HP 520 LA-3491P High Side MOSFET Heat Problem

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  • Lex-
    Member
    • May 2011
    • 18
    #1

    HP 520 LA-3491P High Side MOSFET Heat Problem

    1.8v rail shorted, PQ16 high side mosfet of the 1.8v rail badly damaged with a hole on the middle of it, SI4800 maybe, can´t read it, replaced with FDS8884 as indicated in the schematic, now the 1.8v rail present but PQ16 heats up a lot instantly, can someone have an idea on what to check please ?

    Also disconnected PJP4 no change, PQ16 heats a lot !

    Schematic:
    Attached Files
    Last edited by Lex-; 11-09-2017, 06:40 PM.
    Tags: None
    • Lex-
      Member
      • May 2011
      • 18
      #2
      Re: HP 520 LA-3491P High Side MOSFET Heat Problem

      Someone who can help me please ?

        Comment

        • caspian
          Badcaps Legend
          • Oct 2015
          • 1589
          • Laptop
          #3
          Re: HP 520 LA-3491P High Side MOSFET Heat Problem

          check the 19v rail for being shorted to ground. If it was shorted, search the entire mainboard to see why 19v is shorted. do not plug the laptop in until the short is gone.
          Last edited by caspian; 11-12-2017, 04:41 AM.

            Comment

            • khaahk
              Badcaps Veteran
              • Dec 2013
              • 743
              • Estonia
              #4
              Re: HP 520 LA-3491P High Side MOSFET Heat Problem

              What is resistance from PL7 to gnd after PJP4 open?
              PU11 might be dead after PQ16 shorted.

                Comment

                • Lex-
                  Member
                  • May 2011
                  • 18
                  #5
                  Re: HP 520 LA-3491P High Side MOSFET Heat Problem

                  caspian:

                  19v rail not shorted to ground.


                  khaahk:

                  Fluke 26III, red probe connected to ground, black probe connected to PL7:

                  ohms scale: 0.892 k ohms

                  continuity (beep) scale: 149.3 ohms
                  Note: if I invert test probes (black to Gnd, red to PL7) then no read -OL.-

                  Thank you.

                    Comment

                    • Lex-
                      Member
                      • May 2011
                      • 18
                      #6
                      Re: HP 520 LA-3491P High Side MOSFET Heat Problem

                      Originally posted by khaahk
                      What is resistance from PL7 to gnd after PJP4 open?
                      PU11 might be dead after PQ16 shorted.
                      Fluke 26III, red probe connected to ground, black probe connected to PL7:

                      ohms scale: 0.892 k ohms

                      continuity (beep) scale: 149.3 ohms
                      Note: if I invert test probes (black to Gnd, red to PL7) then no read -OL.-

                      Any advice ?

                      Thank you.

                        Comment

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