Chris wrote:

>     While I've never opened a switching reg. before, I imagine that the fans
> have their own voltage regulator, they may also me variable speed depending
> on CPU temperature. (My 5000/240 has a t/3/misc/overtemp in the test list)
> It may just be that a 12V regulator or a triac went bad. Assuming one of the
> fans isn't shorted out and/or wired in series of course. Barring those
> symptoms, the fans probably don't need full wave rectified DC, so I bet they
> tap off the 12v AC line before it gets bridged down and filtered. Perhaps a
> rectifier/diode bit the dust; not likely, but possible. Then there's the
> most often not-checked cold solder joints. Just some thoughts.

It is not possible to get a 12v DC output from a 12v AC input.
Rectification occurs before the switching.  Other more crucial components
are likely to be clagged before the fan if the bridge is stuffed.
Could be dry solder joints, but not after all these years.

I would recommend cleaning the dust out of the machine and manually
giving the fans a spin.

	-- Gregory McGarry <g.mcgarry@ieee.org>