stevem Messages: 4738 Registered: June 2004 Location: NY
Senior Member
Take a good close look at the two rectangular 5 watt resistors mounted near each square metal heat sinked cased drive transistor on the output board.
You may need to unsolder one end to see the non lettered bottom, but if that bottom side shows any signs of cracking then replace it as it may be going intermitantly open on you.
If you replace any then steep up to a 7 watt version if you can.
Also note that the any other small metal cased transistor needs to be looked at close too, as back then there leads tended to snap off at the bottom of the transistor if the factory instlled them bent up.