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  1. #1
    Billy T
    Guest

    Default "Power Good" & Motherboard arguing the toss?

    Hi Team

    Some time back I posted about my PIII 550 not booting at switch-on and requiring a reset to get going. MB is an Intel 440BX BTW.

    I've checked the 5 volt "power good" signal and it comes up at switch on every time without fail, but 9 times out of 10 I need a reset to start the boot process. All plugs etc are well seated.

    Maybe the timing of the PG signal is out, but I can't really see that being an issue as the boot window has to be wide enough to allow the PSU ouput to rise fully, and I have previously picked up a PG signal by paralleling from a normal 5 volt line on a PSU that was too cheap to offer such technical niceties and that worked fine.

    I suppose this could also be a fault on the MB that clears intermittently, but is there anything else I could or should look at before I build an auto-reset module into the beast to save me having to manually kick-start it?

    Cheers

    Billy 8-{)

  2. #2
    yang11
    Guest

    Default what kind of video card?

    have u upgraded the bios ?

  3. #3
    godfather
    Guest

    Default Re: "Power Good" & Motherboard arguing the toss?

    I have resorted to a good "simple" low tech reset circuit in the past:

    Using a subminiature relay, N.O. contacts wired across the reset pins.
    Putting 100 microfarad (or to suit the relay used) electrolytic capacitor in series with the relay coil (observing polarity).
    At switch on, the capacitor charging current pulls in the relay, releasing it when it is charged, some milliseconds later.

  4. #4
    Billy T
    Guest

    Default Re: "Power Good" & Motherboard arguing the toss?

    *Snap* God

    Antenna relay ex Tait 104 VHF RT is on desk, now looking for suitable cap in garage junque box.

    The simple, low-tech solutions are so often the best!

    Cheers

    Billy 8-{)

  5. #5
    Graham L
    Guest

    Default Re: "Power Good" & Motherboard arguing the toss?

    The way it is supposed to work is that the motherboard holds the CPU (not necessarily any I/O buses) in the reset state until the PowerOK signal comes through from the PS. The PowerOK is supposed to be raised some time (tens or hundreds of ms) after all supplies have stabilised.

    Cheapo supplies might just connect the PowerOK to the +5V supply. That would work most of the time. Until you start getting microwave clocks. :-(
    GF's idea should work. There are more modern ways to do that ... there's a three terminal device in a TO-92 which does this (I think Dallas call it a "brown-out detector") , and there's always the good old 555. I suppose you could programme up a Pic-AXE too.

  6. #6
    Billy T
    Guest

    Default Re: "Power Good" & Motherboard arguing the toss?


    > GF's idea should work. There are more modern ways to
    > do that ... there's a three terminal device in a
    > TO-92 which does this (I think Dallas call it a
    > "brown-out detector") , and there's always the good
    > old 555. I suppose you could programme up a Pic-AXE
    > too.

    Aarrrrrrrrrrggggggghhhhhhhhhh

    TMT: Too much technology. Otherwise known as creeping elegance.

    You keep the Pic-AXE Graham, I'll just use the handle.

    Cheers

    Billy 8-{)


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