I usually repair guitar amplifiers. But I've been getting into repairing vintage receivers and other devises. I'm self taught and have been doing pretty good so far. I just repaired a Harman Kardon PM660. Well, repaired it for the most part. I had to replace a couple output transistors, a driver transistor and a couple 1/4 watt resistors. It's out in my shop playing right now and sounds great. But sometimes you turn it on and it doesn't work. I get a periodic pop like a breaker is kicking on and off. I play with it a bit and turned it off, let it sit a minute and it started working again. And as I said it's sounds fine. Been playing for about 20 minutes now.
Anyone have any ideas what might be causing this problem? I don't want to give it back to the owner and have this happen to him. The speaker impedance is correct. Thanks in advance.