Yamaha R-700 STK3056

I have this old receiver. It plays sometimes then doesn't. It was playing for a bit then it crackled a bit. I wacked the internals a couple of times with a rubber screwdriver handle. It seemed like I knocked out the sound. I have shifted everything around and it doesn't seem to make a difference.
When the protection realy engages by itself, it sounds good. If I close it manually, the right side is crackly unless I turn in up loud. It seems to clear up. With protection relay manually engaged, at low volume I hear faint hum. Would that be capacitors or STK3056?
Thanks