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Sherwood S-7900A - Repair and restoration

Thanks Rick. I measured -9.2v at base of Q903 (should be 0v) and full rail voltage at the other side of R922. I pulled the bias transistor Q904 and it measured a bit suspicious. Luckily I had a TTA004B on hand and put it in. The Q903 base went to 0v and the right speaker output went from -43vdc to 2mv. Looks and sounds good now. I recapped both boards but found I couldn't get the bias to move (L@40mv and R@2mv). I'm going to order a few more parts to recap the power supply and main filters. Probably do the driver board transistors and bias adjust pot. I'm very happy with this S-7900a and am excited to get it closer to optimum operation.
 
Happy to hear Q904 was the problem. Comparing measured voltages with schematic can really narrow down the problem.
 
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