Rick S. wrote:


"larry moe 'n curly" wrote in message oups.com...

I have some 350W Fortron-Sparkle model FSP-350BU PSUs with empty spots
where a thermistor and fixed resistor would normally be connected in
series, and I'd like to know their purpose. I think that they connect
this way:

http://static.flickr.com/39/83308555_59e5e557a6_o.jpg

Capacitor C10 and pin 18 are on the small vertical circuit board
(beneath the removed fan controller board in the photo below) housing
the Fairchild KA3511DS PSU controller chip, and according to the
URL=http://www.ortodoxism.ro/datasheets/fairchild/KA3511.pdf]Data sheet
for KA3511DS[/url], pin 18 is the Extra Protection (EP) input, which is
supposed to shut down the PSU if its voltage goes high. In other
words, this seems to rule out the thermistor being used as an overheat
sensor because pin 18 is low anyway in normal operation.

Here are where the missing resistor and thermistor are located (circled in red):

http://static.flickr.com/39/83310554_91d773cf62.jpg

The missing thermistor has nothing to do with controlling the speed of
the fan, and there's another thermistor for that purpose anyway (on the
heatsink, just above the screw).

Just a guess, but some FSP supplies have dual fans (front and
rear, or bottom and rear). Maybe the "missing" thermistor and
resistor and for a second fan?

I'm sure it doesn't because it connects through an adjustment for the
PSU's output voltage, and the circuit board has no place to connect a
second fan (and I'm counting even the unmarked empty holes). The small
circuit board on the right side of the photo is the fan controller.

Antecs also have a second thermistor (installed) that's unrelated to
fan control, but nothing happened when I connected a variable resistor
across it and took the resistance way down.