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:

Monitor displays no image

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.

Monitor displays only a thin horizontal line or a pinpoint at the center

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.

Monitor flashes one color intermittently, even when the screen is blanked

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.

Monitor snaps, crackles, or pops when powered up, or emits a strong electrical odor

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.

Monitor emits a very high-pitched squeal

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.

Monitor displays some colors incorrectly or not at all

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.

Image rolls or a horizontal line scrolls constantly down the screen

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.

Image flickers

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.

Image is scrambled

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.

Image displays rectilinearly, but is incorrectly sized or aligned on screen

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.

Image displays other than rectilinearly (trapezoid, parallelogram, barrel, or pincushion)

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.

Image wavers or shimmers periodically or constantly

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.

Colors are "off" or smearing appears in some areas

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:

No image

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.

Screen flickers

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.

The screen is very unstable

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.

Poor image

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.

Signal out of range message

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.

Text or lines are shadowed or blocky

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.

Some pixels are always on or always off

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.

A persistent after-image exists

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.

Moving images blur, smear, or ghost

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.

Dim image

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.

Image is only partially backlit

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

Horizontal or vertical lines appear

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.