Support for a Quested D1500M amplifier - fan control and bias module

Good day friends

A mate of mine has a Quested D1500M power amplifier (made by Hill Audio in the UK in the 80s). This amplifier module has an interesting history where it ended up in plenty of large recording studios around the world.

The actual amplifier is working very well. My friend attempted to replace the fan driver opamp and unfortunately created a short-circuit. A couple of parts and devices blew on the module when he powered it up.

Now we are on the prowl for a service schematic. We were in touch with Hill Audio but with not much luck.

The fan controller is not much of a worry - but the bias relay control is. Does anyone have an idea how the bias relays engage with the amplifier channels? It seems they slack off the bias when the temperature goes beyond a preset point.