The thermal protection circuit is activating before the 60 degree centigrade
fan switch is cutting in, under high load.
The fan switch temperature , testing in isolation , is about right.
I'd rather change the switch to a 40 degree one rather than tracing the
drift in the thermal protection circuit.
Any advice? or even if there is a recognised cure in the thermal matching
circuit ,eg replacing/matching Vbe of the sense transistors.

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Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
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