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testing computer power supplies

Discussion in 'Electronic Repair' started by Bart Bervoets, Jun 29, 2006.

  1. Is it bad for a computer power supply to be switched on without a load?
    I know it's possible to start the power supply, i get loads of power
    supplies in
    from returns but i don't want to chance blowing a mainboard up
    (i could hook an old cd rom drive up to put a load on 5 and 12v but
    would like to avoid clutter.)

    Bart Bervoets
  2. AZ Nomad

    AZ Nomad Guest

    Put a bunch of power resistors in a switchbox. I used an old power
    supply and kept its fan for cooling the resistors.
  3. junebug

    junebug Guest

    Just use an old hard drive or CD-ROM drive. That should be enough load
    to get the power supply started.
  4. DaveM

    DaveM Guest

    Several internet vendors stock PC power supply testers. MCM Electronics has a
    couple at


    Dave M
    MasonDG44 at comcast dot net (Just substitute the appropriate characters in the

    Some days you're the dog, some days the hydrant.
  5. AZ Nomad

    AZ Nomad Guest

    That depends on the color of cables the PS maker felt like using.
    You should learn where on the power connector those two leads are instead
    of relying on the PS maker following a particular color scheme.
  6. mistermaniac

    mistermaniac Guest

    Just build a dummy load with a bunch of resistors or so.
    If you connect green and black, an ATX power supply will switch o
  7. True, the diagram is available so i can check which pin it is.

    Bart Bervoets
  8. AZ Nomad

    AZ Nomad Guest

    I learned (at least on a 20 pin ATX), that if you have the connector
    facing you with the key to the right, shorting the two pins above the
    key will turn the power supply on.

    If it's been more than a few months since I last did the trick, I go
    to google to doublecheck.
  9. Guest

    I made a load consisting of a couple of old 12V tail light bulbs with
    10 watt resistors in parallel with the bulbs, so that they draw about
    3 amps each. I attached a regular power supply male connector
    to the wires so that I could plug it into one the the PS connector.
    This test rig is mounted on a little stand so that I do not have to
    worry about shorting the wires.
    This way I can test the 5V and 12V lines to see if they are working
    properly. I always use a DMM to check the actual voltages, but the
    test rig makes it easy to see if a supply is working.
  10. Ray L. Volts

    Ray L. Volts Guest
  11. Guest

    It doesn't address his question. It also says:

    "Be aware that a power supply may display proper voltages
    when nothing is connected to it, yet these voltages can fall

    below acceptable levels when a load is applied."

    This is correct, but more often, voltages will be out of tolerance not
    when a load is applied but unless a load is applied.

    I wouldn't rely on PC "technician" courses or guides for correct
    hardware information.
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