acer la-e921p shorting mosfet

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  • myth77
    Badcaps Veteran
    • Feb 2017
    • 380
    • Croatia
    #1

    acer la-e921p shorting mosfet

    Dont know history of the laptop.... but the laptop was completely dead and will not power on..
    Checked and found short on 19vb line... and found pq1402 mosfet shorted pin 7 (NVVDDS_SW1) and 2 (+19VB_NVVDDS), second mosfet pq1401 was ok.
    When replace it i get 19v but when powering on i see fans spin then nothing...then i checked again...short on same mosfet.

    Then i investigate more and found very low ohm resistence between pin 1 and 20 on pu1401 so i replaced it, also replaced pr1401 (dead, showing 60 ohms)...and started motherbaord again..this time the laptop did several times restarting...i cen felt cpu heating...then again nothing..so i checked again short on pq1402!?

    Dont know where to look more? what is shorting mosfet? any ideas?

    Attached boardview and schematic
    Attached Files
    Tags: None
    • Sephir0th
      Badcaps Legend
      • Oct 2020
      • 1262
      • Germany
      #2
      Re: acer la-e921p shorting mosfet

      PQ1402 PIn 2 and 7 are shorted with what? With ground or with each other? If there was Continuity beetween this Pins, there was probably 19V going straight to your GPU...

      I don't know the correct Resistance between this two rails in PU1401, but a new reading after replacing the IC Would give us a hint.

      What is the exact Resistance of PL1401 to ground in Ohms?
      Last edited by Sephir0th; 01-02-2021, 07:48 AM.
      FairRepair on YouTube

        Comment

        • myth77
          Badcaps Veteran
          • Feb 2017
          • 380
          • Croatia
          #3
          Re: acer la-e921p shorting mosfet

          Yes, they are shorted with each other...and yes my thoughts exactly, probably 19v going through gpu...but resistence to ground on pl1401 is arround 2 ohms....?
          And why they keep shorting?

            Comment

            • Sephir0th
              Badcaps Legend
              • Oct 2020
              • 1262
              • Germany
              #4
              Re: acer la-e921p shorting mosfet

              Maybe you're Lucky and the GPU is still Alive. However, Something Is wrong in this area. You Said PQ1402 is fine. So did you compared voltages & resistances on the Gate-Pins between PQ1401 and PQ1402. Maybe the high Gate is Open all the time. Checked the "shorted" Mosfet Out of the Board to confirm the short? Did I Understand it right that you already have replaced PU1401? If you don't find Something obvious, i believe We need a complete measurement if PU1401.
              FairRepair on YouTube

                Comment

                • myth77
                  Badcaps Veteran
                  • Feb 2017
                  • 380
                  • Croatia
                  #5
                  Re: acer la-e921p shorting mosfet

                  Originally posted by Sephir0th
                  Maybe you're Lucky and the GPU is still Alive. However, Something Is wrong in this area. You Said PQ1402 is fine. So did you compared voltages & resistances on the Gate-Pins between PQ1401 and PQ1402. Maybe the high Gate is Open all the time. Checked the "shorted" Mosfet Out of the Board to confirm the short? Did I Understand it right that you already have replaced PU1401? If you don't find Something obvious, i believe We need a complete measurement if PU1401.
                  i checked mosfet outside board and shorted...This two mosfets are in parallal and they have the same pins for gates, source and drain...I wrote it wrong..it is allways pq1402 that is shorted..and pq1401 stays alive (probably this proteced gpu...if it is alive)
                  Yes it seems that i will have to check every pin, resistor...near this area...

                    Comment

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