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  1. #1
    Star Lounger
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    Power Supply Unit

    I replaced a faulty PSU, in a PIII 500Mhz, 256Mb RAM, 20Gb IDE HD, IDE
    CD-Drive, modem, separate 8Mb graphics card, desktop tower unit. The
    replacement PSU (which was a few years old) stopped working after a few
    days of use, so I replaced it with another.

    The first replacement I guessed was just unlucky, and may have been about
    to fail anyway. However, I've now just found out that the second
    replacement PSU has failed too.

    I don't think there has been a power surge in the house, as a laptop
    through the same supply has been OK. The monitor has it's own kettle lead,
    i.e. not powered through the computer, which should reduce the demand from
    the PSU.

    Any ideas about what I should check next before I try again?

    kind regards,

    Ian Price

  2. #2
    Uranium Lounger
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    Re: Power Supply Unit

    I'd be highly suspicious if two power supplies failed. Can you test them in another machine? It's quite possible that something on the mainboard is overdrawing and causing the PS to fail prematurely, such as the onboard power regulator.

    If your mainboard supports monitoring (and many do), you may want to download Motherboard Monitor 5 or something similar to check the voltages.
    -Mark

  3. #3
    2 Star Lounger
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    Re: Power Supply Unit

    Have a look at the capacitors on your motherboard. They are the cylindrical towers near the power connector, CPU and memroy. They look a bit like soda cans. They should be flat and shiney on top. If they are bulged or have black or tan crusty stuff on top your motherboard was also damaged. Fried capacitor juice indicates that the capacitor has blown, but most likely done it's job. They may put a greater than normal strain on the PSU if they have blown.

    The jobs of a capacitor are many, but your greatest interest here is that they do not allow AC current to pass. They also provide some spike (V) and frequency (Hz) protection. Too much voltage and they just get too hot to contain themselves. <img src=/S/aflame.gif border=0 alt=aflame width=15 height=15>

  4. #4
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    Re: Power Supply Unit

    All of the capacitors on the motherboard are shiny and don't seem to show any signs of damage as you describe?

    I think I'll try a new 300W PSU next just in case the used 200W units were not enough. Unfortunately I didn't make a note of the power on the orginal PSU that failed. I do know that the two that I've put in have been only 200W.

  5. #5
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    Re: Power Supply Unit

    I tested the failed PSU in another machine today and yes, it was completely dead.

  6. #6
    Uranium Lounger
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    Re: Power Supply Unit

    Let us know how the 300W power supply works out. Faster processors place more of a drain on them, and I'd think anything less than 250W would cause problems.
    -Mark

  7. #7
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    Re: Power Supply Unit

    The 200W units are from some P166 workstations that we got 5 years ago - I guess the PIII need a bit more juice? Will report back soon - hopefully with good news!

  8. #8
    Uranium Lounger
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    Re: Power Supply Unit

    Yes, if you're using power supplies from those older systems - it's almost a certain bet that you don't have enough juice. For PIII processors I wouldn't trust anything less than a 300W source!
    -Mark

  9. #9
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    Re: Power Supply Unit

    Good news, the computer is still working OK after a few days with the new 300W PSU - thanks for everyones' suggestions.

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