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How to Test a Power Supply with 3 Pin Fan Header?

gdea73gdea73
edited December 2011 in Hardware
Slightly related to my other question, but I would find this useful as I have several old PSUs I would like to test.

(Okay, first step is to get a multimeter, which I haven't done yet, but I will soon. And when I get it I need to be sure I can actually test PSUs this old/strange.)

So the kind of power supplies I'm dealing with are Gateway ATX oens with fans on the side to cool the CPU, also there's a plastic fan duct to direct the air over the CPU. These PSUs have no switch on the back, and have a 3 pin fan header. Yes, a fan header coming from the PSU. Whoever came up with this wiring, thank you *so* much.

So if I'm testing this PSU without having it connected to a motherboard, how will I make sure the fan's running? The PSU needs to receive *its own power* to power its own fan, and I guess it couldn't have done that internally.

Is there any way around this, other than testing without a fan? (Do I really have to get out a test board, with a different PSU which doesn't have a fan header, and plug in the fan header to a separate motherboard?)

Thanks, this would help me a lot, as I've got 3 power supplies I need to test/eliminate, and likely more soon.

Comments

  • gdea73gdea73
    (i.e., could I use an adapter to connect the 3-pin fan header back into a molex plug? lol, this is ridiculous, but would that work?)
  • noonenoone
    You can convert a molex to a 3pin fan header connection, but not vice versa. The 3 pin fan connector drops the 5V connection from the molex plug and its common and replaces that with a sensor connector if i recall (if it supports it, otherwise the 3rd pin is just there to be useless).
    If you're testing for the voltage from the fan connector with a multimeter, it should read around 12V.
  • gdea73gdea73
    Thanks for the response... but I'm not sure you understood what I'm asking...

    I'm not trying to test the fan connector itself—I'm merely attempting to test the Molex connector voltage and the 20/24 pin connector for the motherboard. I don't care about the fan header, except for the fact that I need the fan to run while testing the PSU.

    So my question was how to accommodate the fan header when testing the PSU. Obviously it won't be attached to the motherboard, when testing the motherboard connector, so I am guessing I'll have to use an extra motherboard & extra PSU so that I can power the PSU's fan while testing it.

    Does this make sense at all? If it doesn't please tell me, and I can try to elaborate further.
  • noonenoone
    GDEA73 wrote:
    Thanks for the response... but I'm not sure you understood what I'm asking...

    I'm not trying to test the fan connector itself—I'm merely attempting to test the Molex connector voltage and the 20/24 pin connector for the motherboard. I don't care about the fan header, except for the fact that I need the fan to run while testing the PSU.

    So my question was how to accommodate the fan header when testing the PSU. Obviously it won't be attached to the motherboard, when testing the motherboard connector, so I am guessing I'll have to use an extra motherboard & extra PSU so that I can power the PSU's fan while testing it.

    Does this make sense at all? If it doesn't please tell me, and I can try to elaborate further.
    Not really. I'm reading this as you wanted to test the power supplies without using a motherboard and running a fan. If that was the case, the power supply *should* be able to turn on by shorting pin 16 (the green wire going into the motherboard plug) to ground. (I don't think it matters which ground pin, any of the black wires). Keep that grounded until you want to turn the PSU off. I can experiment with this tomorrow afternoon with some equipment I have to double check.
  • BlueSunBlueSun
    My understanding of this is that the fan inside the PSU is being powered / controlled by the motherboard.

    In that case, all you need is an adapter to go from the 4 pin molex to the 3 pin header the fan needs. If you don't have one, you can rig one up fairly easily if you have some scrap wire.
    noone wrote:
    the power supply *should* be able to turn on by shorting pin 16 (the green wire going into the motherboard plug) to ground. (I don't think it matters which ground pin, any of the black wires).

    It doesn't matter which ground you choose, they're all the same. Kind of the point of "ground" :P
  • noonenoone
    BlueSun wrote:
    noone wrote:
    the power supply *should* be able to turn on by shorting pin 16 (the green wire going into the motherboard plug) to ground. (I don't think it matters which ground pin, any of the black wires).

    It doesn't matter which ground you choose, they're all the same. Kind of the point of "ground" :P
    If it's made by morons, sometimes it does because I remember one power supply I had used a ground that wasn't in common with the others. Screwed a lot of stuff up. Ended up getting returned.
  • gdea73gdea73
    haha true... well if I never quite made my point here, the title was misleading, it should've been How to test a Power Supply which has a 3 pin fan header.

    I really don't get the point of powering the PSU fan through the motherboard (which is, powered by the PSU). Ah well, I guess either I'll get/make an adapter to plug the wire back into the PSU (lol), or just use a spare MB & PSU for the sake of testing. If I need to test more, I guess that's what I'll do.
  • DuffDuff
    How many wires are going to the connector? If it's just one that's for the motherboard's fan RPM sensor, not powering the fan, and plugging it in isn't necessary for testing.
  • gdea73gdea73
    Two. Purple and black. I'm fairly sure that it doesn't run when unplugged.

    I am sort of confused, actually, because I plugged it in to a power supply tester I bought, but the thing only lit up for a second or two and then turned off.

    It's an old Gateway PSU, and it does turn on when connected to a motherboard, but has no switch on the back and as such won't stay on if I connect it to the PSU tester.

    What now? I was thinking about buying a multimeter, but I want to use this PSU tester if I can.
  • gdea73gdea73
    Yes, I was wrong! (:P)

    Fan runs when not plugged in to motherboard - that solved some problems, haha. Don't know why it had 2 wires though.

    Also, I was being a tard, the PSU actually is dead. Tested a different one and it did stay on, though it's beeping at me. So I guess I need some new old PSUs, lol.

    Thanks for the help.
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