Dead Gibabyte mobo!!!

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  • kgavionics
    Senior Member
    • Apr 2017
    • 152
    • Canada
    #1

    Dead Gibabyte mobo!!!

    Hi guys
    I bought a Ga-p55-us3l from ebay and i have a weird problem as far as i can tell.
    When i plug the atx24 pins connector along with the 12V 4 pins atx connector, the motherboard doesn't show any sign of life( phase led light off ) cpu and gpu fans are off and of course no post or whatsoever.
    When i disconnect the atx12v connector ,the cpu fan starts to turn and the CPU phase lights come on.
    I have a good electronics background, but i've never tried to fix a mobo before!!
    I want to do some troubleshooting, but i don't have any schematic and i don't know where to start from!
    can someone help me please!!!
    Tags: None
    • ktmmotocross
      Boardkiller
      • Feb 2014
      • 3580
      • slovakia
      #2
      Re: Dead Gibabyte mobo!!!

      as this connector is for added CPU power, check this line for short

        Comment

        • piernov
          Super Moderator
          • Jan 2016
          • 4435
          • France
          #3
          Re: Dead Gibabyte mobo!!!

          Shorted MOSFET on CPU VCore VRM. Measure exact resistance between +12V and ground inside this P4 CPU power connector (+12V is the pins that connect to yellow wire, ground is the pins that connect to black wire), with the power supply cable actually disconnected.
          OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

            Comment

            • kgavionics
              Senior Member
              • Apr 2017
              • 152
              • Canada
              #4
              Re: Dead Gibabyte mobo!!!

              Originally posted by piernov
              Shorted MOSFET on CPU VCore VRM. Measure exact resistance between +12V and ground inside this P4 CPU power connector (+12V is the pins that connect to yellow wire, ground is the pins that connect to black wire), with the power supply cable actually disconnected.
              Thank you guys for your inputs
              I have a short between the 12V rail and ground inside the connector!
              i have found some shorted source and drain on some Mosfet's ( K4212)
              I guess this Mobo is not worth fixing!!!
              I only want what could went wrong!!could be a bad Power supply unit, because i have tried this board with a cheap Power supply and since then i ended up having this problem and two defective CPU's?

                Comment

                • ktmmotocross
                  Boardkiller
                  • Feb 2014
                  • 3580
                  • slovakia
                  #5
                  Re: Dead Gibabyte mobo!!!

                  it's just mosfet/s, replace check caps and it will be good to go

                    Comment

                    • ala_borbe
                      aka Donald
                      • Apr 2011
                      • 1625
                      • Malta
                      #6
                      Re: Dead Gibabyte mobo!!!

                      yes, this type of repairs last long
                      Im Back... sort of...

                        Comment

                        • kgavionics
                          Senior Member
                          • Apr 2017
                          • 152
                          • Canada
                          #7
                          Re: Dead Gibabyte mobo!!!

                          i'll check if i can find some good deal on these Mosfet's on ebay or aliexpress!!!
                          thank you guys for your inputs
                          best regards

                            Comment

                            • ktmmotocross
                              Boardkiller
                              • Feb 2014
                              • 3580
                              • slovakia
                              #8
                              Re: Dead Gibabyte mobo!!!

                              mosfets is mosfets. u can keep it from another mobo or gpu.

                                Comment

                                • piernov
                                  Super Moderator
                                  • Jan 2016
                                  • 4435
                                  • France
                                  #9
                                  Re: Dead Gibabyte mobo!!!

                                  I don't have the same point of view there… CPU VCore MOSFETs are quite sensitive in my experience. Only replacing the shorted one with random MOSFET from Aliexpress always resulted in the board dying again.
                                  For piece of mind I replace all the high-side (or low-side) MOSFETs with ones from the same batch, avoiding Chinese eBay seller or Aliexpress. I also replace the PWM controller for the MOSFET that died, or if everything is integrated into the CPU buck controller itself I replace it as well.
                                  OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

                                    Comment

                                    • ktmmotocross
                                      Boardkiller
                                      • Feb 2014
                                      • 3580
                                      • slovakia
                                      #10
                                      Re: Dead Gibabyte mobo!!!

                                      im not replacing for random from aliexpress. im mostly using used genuine from used mobo and mostly with higher walues

                                        Comment

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