Finally - another item off my TODO list!
My 12v bench power supply is a Watson W-30AM. It's a decent enough PSU, and competitively priced. However, they appear to have a design fault - the fan speed controllers fail... in the "fan off" state.
Mine did so a couple of years ago at a special event station operation, and consequently got rather warm, rather quickly. We performed some quick field surgery and hard wired the fan to +V, which took care of the problem, albeit rather noisily.
This evening I finally made the repair: the LM358 op-amp on the speed control board had let its magic blue smoke out (quite obviously). A quick replacement, along with the rather scorched looking 390 ohm resistor adjacent to it, and it's behaving as it should again. Total cost about £0.50.
I mentioned earlier that I thought it was a design fault: of the four people I'm aware of who have these supplies, three have independently failed in exactly this way...
(As an aside, I'd never buy another linear power supply. They weigh far too much, and leave nice dents in my car's metalwork when you drop them. Decent switch-mode power supplies are smaller, lighter, more efficient, and work every bit as well.)
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