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Rail voltages before starting pc

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  • Rail voltages before starting pc

    I'm having trouble starting my boat pc. I typically have to remove the bios jumper and replace the cmos battery to get it to start, after it has been sitting there a while without power. Normally, the pc will power up, with fans, but not post.

    Now, I'm not even getting to the power idle up phase. I'm getting the intermittent "on" signal (short) to the motherboard, but it is not powering up.

    I checked the rail voltages and the only one I see is 5V (No 12V or 3.3V). Also, the 4-pin to the motherboard does not have voltage.

    MY QUESTION IS:
    Should all the rail voltages be on after the 12V is connected or does the motherboard send a signal back to the m2-atx to enable the 12V and 3.3V? The +, -, and ignition voltages are all correct. Just trying to see if the motherboard is the problem or if it isn't starting because only the 5V is being supplied.

    Thanks,
    Marc

  • #2
    i believe it does look for a 'life sign' from the motherboard-- where it shorts a signal wire to ground in the 20-pin harness.
    My OLD 2001 Mitsubishi Eclipse GT:
    "The Project That Never Ended, until it did"


    next project? subaru brz
    carpc undecided

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    • #3
      Originally posted by soundman98 View Post
      i believe it does look for a 'life sign' from the motherboard-- where it shorts a signal wire to ground in the 20-pin harness.
      Its the green wire on the ATX connector, short that to ground and the PSU should turn all the rails on. Otherwise only the +5v standby should be on. Essentially when the M2 tells the mobo to turn on it shorts the two pins that should be connected to the on switch pins on the mobo, and that, in turn, will short the green wire to ground (any of the black wires).
      -James
      Car: 2004 GTI VR6 24v Turbo 2.8L, GT35R, 630cc, Unitronic, Bosch 044, etc, etc..
      Main PC:i7 [email protected], 6GB DDR3, MSI X-58 Pro-E, Win 7 x64 RTM, Scythe Mugen2, 128GB G.Skill Falcon, 2x ATI4850 512MB Crossfire, Auzentech X-Fi Forte, Grado Labs SR-80

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      • #4
        Awesome. Thanks for the information.

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