A1466 820-3437-B 10 second fan off on

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  • test_guy2010
    New Member
    • Jul 2018
    • 3
    • Australia
    #1

    A1466 820-3437-B 10 second fan off on

    Hello, I have a MacBook board that I am stuck on.

    This is a 820-3437-B board which I know the standard turn on procedure is 3 fan spins before powering up and staying on, however this board the fan turns on for about 10 seconds, turns off, then turns on and stays on until powered off.

    This board did appear to have some liquid near U1900 (clock chip) which I have replaced as well as the crystal just to make sure.

    I get all voltage rails, vCore stable at about 1.7v, very little heat coming from the CPU/PCH (mostly PCH), with a USB with a bootable system the light flashes indicating the PCH should be working.

    However it is failing to boot through as well as the strange starting behaviour.

    Odd things I have found are U3900 (camera processor) was heating up quite a bit so was taken off the board, should be able to boot without it, just missing camera functions, signal PCH_INTVRMEN is 2.6v and PCH_INTRUDER_L is 1.6v.

    I am unsure where to go from here so asking for advice, thanks.
    Tags: None
    • reformatt
      Badcaps Legend
      • Feb 2020
      • 1399
      • Australia
      #2
      Re: A1466 820-3437-B 10 second fan off on

      Check U8005 for corrosion (can be hard to spot). Seen something similar...was corrosion under pin 1.

      If that fails, flash a known working clean ME BIOS to U6100 and check all termination resistors. Are you getting a chime/display etc?

        Comment

        • test_guy2010
          New Member
          • Jul 2018
          • 3
          • Australia
          #3
          Re: A1466 820-3437-B 10 second fan off on

          No good, nothing around U8005 took it off and checked.
          Flashed a clean BIOS to the chip, resistors are fine.

          No display or chime, just the 10 second fan spin, off then back on and stays spinning.

          For now this will have to be a fail as it's been a time sink for me.

            Comment

            • reformatt
              Badcaps Legend
              • Feb 2020
              • 1399
              • Australia
              #4
              Re: A1466 820-3437-B 10 second fan off on

              Pull off the edge bonding and reflow the SMC with plenty of flux. Usually crap underneath it with weird behaviour. Also check PCH resistance to ground for PP1V05 rail. Under 100 ohm is usually damaged PCH from messed up converter feedback.

                Comment

                • Instafixx
                  Badcaps Veteran
                  • Jul 2022
                  • 374
                  • India
                  #5
                  Re: A1466 820-3437-B 10 second fan off on

                  Originally posted by reformatt
                  Pull off the edge bonding and reflow the SMC with plenty of flux. Usually crap underneath it with weird behaviour. Also check PCH resistance to ground for PP1V05 rail. Under 100 ohm is usually damaged PCH from messed up converter feedback.
                  Hi, i have the exact same issue. Wonder if this was solved. In my case if we probe the SMC_RESET_L anyhwhere on the board, the Fan Spin stops.

                  U8005 Pin #1 shows 5V.

                    Comment

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