How to find the 5v line on a power supply?

Discussion in 'Computer Information' started by Doc, Jun 6, 2006.

  1. Doc

    Doc Guest

    Someone has suggested I test the 5V line on a power supply with a range
    holding multitester to see if it's staying steady and within range. How do I
    locate this line?

    Thanks.
     
    Doc, Jun 6, 2006
    #1
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  2. Doc

    beenthere Guest

    The cables that plug into your Hdrive are Red.Black.Black.Yellow
    Red and one Black = 5V.
    Yellow and one Black=12V.
     
    beenthere, Jun 6, 2006
    #2
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  3. Doc

    Guest Guest

    The pinout for the 20-pin ATX connector:

    http://xtronics.com/reference/atx_pinout.htm

    The pinout of the 24-pin connector (the most common type of 24-pin
    connector; there are 3 types):

    http://pinouts.ru/Power/btx_mbpower_pinout.shtml

    +5V = red
    +3.3V = orange (sometimes brown; blue with white stripe on some Dells)
    +12V = yellow
    +5V standby = purple
    -12V = blue
    -5V = white (not found on all power supplies)
     
    Guest, Jun 6, 2006
    #3
  4. Doc

    Mike T. Guest

    That's rather ridiculous advice, since myriad problems could
    I agree, to a point. But I still believe that replacing the power supply is
    a good idea, for many reasons. First, even good name-brand power supplies
    are surprisingly unreliable. The only component that fails almost as often
    is a floppy drive, and those are becoming more of a rarity. So it's good to
    have a spare power supply on hand anyway. You really lose nothing by
    swapping it. And, you reduce the risk that, if the other power supply was
    bad, it will damage other components. -Dave
     
    Mike T., Jun 6, 2006
    #4
  5. Doc

    Doc Guest

    It might be a moot point, apparently this Compaq power supply isn't
    something you can just grab off the shelf, it's form is non-standard.
     
    Doc, Jun 6, 2006
    #5
  6. Doc

    Arno Wagner Guest

    It is red. Ground is black.

    Arno
     
    Arno Wagner, Jun 7, 2006
    #6
  7. Doc

    kony Guest

    Err, no. Floppy drives almost never fail, I have several
    that are a decade old and just needed the heads cleaned.
    Cheap fans tend to fail quite often, and motherboards.
    Maybe a PSU more often than that, but a PSU failure is not
    more likely than "everything else" combined, including the
    operating system itself becoming infected, malfunctioning or
    being undermined by user action (configuration, registry,
    drivers, etc).

    If the other power supply were bad, it has already been
    powering the system you now allege it would damage. I
    suggest buying decent enough PSU that you have safety
    shutdown on it. System had ran for years and it takes only
    a few seconds to use a multimeter. Perhaps your method of
    checking voltage needs reconsidered if you have actually
    damaged gear while trying to take a voltage reading.

    It's good to have a spare everything- board, video, power,
    etc, but in the end there has to be reasonable suspicion it
    was power, and without the multimeter reading there often is
    not reasonable suspicion until AFTER one had changed the PSU
    and then found the problem resolved... or not resolved, then
    it was a waste of money and time. PSU do not fail often
    enough that it is reasonable to simply assume it is bad and
    immediately replace it, unless the PSU was a very poor match
    to the system (or low quality generic) to begin with.
     
    kony, Jun 7, 2006
    #7
  8. Doc

    kony Guest

    A lot of Compaqs were, but still used standard connectors to
    the mainboard. If the connector and wiring (voltages,
    pinouts) are the same then it need not be mountable in the
    chassis to just see if the system runs still or if there
    were another problem. Does the label on the PSU give any
    indicators? What system is this?

    As someone already mentioned, the drive plugs will have 5V.
    "usually" that is a red wire but proprietary gear including
    Compaq's has been know to stray from the standard color
    schemes from time to time. Looking at the 4 pin molex drive
    plug, with the tapered side of the connector facing up, 5V
    is the furthest left pin. If you accidentally had it upside
    down and it measured 12V, just take the reading of the
    opposite end since 5V is on one end, 12V on the other, and
    two (usually black) grounds inbetween.

    If this PSU is one Compaq made in the taller format, with a
    92mm fan on the back, it may not supply 5VSB (I don't recall
    for certain) but it supplies 3VSB. If you remain uncertain
    about anything take some good pictures and post to a server,
    linked here instead of posting the pictures themselves here.
     
    kony, Jun 7, 2006
    #8
  9. Doc

    Guest Guest

    Directron has a good selection of nonstandard and micro ATX (mATX)
    power supplies. Don't try another supply unless its connector wires
    match in color with those of the original supply's, pin for pin,
    because some incompatible supplies use mechanically identical
    connectors but have the wire colors arranged differently.

    I'm not sure what a range holding meter is. Many meters will hold at
    the peak voltage read, but this won't be very useful for your purpose.
    Better would be a fast-responding meter that can record minimum and
    maximum readings, as this can record the worst fluctuations over time.
    Voltage meters can't diagnose all power supply problems, but in
    practice supplies are OK when all their voltages remain well within
    tolerance.
     
    Guest, Jun 7, 2006
    #9
  10. Doc

    Guest Guest

    I had the highest failure rate with Mitsubishi 3.5" drives because
    their load mechanism would bind and cause the heads to clamp at the
    wrong time and scratch the disk or heads and sometimes even cause a
    head to tear off. My next most troublesome floppy drives were TEACs
    because their heads would go out of alignment.
     
    Guest, Jun 7, 2006
    #10
  11. Doc

    Guest Guest

    Guest, Jun 7, 2006
    #11
  12. Doc

    kony Guest


    a spot of grease might help on the former
     
    kony, Jun 7, 2006
    #12
  13. Doc

    kony Guest

    If it's the supply type I suspect it is, it's proprietary in
    pinout as well as form-factor. There were spares available
    online the last time I looked, the best luck at finding them
    is to enter the supply part/replacement numbers from it's
    label into Google, which may also provide an alternate part
    # that can also be sought.
     
    kony, Jun 7, 2006
    #13
  14. Doc

    Mike Berger Guest

    I'd classify that one as one of the really cheap ones.
     
    Mike Berger, Jun 7, 2006
    #14
  15. Doc

    Franc Zabkar Guest

    The power supply monitors its own voltage rails and lowers the POK
    signal if any are below spec. When this happens, the motherboard
    should normally reset/restart itself. Note that the voltage you
    measure at the PSU will be somewhat higher than what you measure on
    the motherboard. This is because of voltage drops in the harness and
    at the connector itself.

    - Franc Zabkar
     
    Franc Zabkar, Jun 7, 2006
    #15
  16. In theory, perhaps. In practice they're not that accurate and I wouldn't
    count on POK as any kind of proof the voltages are in spec.
     
    David Maynard, Jun 8, 2006
    #16
  17. Doc

    Guest Guest

    That typically doesn't occur until a voltage drops at least 15% below
    nominal value, or far below the normal 5% tolerance allowed for the
    voltages, and it's done more to protect any switching regulators on the
    motherboard, video card, or even disk drives, from reaching extreme
    duty cyclea rather than to prevent unreliable operation of the computer.
     
    Guest, Jun 8, 2006
    #17
  18. Doc

    CBFalconer Guest

    I prefer to do rough checks of power supplies with a scope probe,
    if available. That way you can see unusual ripple or other faults
    invisible to a voltmeter.

    --
    "Our enemies are innovative and resourceful, and so are we.
    They never stop thinking about new ways to harm our country
    and our people, and neither do we." -- G. W. Bush.
    "The people can always be brought to the bidding of the
    leaders. All you have to do is tell them they are being
    attacked and denounce the pacifists for lack of patriotism
    and exposing the country to danger. It works the same way
    in any country." --Hermann Goering.
     
    CBFalconer, Jun 8, 2006
    #18
  19. I'd guess its probably as good or better than most oem power supplies in any
    name brand computer (they usually use the cheapest crap you can get). I
    woudn't gurantee that it would deliver 400w but most computers don't need
    that much current.

    - Mike
     
    Michael Kennedy, Jun 8, 2006
    #19
  20. Well it is AMD certified... I've found that most AMD certified psu's are of
    acceptable quality.

    I know OEM's (dell, hp, compaq) aren't using Antec or any other quality
    psu's
     
    Michael Kennedy, Jun 8, 2006
    #20
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