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ATX power supply question

Discussion in 'Electronic Repair' started by Charlie Bress, Mar 15, 2006.

  1. I am working on an older HP Pavilion Model 6830.
    The first complaint is that it would not turn on. I pressed the on switch
    several times and it fired up.
    Now it will not shut down. Even pulling out the line cord doesn't reset it.
    Plug the cord back in and it is still on. The p/s is an ATX-105.

    There is nothing else attached. No keyboard, no monitor. I am just going by
    the sound of the fan and front panel LED.

    The power on switch goes to the mobo through a connector. Unplugging this
    connector and testing the switch it tests good for continuity. It is a
    momentary contact switch which tells me that there is latch someplace. Is
    this latch somewhere on the mobo or is it in the p/s itself?

    Advice please.

    Charlie
     
  2. jakdedert

    jakdedert Guest

    Hold down the switch for five seconds or so....

    jak
     
  3. Dave D

    Dave D Guest

    Check the bios- there's often a setting to configure the power switch mode,
    and whether the PC switches back on automatically after a power failure, or
    unplugging the mains lead in your case.

    If you still have no luck, trying clearing the CMOS. There's usually a
    jumper on the motherboard to achieve this. I've known a corrupted CMOS to
    cause some very strange symptoms.


    It is quite common for ATX motherboards to require the power switch to be
    held in for several seconds to power down, as jakdedert suggests.


    Dave
     
  4. That feature requires ( I believe) that the OS is running. I never get that
    far
    And unplugging the .power line for an extended period should reset a normal
    system.

    But I will try it anyway just because I have been wrong before.

    Charlie
     
  5. Dave

    Dave Guest

    No, it's a BIOS-level feature. You can set it so that the PC turns on when
    the line is connected as noted above so that if, for example, you're running
    a web server for your business, you don't have to turn it back on if there's
    a power failure. My system allows you to "return to previous state" when
    the power is re-applied, i.e. if it was off when the power died, it stays
    off, and vice versa.
     
  6. New News

    I tried holding the power switch down but still no shut down.
    And then I took an old p/s that is not a mini and won't fit the box and
    plugged it into the mobo and one drive to draw some power.
    This supply also came on when the power cord was plugged in and it too could
    not be shut down with the power button.
    Unless someone has a better idea I am almost convinced that it is a mobo
    problem.

    Charlie
     
  7. James Sweet

    James Sweet Guest

    I've seen this problem a few times caused by bad electrolytic capacitors
    in the power supply. Often the PSU is just replaced though, unless it's
    a high end one it probably isn't really worth fixing unless you just
    want the challenge.
     
  8. Dave D

    Dave D Guest

    It certainly sounds like a motherboard problem, did you try my suggestions
    like clearing the CMOS?

    Have you tried removing all but essential hardware, and have you tested the
    memory?

    Have a close look at the electrolytic capacitors on the motherboard and
    check they aren't domed and/or leaking. Apart from that, there's not much
    you can do but replace the motherboard.

    Dave
     
  9. Andy Cuffe

    Andy Cuffe Guest

    It's probably not the power supply. The power it turned on and off by
    the motherboard. The front power switch just tells the motherboard to
    send the power on signal to the power supply. Check the motherboard
    for bad caps near the CPU:

    http://cquirke.mvps.org/badcaps.htm

    If you don't see any of those, try removing the CMOS battery (a flat
    "watch" battery on the motherboard) and leaving it unplugged over
    night. Check that the CMOS battery reads at least 3v. A bad CMOS
    battery can cause problems.
    Andy Cuffe

     
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