Display Troubleshooting

Troubleshooting CRTs versus LCDs 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 step you take depends on the type of display. The following sections cover basic troubleshooting for CRTs and LCDs.

CRTs seldom fail outright without obvious signs, such as a loud snap or a strong odor of burning electrical components. Most CRT problems are really problems with the power, video adapter, cable, or hardware/software settings. To eliminate the CRT as a possible cause, connect the suspect CRT to a known-good system, or connect a known-good display to the suspect system. It is worth noting, that older CRTs eventually wear out, and starts dimming. Common signs of a weak CRT are a dim picture, dysfunctional brightness and/or color controls, image smearing at high brightness, and in color CRTs, a tint towards a single color (Red Green Blue)

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

Even if the CRT is in warranty, the shipping costs may exceed the value of the CRT. For example, shipping a CRT both ways can easily cost $75 or more. If that CRT is a year-old 17" model, you're probably better off spending $100 to $200 for a new 17" or 19" CRT than paying $75 in shipping to have the old one repaired. CRTs 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.

DON'T MESS WITH CRTs

Never disassemble a CRT. At best, you may destroy the CRT. At worst, it may destroy you. Like televisions, CRTs use extremely high voltages internally, and have large capacitors that store that energy for days or even weeks after the CRT 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 CRTs and televisions for a living treat them with great respect, and so should you. If you must repair a CRT, take it to someone who knows what they are doing. You have been warned.

Here are some common CRT problems:

Check the obvious things first. Verify that the CRT is plugged in (and that the receptacle has power), the video cable is connected to the video card, the computer and CRT 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 CRT, video card, or video cable may be bad. Check the suspect CRT on a known-good system or a known-good CRT on the problem system.

CRTs contain multiple filaments, which can be broken, or gas may have leaked into the vacuum inside the CRT. CRTs damaged this way are unrepairable without specialist equipment. With the display open. check if all three filaments are glowing bright orange. Excessive redness or purple arcing signifies gas has leaked in. There may also be an internal short inside the CRT, which is also unfixable without specialist equipment.

POWER MISMANAGEMENT

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 CRT. To verify this problem, turn off power to the system and CRT and then turn them back on. If the CRT then displays an image, check the power management settings in your BIOS and operating system and disable them if necessary.

The horizontal and/or vertical deflection system has failed. The CRT tube itself is fine, but the circuitry driving the tube has failed. Replace the display.

This is a hardware problem with one of the electron guns. Replace the CRT. This problem may also manifest as a strong color cast during normal operation that is not correctable using the normal color balance controls.

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

There are two likely causes. First, you may be driving the CRT beyond its design limits. Some CRTs 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 CRT is shortened dramatically, perhaps to minutes. To correct this problem, change video settings to values that are within the CRT's design specifications. Second, the power receptacle may be supplying voltage lower than the CRT requires. To correct this problem, connect the CRT 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 CRT 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 CRT 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.

In elderly systems, 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. Remove the DVD decoder card. If your video adapter includes hardware DVD support, or if you are upgrading to such an adapter, you don't need a DVD decoder card.

This is also a symptom of a weak CRT, in which case the display should be replaced.

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

The horizontal or vertical deflection system may also have failed, in which case the display should be replaced.

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 CRT. 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 CRT, particularly if you have just installed the CRT or have just changed video settings. To verify this, restart the system in Safe Mode (press F8 during boot to display the Windows boot menu and choose Safe Mode). If the system displays a VGA image properly, change your display settings to something supported by the CRT.

The horizontal or vertical deflection system may also have failed, in which case the display should be replaced.

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

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

The horizontal or vertical deflection system may also have failed, in which case the display should be replaced.

In older television sets (aka roundies, in which the CRT has a round face), this may be normal behavior.

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 three feet from the CRT. Note that such interference can sometimes penetrate typical residential and office walls, so if the CRT 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 CRT into a surge protector. Better still, plug it into a UPS or power conditioner that supplies clean power at a constant voltage.

This problem may also be caused by using a video cable that is too long or of poor quality or by using a poor-quality KVM switch (keyboard/video/mouse switch). Manual KVM switches are particularly problematic.

The horizontal or vertical deflection system may also have failed, in which case the display should be replaced.

The filaments may be receiving inadequate power, in which case all transformer windings, resistors and electrolytic capacitors should be checked.

The CRT may need to be degaussed. A CRT 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 CRT to a strong magnetic field, such as unshielded speakers, can cause more extreme image problems. Many modern CRTs degauss themselves automatically each time you cycle the power, but some have a manual degauss button that you must remember to use. If your CRT has a manual degauss button, use it every month or two. The degaussing circuitry in some CRTs has limited power. We have seen CRTs 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 RadioShack and similar stores for a few dollars. We have, however, seen CRTs that were so badly "magnet burned" that even a standalone degaussing coil could not completely eliminate the problem. The moral is to keep magnets away from your CRT, including those in speakers that are not video-shielded.

The horizontal or vertical deflection system may also have failed, in which case the display should be replaced.

An incorrect yoke may have been attached to the CRT. Unless you have a lot of spare time on your hands, this is usually not worth fixing. Replace the display.

You may have a weak picture tube. Without specialist equipment, this is usually unfixable. You could try a CRT rejuvenator as a last resort, but this may fix or kill your CRT permanently.

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

If your LCD displays no image at all and you are certain that it is receiving power and video signal, first adjust the brightness and contrast settings to higher values. If that doesn't work, turn off the system and LCD, disconnect the LCD signal cable from the computer, and turn on the LCD 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 LCD manufacturer. If your LCD supports multiple inputs, you may need to press a button to cycle through the inputs and set it to the correct one.

Unlike CRTs, where increasing the refresh rate always reduces flicker, LCDs have an optimal refresh rate that may be lower than the highest refresh rate supported. For example, a 17" LCD 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 LCD, and set your video adapter to use that rate.

First, try setting the optimal refresh rate as described above. 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 LCD has an auto-adjust, auto-setup, or auto-synchronize option, try using that first. If not, 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 LCD directly to the video adapter. Many LCDs are difficult or impossible to synchronize if you use a KVM switch. If you are unable to achieve proper synchronization, try connecting the LCD to a different computer. If you are unable to achieve synchronization on the second computer, the LCD may be defective. Finally, note that some models of video adapter simply don't function well with some models of LCD.

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 so, 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.

ADJUSTING CLOCK AND PHASE

The best way to adjust clock and phase is to use auto-adjust first. Check the utility and driver CD that came with the monitor. It may have a wizard or at least the appropriate background screens to use while adjusting phase and clock settings. If not, go to the Windows Start menu and select Shutdown. When the screen goes gray and the Windows Shutdown dialog appears, leave that dialog onscreen, 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 clearly evident on the gray screen.

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 analog video cards synchronize perfectly with flat panels. The gray Shutdown screen exaggerates the problem, so don't 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 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 LCD to display. Reset your video parameters to be within the range supported by the LCD. If necessary, temporarily connect a different display or start Windows in Safe Mode and choose standard VGA in order to change video settings.

This occurs when you run an LCD at other than its native resolution. For example, if you have a 19" LCD with native 1280x1024 resolution but have your display adapter set to 1024x768, your LCD attempts to display those 1024x768 pixels at full screen size, which physically corresponds to 1280x1024 pixels. The pixel extrapolation needed 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 LCD, or set your LCD to display the lower-resolution image without stretching the display (a feature sometimes referred to as display expansion), so that pixels are displayed 1:1, which results in the lower resolution using less than the entire screen.

This is a characteristic of LCDs, particularly older and inexpensive models, caused by defective pixels. Manufacturers set a threshold number below which they consider a display acceptable. That number varies with the manufacturer, the model, and the size of the display, but is typically in the range of 5 to 10 pixels. (Better LCDs nowadays usually have zero dead pixels.) Nothing can be done to fix defective pixels. Manufacturers will not replace LCDs under warranty unless the number of defective pixels exceeds the threshold number.

Advice from Ron Morse

Some people claim that leaving the unit powered off for a day or two will "erase" a persistent after-image. Others suggest leaving a neutral gray screen (like the one used for phase adjustment) up on the screen to "equalize" the display. I dunno. FWIW, I've seen this problem on older Samsung panels but never on the Sony or NEC/LaCie panels I use.

Again, this is a characteristic of LCDs, particularly older and inexpensive models. 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 the display off.

Transistor-based pixels in an LCD respond more slowly than the phosphors in a CRT. The least-expensive LCDs exhibit this problem even with slow image movement, as when you drag a window. Better LCDs handle moderately fast image movement without ghosting, but exhibit the problem on fast-motion video. The best LCDs handle even fast-motion video and 3D gaming very well. The only solution to this problem is to upgrade to an LCD with faster response time.

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 more 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 the system and display down, 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.

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