The temperature sensor that activates the fan nearly always goes bad in a few years.
If it makes the fan run all the time, you'll wear out the fan's sleeve bearings. If you're lucky it will get loud and warn you before it seizes up and the radio blows up from overheating.
And if the failed temp sensor prevents the fan from running at all, this just breaks the radio faster.
We adopted a fix that patches the temp-sensor circuit to the built-in amplifier's keying relay. When the mike is keyed, the fan runs, and shuts off when receiving.
More reliable than trying to make the temp sensor work like it should.
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