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Asus P5P800 SE - cold CPU, no voltage at the VRM

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    #1

    Asus P5P800 SE - cold CPU, no voltage at the VRM

    Hi,

    I have a P5P800 SE motherboard laying around, but it doesn't work. All caps are good quality and not bulging (mosty Panasonic FJ and six FL around the CPU), except five Chemicon KZG 16V 1000uF.
    The board will turn on, but nothing happens. The CPU doesn't heat up at all, yet the chipset does get hot as well as the GPU of the video card I plug in.
    And when I want to force it to turn off by shorting th two pins, it just won't so I have to unplug the PSU.
    I've checked the voltages at the VRM near the CPU and there is none. They don't seem shorted.
    I've soldered a buzzer where there was a room for it (but none originally installed) but it doesn't make any noise.

    Any ideas ?

    Thanks !
    Tags: None
    #2
    Re: Asus P5P800 SE - cold CPU, no voltage at the VRM

    You got a pic of the VRM section? My guess is something has gone open circuit. Are the VRMs supplied with any voltage at all?
    Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

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      #3
      Re: Asus P5P800 SE - cold CPU, no voltage at the VRM

      Yes I read close to 12V a the VRM supply. Do you want a photo of the VRM on my board ? Because nothing is burnt or obviously bad.

      There's some close up pics of the VRM on a forum :
      http://www.xtremesystems.org/forums/...r-p5p800se-plz

      Comment

        #4
        Re: Asus P5P800 SE - cold CPU, no voltage at the VRM

        Hmm, I'm not so used to repairing desktop boards - forgot there's never schematics!

        If I were you I'd try and figure out how that whole VRM section is sequenced. Test each MOSFET to make sure they're fully functioning and the numbers are all in order.

        Then check for shorts using the 200ohm setting between the legs of the MOSFETs and ground.

        If you don't find anything, you're best off going from that 12V voltage you found, and working your way through to try and find where the voltage drops off. Is DDR2 voltage present?

        Someone else probably has a better idea - I'm not too familiar with desktop VRMs.
        Dell E7450 | i5-5300U | 16GB DDR3 | 256GB SSD

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          #5
          Re: Asus P5P800 SE - cold CPU, no voltage at the VRM

          First things first, try reflashing the BIOS to rule that out. Also look for any bent pins in the LGA775 socket.
          Originally posted by PeteS in CA
          Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
          A working TV? How boring!

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            #6
            Re: Asus P5P800 SE - cold CPU, no voltage at the VRM

            I've put a BIOS chip from another P5P800 SE, it didn't change anything.
            The pins on the socket are fine.

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              #7
              Re: Asus P5P800 SE - cold CPU, no voltage at the VRM

              Could be Southbridge issues, judging by the fact that you can't turn OFF the motherboard after you turn it ON.
              Make sure all major circuits have proper power. You already found CPU VRM has no voltage on it. There's a few more to check:
              RAM Vcc
              Northbridge Vcc
              CPU Vtt (if CPU has one)
              Southbridge Vcc (unless motherboard NB and SB are merged together)
              Any other linear regulators (1117, 1084, 1085, 1086, 7805, etc.)

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                #8
                Re: Asus P5P800 SE - cold CPU, no voltage at the VRM

                is southbridge hot?
                common failure on these.

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