NotTaR of Television Sets : Jumping picture on white scenes         
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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.