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Power supply questions:

Discussion in 'Electronic Basics' started by TLOlczyk, Jun 22, 2005.

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  1. TLOlczyk

    TLOlczyk Guest

    A power supply on one of my computers recently failed.
    ( I know it is the supply. I yanked another supply out of another
    computer, and this computer runs fine. I tried this supply in the
    other computer and it wont run. )

    A freind had an Compaq he wanted to throw out, so he gave it to me.
    The mobo connector on the power supply was correct but the leads in
    were the wrong color ( except for ground ). He also had a repair
    manual, the voltages it described matched the voltages in the ATX
    spec.

    So I attached a few old hard drives and fans to the power supply ( for
    a load ) and tried grounding the power on line. It wouldn't turn on.

    I then yanked the Compaq mobo, attached the power supply to the
    mobo, and turned it on. With the back exposed, I measured the voltages
    on each of the current carrying lines and they matched.

    I temporarily put in the power supply, and plugged it in. The computer
    came on when I plugged the supply into the 120, didn't have to push
    the button.

    So now I'm confused.

    Before I install the PS, I will have to take the connector from the
    old PS and wire it into the Compaq PS ( the leads on the connector are
    way short, the form factor of the supply seems off in that regard ).

    Here are the differences that I have noted in the manual and the ATX
    standard.


    Differnce one. A lead labeld Fan off on the Compaq is label PowerOK in
    the ATX spec.
    Difference two. One of the ground leads is specified as remote sensing
    on the Compaq. none are specified that way in the ATX standard.
    Difference three. One of the 3.3 leads is specified as remote sensing
    in both the Compaq and the ATX standard.

    I have no idea what remote sensing means in this case. Should I change
    those leads? Should I not use the remote sensing ground lead?

    Would that explain the power on without abutton push?
    Thanks.






    The reply-to email address is .
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    **
    Thaddeus L. Olczyk, PhD

    There is a difference between
    *thinking* you know something,
    and *knowing* you know something.
     
  2. Lord Garth

    Lord Garth Guest

    The problem is powerok also know as 'power good'. The motherboard
    outputs a signal to this input within a specific time frame or the ATX
    will shut off. If the motherboard does not provide this signal, you can
    jumper it to a 5 volt output. Lack of the power good signal is why you
    must keep the switch input grounded when it is not connected to a
    motherboard. Check your case switch, it is momentary.

    Sense inputs measure the power supply voltage at the load and adjust
    the voltage so as to be within spec.

    I would not be surprised to find similar connector with different pin
    outs on Compaq / HP or Dell systems. They want you to buy their
    over priced replacements.

    ATX power supplies are electronically switched. They can and do
    false. This is why you should switch off or unplug the supply when
    adding or removing cards from the slots.
     
  3. TLOlczyk

    TLOlczyk Guest

    Ok. I'm confused here. The mobo has a standard ATX connector and
    expects stqandard inputs. The power supply is different and doesn't
    have a powerok line ( instead it has a fan on line in it's place ).

    The funny behaviour I see is after I ( partially ) install the PS. It
    turns on the momment I connect the PS to a 120 outlet, not waiting
    for me to "push the button", which i find confusing.

    I haven't kept the system on for very long, but in the time that it is
    on, it stays on.
    So I guess that I should change the leads so that the connector
    matches up with the ATX spec with regards to sensing. The question is
    where do I put the grounded lead that is sensing. The ATX doesn't have
    anything like that in it.

    You point here isn't clear to me. Everytime I connect the PS to a 120V
    source it powers up. So this isn't some kind of "false" startup.




    The reply-to email address is .
    This is an address I ignore.
    To reply via email, remove 2002 and change yahoo to
    interaccess,

    **
    Thaddeus L. Olczyk, PhD

    There is a difference between
    *thinking* you know something,
    and *knowing* you know something.
     
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