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Thread: Power Supply Testing - AT Power Supplies / ATX Power Supplies with Load

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    Default Power Supply Testing - AT Power Supplies / ATX Power Supplies with Load

    I have read and seen many articles about how to short an ATX Power supply to test power for it and then using a multimeter to check the voltages. The articles also mention best to test them under load. But what I dont see in the articles is what exactly is being used to provide the load on the machines. So what would be good to hook up to the supplies to give them a good test with load?

    Secondly, is there a way to test an AT Power supply in the same way? Or is the best option to hook up an AT to ATX Adapter and test from the adapter?
    "In Life, The Days Are Long But The Years Are Short..."

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    You can buy an ATX PSU tester, which puts a resistive load on it, but I usually just use a HDD. You just need something that will pull amps off of the 12V and 5V rails, a spinning hard drive does this quite well.

    And yes, you can use the same process to test an AT PSU, you just don't need to ground out a wire coming from the supply, you can just flip the switch.

    One big diff between an ATX and an AT PSU is that an ATX PSU should power up when the PowerOn wire is grounded regardless of a load, whereas an AT PSU will probably not power up at all when the switch is flipped when there is no load on it. I've even seen them push out 12V and 5V for a few seconds before dropping to 0v due to the lack of a load.

    IBM 5160 - 360k, 1.44Mb Floppies, NEC V20, 8087-3, 45MB MFM Hard Drive, Vega 7 Graphics, IBM 5154 Monitor running MS-DOS 5.00
    IBM PCJr Model 48360 640kb RAM, NEC V20,, jrIDE Side Cart, 360kb Floppy drives running MS-DOS 5.00
    Evergreen Am5x86-133 64Mb Ram, 8gb HDD, SB16 in a modified ATX case running IBM PC-DOS 7.10

  3. #3

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    A Known working Motherboard and Hard drives are good choices, When i test PSU's i load them up with a good motherboard and a few hard drives and leave the PSU running whilst checking the output voltages over a period of time, I do that with AT and ATX PSU's.

    Don't rely on an "ATX power supply tester" as they can often tell you an ATX is good when infact it's not, I have one and only use it because it shows Voltages and PG time on screen, Basically nothing more than a glorified DMM.

  4. #4

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    It depends on the PSU, Just like some AT PSU's won't power up without a load, Not all ATX PSU's power up without a load either, best thing to do is attach a load regardless.

    Quote Originally Posted by lutiana View Post
    ...One big diff between an ATX and an AT PSU is that an ATX PSU should power up when the PowerOn wire is grounded regardless of a load, whereas an AT PSU will probably not power up at all when the switch is flipped when there is no load on it. I've even seen them push out 12V and 5V for a few seconds before dropping to 0v due to the lack of a load.

  5. #5

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    And sometimes the puny 3" IDEs aren't sufficient load to get the desired result. A FH 5" Maxtor Monster (or other brand) will surely provide the correct outcome.
    If you're looking for DS/DD or DS/HD 3" or 5" floppy disks, PM me. I've got some new, used, and factory over-labeled disks for sale.

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    Quote Originally Posted by Stone View Post
    And sometimes the puny 3" IDEs aren't sufficient load to get the desired result. A FH 5" Maxtor Monster (or other brand) will surely provide the correct outcome.
    There ya go: start marketing those doorstops of yours as high-tech Universal Dummy Loads!

  7. #7

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    Quote Originally Posted by MikeS View Post
    There ya go: start marketing those doorstops of yours as high-tech Universal Dummy Loads!
    Brilliant!
    If you're looking for DS/DD or DS/HD 3" or 5" floppy disks, PM me. I've got some new, used, and factory over-labeled disks for sale.

    There is a crack in everything. That's how the light gets in. -- Leonard Cohen
    ☞ Time flies like an arrow; fruit flies like a banana.

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    Thanks for the information.

    I ask as I fear the AT Power supplies in a couple of my older PC's (486 and Pentium 1) that I built will go bad and take other hardware with it. They seem fine now, they work and run when the computer is on. But I havent had either on for an extended period of time (hours consecutively) and I am worried about them damaging the rest of the system if I do.
    "In Life, The Days Are Long But The Years Are Short..."

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    Quote Originally Posted by Smack2k View Post
    Thanks for the information.

    I ask as I fear the AT Power supplies in a couple of my older PC's (486 and Pentium 1) that I built will go bad and take other hardware with it. They seem fine now, they work and run when the computer is on. But I haven't had either on for an extended period of time (hours consecutively) and I am worried about them damaging the rest of the system if I do.

    Grab a hard drive that you don't really care about, plug it into the PSU and unplug everything else then turn the PSU on and just walk away. Come back in an hour and check the voltages, then walk away again and come back and check it every now and again. If you get through 12 hours and the voltages don't change much and the HDD is still spinning then I'd say you have a good PSU.

    IBM 5160 - 360k, 1.44Mb Floppies, NEC V20, 8087-3, 45MB MFM Hard Drive, Vega 7 Graphics, IBM 5154 Monitor running MS-DOS 5.00
    IBM PCJr Model 48360 640kb RAM, NEC V20,, jrIDE Side Cart, 360kb Floppy drives running MS-DOS 5.00
    Evergreen Am5x86-133 64Mb Ram, 8gb HDD, SB16 in a modified ATX case running IBM PC-DOS 7.10

  10. #10

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    Quote Originally Posted by Smack2k View Post
    I ask as I fear the AT Power supplies in a couple of my older PC's (486 and Pentium 1) that I built will go bad and take other hardware with it. They seem fine now, they work and run when the computer is on. But I havent had either on for an extended period of time (hours consecutively) and I am worried about them damaging the rest of the system if I do.
    Why do you say that?

    How would that happen?
    If you're looking for DS/DD or DS/HD 3" or 5" floppy disks, PM me. I've got some new, used, and factory over-labeled disks for sale.

    There is a crack in everything. That's how the light gets in. -- Leonard Cohen
    ☞ Time flies like an arrow; fruit flies like a banana.

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