PSU test results - what does it mean?

By detrunks
Oct 21, 2010
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  1. Hi,
    My PC recently started to freeze so I did a PSU test with a tester & it showed no -5v LED when testing the 24pin connection. I bought a new PSU and had the same problem with the PC. I tested the new PSU and again it showed no light for -5v. What is going on?? Is it coincidence both PSUs failed on -5v or is my set damaging the PSU? The old PSU was an enermax 650x and the new one is a coolermaster 600w. I don't really need the wattage but it was always in case of an upgrade.

    Please help!!

  2. Edward Catflap

    Edward Catflap TS Rookie Posts: 17

    Either your tester's dodgy or you've got a case of really bad luck and two faulty PSUs. If the -5v rail test light isn't on, I can only assume that there's no current going through it. If it's the type of tester I think it is;

    Green = in range (close enough to the correct voltage - think tolerance is about 5%)
    Red or Orange = out of range (too high or too low; faulty)
    No LED = Immediate fail or the pin isn't conducting properly with the tester

    Check out the pic below (hope it works) and see if that pin is connecting with the corresponding pin on the tester. If it is, then yeah. Broken tester or broken PSUs.


    Most testers are fine, but just like all other electronic items it could be faulty... I'd be tempted to try another tester or confirm with a 3rd power supply - preferably one that IS already tested to be okay. It's highly unlikely your tester is breaking the supplies.

    If it's starting to freeze, give your machine a RAM test and Hard Drive test. If they both pass it's likely (likely! not definitely!) software - nothing a format/reload can't fix :)

    Hope that helps mate.
  3. Route44

    Route44 TechSpot Ambassador Posts: 11,966   +70

    First, very nice diagram there Edward Catflap. Where did you get it? That is a nice clear teaching tool.

    Second, I could be mistaken but isn't the -5v not considered that important anymore?
  4. Edward Catflap

    Edward Catflap TS Rookie Posts: 17

    There's your link Route44 :) the tutorial covers the basics really well .

    You could be right about the aged -5v. I might be mistaken myself, but I believe it was more important in older Pentium models, back before the 24-pin ATX standard came out. Would definitely explain why his computer's starting if there was no -5v output, haha. I only know for certain the need for a PG value has been almost certainly phased out (yet it's found on modern testers...).
  5. Route44

    Route44 TechSpot Ambassador Posts: 11,966   +70

    Thanks for the link. Much appreciated. I think you are correct about the -5v being important for the older tech.

    When testing a psu I prefer a digital multimeter but not everyone knows how to use one.

    Keep up the good work.
  6. captaincranky

    captaincranky TechSpot Addict Posts: 11,457   +1,759

    I simply hate to sound ungrateful, but the diagram is of the older style 20 pin ATX connector.

    If you have access to the 24 pin diagram, that would be super. (Yeah, yeah, I know, pins 1 through 20 are the same).

    Oh, never mind, here's a side by side comparison;

    Anyway, as Route44 has pointed out, a digital multimeter would be a better choice. With that tool, you can probe the connector block with the computer in operation, and all the voltage taps would be properly loader.

    Plan "B" would be hardware monitor software, as that will tell you what the voltages are, simply by opening the program.
  7. Route44

    Route44 TechSpot Ambassador Posts: 11,966   +70

    DUH-me! You're right Captain. Thanks for catching this.
  8. seanc

    seanc TS Rookie Posts: 88

    -5v is seldom, maybe even never included on power supplies now.
    I also suggest a digital multimeter for testing voltages.
    Be sure to add a load to the power supply, put a couple of hard drives and an optical drive on.

    You could also try a digital power supply tester such as the one from Antec, however I have't tested its results against a multimeter yet.
  9. Route44

    Route44 TechSpot Ambassador Posts: 11,966   +70

    Thanks for the confirmation on the -5v, seanc.

    I have a Craftsman didgital multimeter that you can get for $20 and it does the job nicely.
  10. Edward Catflap

    Edward Catflap TS Rookie Posts: 17

    Crap. Good catch :p

    detrunks, how did you go with the freezing issue? Did you manage to get it fixed?

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