Yamaha PC2002M Thermal Protection Circuit

[PJC58-Hythe]

Please move if this post is in the wrong place.

This is for anyone who has to work on a Yamaha PC2002M and finds out that the thermal protection bolted to the heatsinks is not simply a thermal switch as detailed in all the service data. I assume this was a later modification which uses 2 x thermal switches and an SR (Set Reset) logic circuit, which not only drives the thermal LED indicator but also switches in the output protection IC and releases the output relays. The protection IC's, IC301 & 401, normally have pin 3 taken to ground but in this model it is connected to the thermal protection circuit. I have attached a PDF showing the circuit (which I had to trace out) and a picture of the PCB with one of the thermal switches removed. I hope this prevents someone else wasting time trying to find a service manual with this circuit in!