I've got a Denon 5-channel receiver that has a fan on the heatsink. The
fan doesn't run and the unit overheats, unless I short the heatsink fan
test pins -- then the fan runs at low speed and the heat is controlled.

On the heatsink are a couple of temperature sensors that look like
junior-sized TO-220 transistors, except they're grey and have two wires
for legs. The two of them measure differently (resistance vs. heat), but
I don't know which one (if either) is faulty.

How do I test these things, and where do I get replacements? The numbers
on them don't look much like part numbers.

thanks, Isaac