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Power Supply tests good, but won't power up system
I have a small form Optiplex GX-520 (power supply - Dell p/n: N8368). It will not power on - now and then I get the infamous orange power light indicating a bad power supply. However, when I connect it to my power supply tester, it turns on, the fan works, all voltages and the "power good" signal are well within normal operating parameters. If I connect a different power supply to the computer, it fires right up, so the system itself is fine. It just doesn't like this particular power supply. Since the "faulty" power supply has the larger motherboard connector, I don't currently have a PC in my shop that it will plug into to check if it's fine with a different motherboard.
It's left me curious. What could be wrong with a power supply such that it fires right up and passes all tests when on a tester, but does not make the GX-520 motherboard happy?
Thanks,
Lonnie Borntreger
fireberd
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February 12th, 2009 15:00
A tester that will test a power supply under load is probably available but probably a high $$ item the power supply manufacturers and maybe PC builders have. It would require some high power resistive loads, considering the amperage that the various voltages will handle. You would have to set it up for each power supply, e.g. if the +5V is rated at 20 amps you would need a tester that would provide that load (P=IXE and in this case it would need a 100 watt load). If you had a power supply with a +5V that was rated at 30 amps you would need a 150 watt load. You would need similar loads for a the various voltages.
fireberd
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February 12th, 2009 04:00
The tester you have is apparently not testing the power supply under "load". With the apparent no load, the power supply is OK but when connected and the PC is drawing current from the power supply one of the voltages is failing. And, since another power supply works with the PC it also says the power supply is bad.
lonnieborntrege
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February 12th, 2009 12:00
Where would I find a tester that tests under load? Sounds like something I need to add to my toolbox.