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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Posted to sci.electronics.basics,sci.electronics.repair,alt.comp.hardware.pc-homebuilt
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What does the missing thermistor do? (PC power supply)
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 datasheet at http://www.ortodoxism.ro/datasheets/...ild/KA3511.pdf pin 18 is the Extra Protection (EP) input, which, when its voltage goes high enough, is supposed to shut down the PSU. In other words, this seems to rule out the thermistor being used as a overheat sensor because the 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 This thermistor is not for fan speed control -- that's handled by another thermistor (next to the screw on the heatsink, higher up in the picture). |
#2
Posted to sci.electronics.basics,sci.electronics.repair,alt.comp.hardware.pc-homebuilt
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What does the missing thermistor do? (PC power supply)
On 7 Jan 2006 19:52:47 -0800, "larry moe 'n curly"
put finger to keyboard and composed: 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 datasheet at http://www.ortodoxism.ro/datasheets/...ild/KA3511.pdf pin 18 is the Extra Protection (EP) input, which, when its voltage goes high enough, is supposed to shut down the PSU. In other words, this seems to rule out the thermistor being used as a overheat sensor because the 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 This thermistor is not for fan speed control -- that's handled by another thermistor (next to the screw on the heatsink, higher up in the picture). I suspect the PT (extra protection) input may be a current sensing input. I don't understand the purpose of the thermistor, though, unless it is there to derate the PSU at higher temperatures. - Franc Zabkar -- Please remove one 'i' from my address when replying by email. |
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