Quote:
Originally Posted by N2IXK
It is really difficult to follow what is going on with the schematic incomplete and in a different thread.
Can you post a bigger chunk, so we see where the ABL signal from the pot wiper goes? Somewhere into the video amps, I assume.
Scope the B+ voltage that feeds the video amps, and look for ripple/ringing there.
Check the zener diode using the diode check on a DMM as a first go. That will conclusively check for opens/shorts. I'm betting it is still good though. Im thinking you might have a bad bypass cap in the video amp somewhere.
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The wiper goes directly to the base of the ABL transistor. From there it leaves the collector, through the contrast control and then on to the base of the base of the third video amp.
I'll do the B+ tomorrow. The DMM will tell me if the diode is working as far as passing in one direction. Wouldn't I need to supply 7.5V to open for testing in the other direction? Would a 9V battery do the trick?
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Last edited by TinCanAlley; 09-28-2013 at 12:39 AM.
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