M-70 Needs Help

 
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+P should be a positive 79v. Like pete is trying to get at. Your missing the +79 v rail. And open diode in the bridged rectifier (D701), or a cold solder connection(D701/704), burnt or cracked trace on the circuit board, or D704 is open.

Or... Something down stream is loading down the +79v rail.. ( I would think this would cause something to get pretty damn smok'n hot.)
 
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Well we are good to go...thanks guys! I'm glad I decided to re tackle this one.

Turns out I should have done a better job of getting rid of all the glue and unbeknownst to me it had more electrolytic gunk mixed in which ended up being pretty corrosive. Just in this short period of time the new IN4004 that I had put in d704 a couple of months ago was heavily corroded from the residue. This area is hard to inspect with the board installed so I couldn't see that until I disassembled it again.

So after a thorough surface cleaning I replaced all of the diodes and resistors that I had previously replaced and we are now good to go. Offset and bias dial in just right and it sounds excellent.

Now I just have to remember how to put it back together:D

Ahh...should have not moved off of this unit until it was fixed!

Thanks again guys
 
Yep once I started taking voltage readings it became pretty obvious that's where the problem was at...good call
 
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