CRT Monitor

17-Inch-CRT-Monitor-CMS1703F-             CRT TUBE

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.

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.

One thing to bear in mind is that if your CRT runs into a problem don’t ever try to dissemble it. lAt best, you may destroy the CRT and at the 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. 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 she is doing. You have been warned. Some of the common CRT monitor related problems are given below.

CRT displays no image

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.


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.

CRT 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.  At this case you have to replace th CRT monitor.

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

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.

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

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.

CRT emits a very high-pitched squeal

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.

CRT 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 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.

Image rolls or a horizontal line scrolls constantly down the screen

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.

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 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.

Image is scrambled

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.

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

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.

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

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.

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 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.

Colors are “off” or smearing appears in some areas

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.