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Possibly shorted FETS GA-MA770T-ES3

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    Possibly shorted FETS GA-MA770T-ES3

    Hi all, I got a Gigabyte GA-MA770T-ES3 AM3 board that I suspect has 2 shorted FETS as it become super hot to touch as soon as the PSU is switched on. I was unable to switch on the board, I am guessing the board has detected a short and don't allow me to turn on. But I was able to measure voltage on both of the suspected shorted MOSFETS:
    1) Highlighted in red, I was getting 4.9V (K3918)
    2) Highlighted in yellow, I was getting 0.4V (Nikos L1085DG)

    There was a Nichicon HM(M) 6.3V 1000uf next to the MOSFETS, highlighted in orange. When I was doing troubleshooting, I got no resistant on the leads of the caps, therefore I suspected it was the caps that had gone shorted, then I removed the caps for further testing. The cap was totally gone, although when testing out of circuit, there was resistant, but when I test it again using capacitance function, I am getting OL. After removing the cap, the MOSFETS still heatup as before.

    What your opinion guys ? Should I replace those MOSFETS ?
    Thanks in advance
    Attached Files

    #2
    Re: Possibly shorted FETS GA-MA770T-ES3

    Alright I figured out what wrong with the board, therefore prob is fixed.

    The LAN chip been shorted before the board was passed to me, as always I will touch the LAN chip whenever I sees a board that don't turn on / POST, this is because in my country there are still many people using phone line DSL internet, and always thunderstorm would fry the LAN chip. I did touch the LAN chip, but it is just a very very faint warm, therefore I tought it was normal. Until I replace the suspected shorted Nikos FETs with another Nikos N channel FETs. Now when connect the board to the PSU, now the LAN chip heat up real fast, I can't touch it for more than 1 sec. Immediately shut off the PSU and disolder the shorted LAN chip.

    So the conclusion was, the shorted LAN chip took the Nikos FETs and the Nichicon cap with it. Now I am able to turn on the board and passed memtest.

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      #3
      Re: Possibly shorted FETS GA-MA770T-ES3

      Good save!
      Would not have thought the LAN chip could burn those rather large MOSFETs. I guess we learn something new every day. Thanks for your post.

      Comment


        #4
        Re: Possibly shorted FETS GA-MA770T-ES3

        The L1085DG is actually a voltage regulator.



        Where did you measure voltage?
        Last edited by lti; 04-19-2016, 05:55 PM.

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          #5
          Re: Possibly shorted FETS GA-MA770T-ES3

          Originally posted by lti View Post
          The L1085DG is actually a voltage regulator.
          You're right!
          Anything with 1085 or 1086 in the part number is more than likely a voltage regulator.

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