820-00850-A Boot Looping

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  • tonylock
    Member
    • Jul 2014
    • 10
    • Spain

    #1

    820-00850-A Boot Looping

    Hi,

    A customer brought in an A1989 logic board that is in a boot loop.
    It chimes and the backlight flashes briefly and does it all over again. The CPU gets warm as do the SSD, U2800 and UB00. It let me rebuild bridge OS sucesfully in DFU mode with no change.

    All USB ports get 20v and go up to 0.456ma and then down again in the loop.

    The board is clean, there are no signs of liquid damage or corrosion. The customer said it just wouln't start one day for no reason.

    Some of the voltages I checked are as follows:

    PP3V3_G3H - 3.35v
    PP5V_G3S - 5.12v
    PVCCEDRAM_S0_REG_R - 0v
    PPVCCGT_CPU_PH3 - 0v
    PPVCCGT_CPU_PH2 - 0v
    PPVCCGT_CPU_PH1 - 0v
    PPVCC_CPU_PH1 - 0.656v
    PPVCC_CPU_PH2 - 0.655v
    PPVCCSA_CPU_R - 0.813v
    PP0V95_S0_CPUVCCIO_REG_R - 0.953v
    PP1V2_S3_REG_R - 1.2v
    PPVIN_S0SW_LCDBKLT - 0.012v
    P5VUSBC_T_R - 0v
    P5VUSBC_X_R - 0v
    PP0V9_SSD0 - 0.899v
    PP1V8_SSD0 - 1.799v
    PP2V7_NAND_SSD0 - 2.5v
    ALL_SYS_PWRGD - 1.7v

    Any advise would be a great help.
  • TechSplendid
    Member
    • Oct 2023
    • 14
    • Gelderland

    #2
    Did you ever find out what the problem was? I seem to have the exact same thing.

    Comment

    • mon2
      Badcaps Legend
      • Dec 2019
      • 13940
      • Canada

      #3
      Carefully measure the voltage to ground of the battery connector. Check the smbus scl & sda line voltage.

      Comment

      • Problematic G3nius
        New Member
        • Jun 2024
        • 2
        • United States

        #4
        I also have a device that I'm working on that has this same issue. It attempts to boot pulls about 19 watts then shuts off. The device came in with an aftermarket battery, Iswapped it for a known good one but still the same issue persist. Any suggestions?

        Comment

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