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Old 01-20-2017, 03:05 PM
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old_tv_nut old_tv_nut is offline
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Join Date: Jul 2004
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Substituting an external AGC bias does the trick. When the gain is increased to a point just below overload (which is what the AGC pot should do), there is now enough drive such that turning up the contrast to max and increasing the brightness can drive the high voltage out of regulation.

Now to find what's wrong, which may be a pain requiring pulling the chassis for access. I'll see what resistances I can check in-circuit and while it's still in the cabinet. Checking voltages makes no sense because it's a feedback loop and they normally vary with signal level; in fact, RCA and SAMS disagree, probably depending on exact test conditions.
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