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A1989 820-00850 logic board does not complete start

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    A1989 820-00850 logic board does not complete start

    Hi,

    1. I have macbook pro 2018 with T2 chip here which is not starting.

    2. The board has none psychical damage, no liquid damage, looks like brand new.

    3. I bought this macbook, previous owner said that macbook suddenly stopped working and did not turn on again.

    4. I successfully restored it through DFU with apple configurator 2 and other macbook.

    5. When I apply a power, the system will spins the fans for second and then after approx 30 seconds again.

    6. No display at all, no startup chime. I have a trackpad click.

    7. I measured important power rails, which look fine.

    8. ALL_SYS_PWRGD is 1.8V exactly.

    9. The PPVCC_S0_CPU will go to 0.88V for time the fans are spinning and then 0V.

    10. Sometimes (1 try out of 10), the PPVCC_S0_CPU will stay at 0.75V with fans spinning.

    Please advise me, what should I check next.
    Last edited by tony42; 07-13-2021, 12:25 AM.

    #2
    Re: A1989 820-00850 logic board does not complete start

    I studied a1989 schematics little bit,

    I can assume, if I have all_sys_pwrgd signal ok, there will be problem either with U7100 or U7210, U7220, U7270, U7410, U7420, U7430.

    It can be also bad CPU.

    So I need to check all components around these IOs, measure some voltages and will post here.


    Please correct me if I am wrong.

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      #3
      Re: A1989 820-00850 logic board does not complete start

      Review this video which may help.

      https://www.youtube.com/watch?v=UcFkOX4PJHM

      Comment


        #4
        Re: A1989 820-00850 logic board does not complete start

        Hi, Tony
        I have run into the same problem. Did you find the solution?

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