A1706 820-00923 CPU gets warm, no post

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  • Beeldbuisje
    Senior Member
    • Jul 2020
    • 57
    • Belgium
    #1

    A1706 820-00923 CPU gets warm, no post

    This MacBook is fallen on is back, says the previous owner, after this nothing.

    Every tension on the CPU is present. With board disconnected, board takes first 820 mAmps, falls down to 720, falls down till 666mAmps and stays.
    No backlight enable signal, no post signal and CPU gets warm. After a while the fans starts spinning because of the hot heatsinks.

    Long press on the TouchID button switches the laptop off and 2nd press back on. Battery charges and on battery the same behavior.

    CPU reballed, no improvement.

    Dead CPU, or other clues?

    Might this be a dead BIOS rom chip?
    Tags: None
    • Beeldbuisje
      Senior Member
      • Jul 2020
      • 57
      • Belgium
      #2
      Re: A1706 820-00923 CPU gets warm, no post

      update: ALL_SYS_PWR_GOOD is high, which proves the well functioning of all power lines.
      I mesured with oscilloscope SPI_MLB_IO1_MISO and SPI_MLB_IO0_MOSI and there's communication visible till the current drops to 666mAmps.

      Removed BIOS chip and current stays on 500mAmps. CPU seems to read from BIOS.

      Anyone who could tell something more with this update?

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