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In How to test a power supply, the answers focus on testing ATX power supplies.

I have a pre-ATX power supply. How do I ...

  • Safely test that the extracted old PSU is not producing expected voltage?
  • Safely test the replacement PSU is producing good voltage before installing it?

By safely I mean with minimal risk to PSU and with no risk to server's motherboard etc from this preliminary test. I'm looking for a minimal test for reassurance / quick check, not full-load testing.

Generic answers are probably more useful for other people but, in case it helps, the details of this are:

It is for an Intel Pentium II server.
It is a 325W PSU.
The connectors are mostly conventional but it is proprietary (Compaq Proliant 1600)

PSU PSU

The long lead goes to a front-panel "power on" LED and to a latching on/off switch. I can extract the switch and connect it to the end of the long lead for testing).

I have multimeters and can rustle up small test loads (fans, 10 W 10-20 Ω power resistors, etc)

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  • Are you asking how to test under a heavy load?
    – Keltari
    Commented Jun 15, 2021 at 17:54
  • @keltari, no, just whatever is needed for the PSU to turn on so that 12V and 5V outputs can be checked with a voltmeter. I just want to 1) test the old PSU appears truly dead (and there's not a problem else where). 2) basic check of replacement PSU before attaching it to server. I'll update question to clarify.
    – RedGrittyBrick
    Commented Jun 15, 2021 at 17:57
  • Well, that PSU was connected to a motherboard, so you should be able to identify the on/off switch part (or, as you wrote, just connect that to the switch again). That should allow you to test voltages, unless your PSU requires an actual load to produce voltages (some rare custom PSUs do, though I am not sure if that ever applied to IBM PC PSUs). In that case, you need suitable resistors to simulate the load. Or in other words, that bridge for the ATX PSU that simulates the switch is at your "long end", if that is the question.
    – dirkt
    Commented Jun 15, 2021 at 19:48
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    Many power supplies require a minimum load or they shut down. You might need to use some resistors or 12 volt and 6 volt (close enough) auto lamps as load.
    – DrMoishe Pippik
    Commented Jun 15, 2021 at 21:45

1 Answer 1

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I believe this is an AT (not ATX) PSU with switching at the PSU. These (photo) are the leads for the power supply switch. You can connect them to a properly rated switch or jumper them but, if I remember correctly, this is a Double Pole Latching Switch for mains level voltage, so (this is not a joke) try to not kill yourself.

enter image description here

This differs from the newer ATX scheme which uses a low voltage momentary signaling which requests that the motherboard shutdown (press to power on/off; hold for 4 secs to force shutdown)

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  • After the OP did not kill himself with the switch, can he simply use a multimeter to check voltages on the pins?
    – Dercsár
    Commented Oct 4, 2023 at 14:31

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