussing coil could not completely eliminate the
problem. The moral is, keep magnets away from your monitor, including
those in speakers that are not video-shielded.

16.4.2 Troubleshooting Flat-Panel Displays

If
you've tried the basic troubleshooting steps and
your FPD still doesn't work properly, you may have
one or more of the following problems:

If your FPD displays no image at all and you are certain that it is
receiving power and video signals, first adjust the brightness and
contrast settings to higher values. If that doesn't
work, turn off the system and FPD, disconnect the FPD signal cable
from the computer, and turn on the FPD by itself. It should display
some sort of initialization screen, if only perhaps a
"No video signal" message. If
nothing lights up and no message is displayed, contact technical
support for your FPD manufacturer.

Unlike CRTs, where increasing the refresh rate always reduces
flicker, FPDs have an optimal refresh rate that may be lower than the
highest refresh rate supported. For example, a 15-inch FPD operating
in analog mode may support 60 Hz and 75 Hz refresh. Although it
sounds counterintuitive to anyone whose experience has been with
CRTs, reducing the refresh rate from 75 Hz to 60 Hz may improve image
stability. Check the manual to determine the optimum refresh rate for
your FPD, and set your video adapter to use that rate.

First, try setting the optimal refresh rate as described earlier. If
that doesn't solve the problem and you are using an
analog interface, there are several possible causes, most of which
are due to poor synchronization between the video adapter clock and
the display clock, or to phase problems. If your FPD has an
auto-adjust, auto-setup, or auto-synchronize option, try using that
first. If it doesn't, try adjusting the phase and/or
clock settings manually until you have a usable image. If you are
using an extension or longer than standard video cable, try
connecting the standard video cable that was supplied with the
display. Long analog video cables exacerbate sync problems. Also, if
you are using a (KVM) switch, particularly a manual model, try
instead connecting the FPD directly to the video adapter. Many FPDs
are difficult or impossible to synchronize if you use a KVM switch.
If you are unable to achieve proper synchronization, try connecting
the FPD to a different computer. If you are unable to achieve
synchronization on the second computer, the FPD may be defective.
Finally, note that some video adapter models simply
don't function well with some FPD models.

If the screen is displaying a full, stable image, but that image is
of poor quality, first verify that the display is not connected
through a KVM switch or using an extension cable. If it
isn't, connect the display directly to the video
adapter using the standard cable. If that is already the case, adjust
the brightness, contrast, and focus controls. If you are unable to
get a proper image using these controls, the problem is most likely a
clock or phase mismatch, which you can cure by taking the steps
described in the preceding item.

The best way to adjust Clock and Phase is to use auto-adjust first. If this does not solve the problem, go to the Windows Start menu and select Shutdown. When the screen goes gray and the Windows Shutdown dialog appears, leave that dialog on screen, but ignore it. Use the gray screen to adjust Clock and Phase manually. Any problems with Clock and Phase and any changes you make to the Clock and Phase settings are very apparent on the gray screen. Although we have never run an FPD under Linux, our editor wonders if the unadorned X server (no window manager) might serve the same purpose. It displays a crosshatch pattern; if you are at the text console, you can generally start it just by running the command X and exit it with Ctrl-Alt-Backspace. Always adjust Clock first. Clock is usually not a problem if you have used the auto-adjust feature of your monitor, but if you do have Clock problems, they will be evident as large vertical bars on your screen. Tweak the Clock setting until those bars disappear. Then adjust Phase. Phase problems are evident as thin black lines running horizontally across the screen. Adjust Phase until the lines disappear or are minimized. Not all video cards synchronize perfectly with flat panels. The gray Shutdown screen exaggerates the problem, so do not worry if very tiny movements are visible after you've adjusted Clock and Phase as well as possible. After you've set the Clock and Phase controls for the best image possible on the gray screen, cancel the Shutdown and the image should be optimized.

Your video card is supplying a video signal at a bandwidth that is
above or below the ability of your FPD to display. Reset your video
parameters to be within the range supported by the FPD. If necessary,
temporarily connect a different display or start Windows in Safe Mode
and choose standard VGA in order to change video settings.

This generally occurs when you run an FPD at other than its native
resolution. For example, if you have a 15-inch 1024 x 768
FPD but have your display adapter set to 800 x 600, your
FPD will attempt to display those 800 x 600 pixels at full
screen size, which physically corresponds to 1024 x 768
pixels. The extrapolation necessary to fill the screen with the
smaller image results in artifacts such as blocky or poorly rendered
text, jaggy lines, and so on. Either set your video adapter to
display the native resolution of the FPD, or set your FPD to display
the lower-resolution image using less than the entire screen.

This is a characteristic of today's FPDs. Other than
by pure chance, any FPD you buy will have some small number of
defective pixels. Manufacturers set a threshold number below which
they consider the display acceptable. That number varies with the
manufacturer, the model, and the size of the display, but is
typically in the range of five to 10 pixels. Nothing can be done to
fix the problem. The manufacturer will not replace the FPD under
warranty unless the number of defective pixels exceeds the threshold
number. This is simply something you have to learn to live with if
you want to use an FPD.

Again, this is a characteristic of current FPDs. The after-image
occurs when the display has had the same image in one place for a
long time. The after-image may persist even after you turn off the
display. More-expensive models are less prone to this problem than
entry-level models, but all FPDs exhibit the problem to some extent.
It is simply another characteristic of FPDs that you must learn to
live with.

The transistor-based pixels in an FPD respond less quickly than the
phosphors in a CRT. The least-expensive FPDs exhibit this problem
even with relatively slow image movement, as when you drag a window.
Better FPDs handle moderately fast image movement without ghosting,
but exhibit the problem on fast-motion video, such as DVD movies. The
best FPDs can handle even fast-motion video reasonably well, although
no FPD handles it as well as a CRT. The only real solution to this
problem is to upgrade your FPD to a model with faster rise/fall
times. The fastest currently available FPDs have 15 ms rise/fall
times, which are adequate for anything short of 3D gaming.

Use the brightness control to increase image brightness. If you have
set brightness to maximum and the image is still too dim, contact the
display manufacturer. The CCRTs used to backlight the screen have a
finite lifetime and may begin to dim as they near the end of their
life.

One or more of the CCRTs that provide the backlight have failed.
Contact the display manufacturer.

If one or multiple horizontal and/or vertical lines appear on the
display, first power-reset the computer and display. If the lines
persist, run the auto-setup function of your display. If that does
not solve the problem, power down the system and display, remove the
video cable, and verify that the video plugs and jacks on both
computer and display ends do not have broken or bent pins. Even if
all appears correct, try a different video cable. If the problem
persists, contact the display manufacturer.