Chapter 3 - Troubleshooting
Video Failures
Problems that develop in the video circuits can appear as subtle or major distortions, a loss of one or more colors, improper video level, or a complete loss of video. When troubleshooting LCD display devices the problem must be isolated to 3 major components: The main board where the video processing is performed, the TCON board, or the LCD panel. In some cases the TCON may not be available as a separate component and replacement of the LCD panel is required to rectify a TCON problem.
Distortion in the video signal that affects all inputs can be challenging at times since any of the above mentioned components can cause this. Fortunately, each of these components tends to generate unique symptoms when a problem occurs. Some distortions may occur that could be caused by either of these components but a good understanding of the circuits and further investigation will isolate the suspected circuit. The following sections will cover the various scenarios of problems that may occur in the video processing circuits.
No Video
A “no video” complaint can be caused by a number of reasons. The first step is to determine if the condition is present from all input sources. If any video source is working properly, the TCON can be assumed to be OK. The backlights are also functioning properly. Although it is unusual for a backlight failure to cause a complete loss of video (the unit will shut down if a backlight power or open LED is detected) there have been cases where the backlights have failed to turn on without the unit shutting down.
If the loss of video occurs on all inputs, the problem will require additional diagnostic work. The presence of audio is an important sign to check for. Missing audio accompanying a loss of video helps to eliminate the TCON as the cause and would point to the BAL board as the culprit. If audio is present, the next step is to determine if the video loss is occurring in the video process circuits on the BAL board or the LVDS cable link from the BAL board to the TCON, or the TCON itself.
Service Tip: If a service call is made for a “no video” complaint, a warranty repair would require the technician to bring a BAL board to the location. The technician will install the board (hopefully the correct one) and if the video problem is not remedied, it is safe to assume the problem might reside in the TCON.
One method to test a TCON, which works rather well in most cases, is to remove the LVDS connector at the LCD panel (the TCON board is internal to this panel) while the unit is running. Be certain to release the lock tabs and handle the connector carefully to avoid damage.
Carefully insert and remove the connector while slightly rocking it. Observe the screen as you do this. If any activity appears on the screen (flashes, lines or patterns) The TCON is OK. The unit may shut down within a 10 to 20 second period because the protect circuits have detected a TCON failure. If this happens, simply
The troubleshooting flowchart in Figure
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