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power supply repair question...

Discussion in 'PC Hardware' started by Kenabi Tsuki, Jul 22, 2004.

  1. Kenabi Tsuki

    Kenabi Tsuki Guest

    i know the typical answer "replace it!" but i don't
    want that answer, i want to know what it is that
    causes this particular problem.

    constant reset, works great for about as long as it
    takes to get to the os itself, and then resets.

    what exactly is it in the power supply that causes
    this behavior? an ic? a capacitor? diode? i have a
    few power supplies laying around i'd like to fix
    this problem on since i like the way they managed
    before they started this. and i know it's possible
    to fix them. i just don't know what it is that
    causes it.

    any info/directions to places of possible help
    would be much appreciated.

    -Tsuki
     
    Kenabi Tsuki, Jul 22, 2004
    #1
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  2. Kenabi Tsuki

    Arno Wagner Guest

    It could be almost anything. If you really want to go through with
    it, first step is to do a full shematic and get the datasheets
    of all components involved. Then get a Matser's in ee with
    focus on power electronics. Get the needed measurement equipment.

    At that point you will have a reasonable chance of finding
    out what the problem is.

    Sorry.
    Arno
     
    Arno Wagner, Jul 22, 2004
    #2
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  3. Kenabi Tsuki

    Ron Cook Guest

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    The symptom could have many causes; not all need be related directly to the
    power supply.

    A failing or overheating video card (or other card or component) could be
    drawing more current than the power supply is designed to provide.
    This will cause a correctly-designed supply to shut itself down.
    If the fault is removed (when the device cools down, as an example) the unit
    may reboot.

    A temperature-related short circuit on a card or on the mainboard should
    cause the power supply to shutdown.

    One method to use for testing is to use a digital multimeter to measure the
    voltages supplied by the power supply during boot.

    Measure the 12-volt and 5-volt lines (rails) specifically.

    Also, try disconnecting everything not required for the POST routine.
    Then, re-connect one item at a time (while the machine is powered off). You
    may find that a specific device, such as a hard drive, is causing the
    forced reboot.

    - --
    Ron n1zhi

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    Ron Cook, Jul 23, 2004
    #3
  4. Kenabi Tsuki

    Mike Scott Guest

    Ron Cook wrote:
    ....
    I has a similar problem in an old PII, temperature-related. Replacing
    the psu alleviated it a bit, or seemed to. Eventually turned out to be
    the processor.....

    I assume you've swapped the psu for a known good one?
     
    Mike Scott, Jul 23, 2004
    #4
  5. Kenabi Tsuki

    Kenabi Tsuki Guest

    heh. i don't want to "replace" it, it's just sitting around as it is.
    i want to repair it. but alas, the only answer i'm getting is "go get a
    degree and check every part in the thing." which is, to say the least.
    incredibly unhelpful. there has to be something in there that's fairly
    standard to cause this problem. more so since i've never had this
    problem from an at... you know, i think it might be the IC or some of
    the components around it, that is hooked to the 'power good' lead.

    it's amazing what you think of when you least expect it, time to go a
    huntin...

    -Tsuki
     
    Kenabi Tsuki, Jul 23, 2004
    #5
  6. Kenabi Tsuki

    PLS Guest

    Not sure what you expected. You describe a problem
    that typically is hardware failure related to something other
    than
    the power supply. You've done no testing, and you want
    answers? If you had at least bought a multimeter and
    figured out what portion(s) of the supplies were
    failing, perhaps you might have gotten some help, but
    your original post was useless in that regard. Frankly, what
    you described is rarely a supply problem unless the supply
    is under rated for the machine, and to have multiple ones
    is bizarre to say the least.
     
    PLS, Jul 23, 2004
    #6
  7. Kenabi Tsuki

    Mike Scott Guest

    I understand that. But we're asking if you are *sure* it's the psu at
    fault. And the quickest way of doing this is to swap it for a known
    good unit -- temporarily scavenge one from another m/c if necessary --
    and see if the problem goes away. You could waste a lot of time trying
    to fix a psu fault if the problem were really in, say, the mobo!

    (BTW, don't forget there's plenty of exposed mains voltage inside the
    psu. That's why they're normally regarded as non-repairable units)
     
    Mike Scott, Jul 23, 2004
    #7
  8. Kenabi Tsuki

    Kenabi Tsuki Guest

    one of the "problem" psu's came out of the box i'm typing this on,
    some moths ago. having tried it in all of my machines without the drives
    hooked up, they all exhibit the same symptom: getting to just before the
    OS loads and resetting, about every 8 seconds, consistantly. and yes,
    i'm aware of whats inside a psu ;o

    i'm not exactly a "newbie" ;o

    one of the psu's has a power_ok lead going to a 4pin inline ic
    the other one i'm still tracing. the ic i found isn't testing shorted,
    and the power input to it reads at a constant 4.97v

    so perhaps it's not that.

    hrmm.. lacking an oscilliscope hinders this search.

    -Tsuki
     
    Kenabi Tsuki, Jul 24, 2004
    #8
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