NotTaR of Television Sets : Disappearing Red (or other color)       
 Copyright © 1994-2007, Samuel M. Goldwasser. All Rights Reserved. Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: 1. This notice is included in its entirety at the beginning. 2. There is no charge except to cover the costs of copying. I may be contacted via the Sci.Electronics.Repair FAQ (www.repairfaq.org) Email Links Page.

     << Color TV only displays on.. |  Index  | The wandering black blob .. >>

Disappearing Red (or other color)

Problem: I have been given an old colour TV. The reception is good, but very often, when the contrast and brightness of the TV image is low (e.g. when a night scene is shown), the red colour slowly disappears, leaving behind the green and blue image and many red lines.

The remaining red retrace are the giveaway that this is most likely not a CRT problem.

(If there were no red lines, it could be the filament for the red gun of the CRT going on and off due to a bad connection inside the CRT - bad news.)

How is a black and white picture? (Turn down the color control).

If B/W picture is good, then the problem is somewhere back in the chroma decoder circuitry.

Check the video input to the CRT video driver board and signals on that board. If B/W picture is also bad, then you can compare red and green signals to determine where they are becoming different. The red lines in your description sounds like the red video output circuit is drifting and messing up the background level, blanking, screen, or other setting. Could be a capacitor or other component.