atx power supply

Hello I would appreciate it if someone would tell me how to test an atx power supply with digital volt meter. (how to rig the atx plug to turn on the supply so I can check it) Thanks a bunch, flubber

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cm
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I guess it depends how rigorous a test you want to do.

To do it right requires a bunch of high-power adjustable resistors.

To do it at all usually requires at least one substantial load resistor, as most switching power supplies don't run at all with no load.

And you do have to load down all the outputs, as a supply may be able to put out 12 volts with no load, but not with any realistic load.

For very rough starters, get a 1 ohm 50 watt resistor and place it across the 5 volt output, that will draw 25 watts. Or a half-ohm resistor, that's 50 watts. Or more of these in parallel to draw whatever wattage you want to test at.

Same for the 3.3 volt output, only there a one ohm resistor draws about

10 watts.

For the +12 output, a two ohm resistor draws about 70 watts, a one ohmer 144 watts.

For the low-current outputs like -5 and -12, a 10 ohm resistor draws

2,.5 watts and 14.4 watts respectively.

Oh, there's also the always-on outputs, be sure to load them too.

the formula is watts = voltage squared over ohms.

or watts = current squared times ohms.

Go ahead and have fun, just don't burn yourself on the hot resistors!

pins., then ground the remote startup pin for a second, then go ahead and measure the voltages.

Reply to
Ancient_Hacker

Thank you, you've helped a bunch. I had forgotten about the remote startup... thanks again

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Reply to
cm

On the atx connector theres a green wire. take a paperclip or small piece of wire, push it into the hole of the green wire, and then to any of the black wires. the unit will turn on. you can check the voltages, remember, yellow wires should be +12v red +5v and I believe orange is -5v. but. to properly test a ATX supply, you should get a ATX tester. it can test it for you. and without any load on the ps, it will be hard to diagnose any voltage problems. by itself the voltages might look fine but when actually under load, they can be way off. when ti is under load it should still be within the tolerance for + and - if it isnt then its time to replace it. if the voltages are under while running the hardware normally, you could do damage to it. same if they are over beyond tolerance.

ive lost a hard drive due to a faulty PS over voltage damaging the drive. so better to be safe than sorry. maybe someone else here has alot more experience with testing them to be able to offer other suggestions. :)

Reply to
Heavy G

cm wrote in news:4538dc0c$0$19694$ snipped-for-privacy@free.teranews.com:

So you load down the outputs and turn on the ps and measure the voltages. If one of the voltages is off, you'll know the ps is bad. But what if all the voltages are within spec? Can you conclude that the ps is OK? No, you can't! Because all the voltages may be OK for hours, then one of them has a glitch. Your PC may not run well under those conditions. And you may never see it, even if you stare at your voltmeter for hours. Conclusion: substitute a known-good ps. (Power supplies are cheap.) If your PC problems go away, be happy.

Reply to
Jim Land

You did not happen to read thsi group's FAQ?

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Sam Goldwasser a web page -- Troubleshooting and Repair of Small Switchmode Power Supplies. A little education is always useful. Also remember that switch mode power supplies -- have high voltage ( > 300 volts) inside - that is part of the design!

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gb

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w9gb

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