SX-1250 Main Outputs Fail

If you can't test it reliably on a meter, how do you know if the STV has failed? How difficult is it to make the replacements you reference?

You can test them, with you meter in the diode test setting, if your meter wont respond to measuring one, then you most definitely need a better meter, especially if you are working at this level.

I have never seen a STV3 go bad in the 20 odd years I have been doing this. This includes whole power amps which have completely detonated and fried themselves.

Assumption is the mother of all F ups....

I just measured one with my Fluke 115, they are 1.47V
 
Thought I'd adequately checked the left amp by removing all the transistors and diodes and testing them off board. Not exactly sure where to go from there, once I've got new trimpots installed.



If you can't test it reliably on a meter, how do you know if the STV has failed? How difficult is it to make the replacements you reference?

Did you test all the reststers?

My experience was a whacky STV would fail under power. I suppose you could sit on the system with meters and scopes and such to watch it run wild. I had tested everything else and when all else fails to expose a problem, you start to guess and swap parts. Having known good parts to try is one way. Making parts is another way. Side to side swapping is a method. It you can disable the good side and barrow parts, that’s a method.

Sometimes fixing old electronics is a bitch.

The other SOB is hairline cracks in the traces. Everything tests OK but the bastard doesn’t work.

Did I mention that sometimes fixing electronics is a bitch?

Oh, and intermittent problems, those are a bitch too.

Sometimes trying to tell someone how to fix electronics by an online thread can be painful.
 
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