Strange behavior of charging ic ISL88738H

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  • linhtinh
    Member
    • Sep 2020
    • 31
    • thailand
    #1

    Strange behavior of charging ic ISL88738H

    Dell LA-H331P board.

    Schematic here
    Boardview exactly same la-f541p here

    First is the ISL88738H charging ic died, i replaced it but the PQ1900+PQ1902 mosfets kept dying, all mosfets are taken from the donor board.
    Strange behavior is the machine still turns on without battery, i can still enter into bios, but when I pluggin the battery it doesn't charge.
    I measured all the capacitors and resistors around the charging ic, all are normal. Does anyone know why the PQ1900/1902 mosfets keep dying (shorted D-S) ?​
    Tags: None
    • mon2
      Badcaps Legend
      • Dec 2019
      • 14605
      • Canada
      #2
      1) Check if any of the other mosfets on this charger IC is shorted / leaky. Are you sure that the PQ1900/1902 mosfets are being soldered in the correct orientation for pin # 1? They are 100% the same mosfet as the original? Share the part number of the mosfet(s) that are dying. Post pics of the reworked area for these replaced parts.

      2) Confirm that the ISL88738 IC is soldered properly and without shorts.

      3) If the battery does not charge, confirm the battery is not defective. This is a DELL so the PSID communication on the DCin power connector is very important. Attach your power adapter and measure the voltage to ground of the PSID pin # 4 of the DCin power connector.

      Post the measurement. Without this 1-wire communication line, the logic board assumes the power adapter is underrated and will not charge the battery.

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