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NotTaR of Television Sets : Jumping picture on white scenes         
 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.

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Jumping picture on white scenes

This could be an AGC problem if the picture appears overloaded. However, if the picture is normal except unstable, the sync separate is the place to look:

(From: Jack Schidt (jack@wintel.net).)

White screens are a worst case video pattern for sync separators, and will cause an erratic shift in the vertical multivibrator trigger level unless the horizontal and video information is filtered out [integrated] prior to driving the vertical sync input of the processor IC.

This will show up with a scope as high frequency noise going into the vertical sync input.

Look for a small electrolytic [in fact, all of them], around 1-10 uF or so near the deflection/sync processor IC. Often simply increasing the value of this cap will help.