820-01958 - Missing PP3V3_S5 - No liquid damage

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  • duwane
    Senior Member
    • Mar 2022
    • 55
    • New Zealand

    #1

    820-01958 - Missing PP3V3_S5 - No liquid damage

    Hi All.

    I have an 820-01958 T2 board from a 2020 A2179 that does not want to boot.

    No visible signs of any liquid damage. Green/orange light is present on charger, and switches over to 20v (unless I plug a battery in, then it doesn't switch and stays at 5v). Not sure this if the battery issue is relevant to not booting though as battery does not appear to charge, so could just be a faulty battery.

    Right after negotiation happens from 5v to 20v, board draws around 180 - 250mA, then settles between 30 and 45mA thereafter where it stays.

    The main issue as I see it is that PP3V3_S5 is missing, so boot sequence can't proceed.

    Machine is able to go into DFU mode, but I have tried both revive, and restore many times with no luck. Both fail with an error 4014 something along the lines of the machine being forced in DFU mode.

    I have not found any rails shorted to ground as of yet. I have refloated (not reballed) U7800, and a brief warming of the T2 chip with flux to see if that helped things along, but made no difference except for a slight current draw increase while the T2 chip was hot.

    Measured Voltages:
    PPBUS_G3H: 12.6v
    PP3v3_G3H: 3.29v
    PP1V8_SLPS2R: 1.8v
    PP3V_G3H: 2.99v
    LDO_CORE: 1.49v
    LDO_RTC: 1.49v
    PMU_VPUMP: 4.97v
    PP1v1_SLPS2SR: 1.1v
    PP1V8_SLPS2R: 1.8v
    PP3V3_G3H_RTC: 3.29v
    PMU_LDO3_OUT: 1.79v
    P1V8G3S_EN: 1.8v
    P1V8_G3S: 1.79v
    P5VG3S_EN: 3.29v
    P5VG3S_PGOOD: 1.78v
    PMU_ACTIVE_READY: 1.791v

    P3V3G3S_EN: 0v
    P3V3_GS: 0v
    PP3v3_S5: 0v

    PP3V3_AWAKE: 3.29v
    All other _AWAKE values match their respective voltages

    PP3V3_S5 resistance to ground: 86.6k ohm.
    PP3V3_S5 diode reading to ground: 0.353v


    All PM_SLP_Sx_L values pulse when turning on, but I am not able to see what voltage they are pulsing to (I don't have a scope)

    As you can see from the above voltages, based on the schematic page 63, all of the inputs relevant to PP3V3_S5 to U7800 are present, and all outputs are there except PP3V3_S5 and PD_HIO_PWR_EN.

    Is it safe to assume that the issue here is the PMIC (U7800)? Are there any other tests I can use to confirm that it isn't CPU, T2, or NAND failure? Any other measuremants that I can take to confirm even further that the issue is U7800?

    All help appreciated.

    Thanks in advance!
  • mon2
    Badcaps Legend
    • Dec 2019
    • 14030
    • Canada

    #2
    Re: 820-01958 - Missing PP3V3_S5 - No liquid damage

    Error 4014

    https://logi.wiki/index.php/DFU_Mode_Restore_(Macs)

    Comment

    • duwane
      Senior Member
      • Mar 2022
      • 55
      • New Zealand

      #3
      Re: 820-01958 - Missing PP3V3_S5 - No liquid damage

      Quick update for anyone coming to this in the future. I ended up fixing this device. Corrupt firmware was stopping PP3V3_S5 from being produced by the PMIC.

      I was getting DFU failure error 4014 when trying to revive or restore the machine from a host laptop running Catalina using a USB-A to USB-C cable.

      I tried several cables, but all failed with the same error. I was about to give up, but tried one last thing. I then ran Apple Configurator 2 on a machine running Monterey, and used a usb-c to usb-c cable, and the revive finished successfully!

      So the moral of the story is, don't believe what it says in the Apple article about how to do a DFU being able to use any machine as a host as long as its running macOS 10.15.6 or later. Use a machine running the latest version, and it seems to be more successful than using an older macOS version.

      Comment

      • zaratustrax
        New Member
        • Aug 2015
        • 9
        • mexico

        #4
        I tried with a Monterrey and Apple configurator says it needs Sonoma

        Comment

        • mon2
          Badcaps Legend
          • Dec 2019
          • 14030
          • Canada

          #5
          We purchased a relatively current unit to do the same and run Sonoma.

          Comment

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