SWR SM-900 bass amp - fan circuit problem

[Tone Meister]

SWR-era SM-900 bass amp, the fan unit works fine when I apply direct voltage from my power supply, but the fan doesn't come on during operation. I really have no idea where to start, so I'm hoping you fellas can help me sort it out for my buddy.

Schematic attached.

[Enzo]

So there is a thermal switch in series with the fan motor. Hit that with a heat gun and see if it turns on.

[Tone Meister]

Yes it did.

[Enzo]

OK then, the fan circuit is working. When the amp gets hot enough, the fan will come on.

[Tone Meister]

Best "repair" yet. Buddy complained that fan never comes on, which is probably a good thing. Thanks Enzo.