LCD Monitor

Some of the problems related to LCD monitor and their troubleshooting techniques are explained below.

 No image display problemLCD1If 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.

Screen flickers

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 counter intuitive 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.

The screen is very unstable

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.

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 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 phase and clock

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.

“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 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.

Text or lines are shadowed, jaggy, or blocky

This occurs when you run an LCD at other than its native resolution. For example, if you have a 19″ LCD with native 1280×1024 resolution but have your display adapter set to 1024×768, your LCD attempts to display those 1024×768 pixels at full screen size, which physically corresponds to 1280×1024 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.

Some pixels are always on or always off

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.

A persistent after-image exists

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.

Moving images blur, smear, or ghost

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.

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 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