A1466 / 820-3437-B / only starts on the 3rd attempt

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  • GfilipeZ
    Member
    • May 2021
    • 43
    • Portugal
    #1

    A1466 / 820-3437-B / only starts on the 3rd attempt

    Hi,

    I'm trying to detect a strange anomaly that keeps repeating itself in the same way.
    If i press the power button, the fan spins 1/4 and stops. I press the button again, and the fan spins normaly, but there is no boot. Then i force it to shutdown, and press the button for the 3r time, and the machine boots normaly.

    If i let the macbook turned off for about 20/30 min, the anomaly comes again, and i have to do all again to make it boots.

    I already tried an SMC from a donor logic board and dump a clean firmware to the EFI ic, but the problem always remains the same.

    Has anyone experienced a similar problem?

    Best regards.
    Tags: None
    • GfilipeZ
      Member
      • May 2021
      • 43
      • Portugal
      #2
      Re: A1466 / 820-3437-B / only starts on the 3rd attempt

      Originally posted by GfilipeZ
      Hi,

      I'm trying to detect a strange anomaly that keeps repeating itself in the same way.
      If i press the power button, the fan spins 1/4 and stops. I press the button again, and the fan spins normaly, but there is no boot. Then i force it to shutdown, and press the button for the 3r time, and the machine boots normaly.

      If i let the macbook turned off for about 20/30 min, the anomaly comes again, and i have to do all again to make it boots.

      I already tried an SMC from a donor logic board and dump a clean firmware to the EFI ic, but the problem always remains the same.

      Has anyone experienced a similar problem?

      Best regards.

      Hi,

      Any idea?

        Comment

        • reformatt
          Badcaps Legend
          • Feb 2020
          • 1400
          • Australia
          #3
          Re: A1466 / 820-3437-B / only starts on the 3rd attempt

          Check for presence of PP3V3_S5_AVREF_SMC. If it's missing, usually a shorted cap next to the SMC. If this is missing, board will only start in SMC Bypass mode which sounds like what you are doing.

            Comment

            • GfilipeZ
              Member
              • May 2021
              • 43
              • Portugal
              #4
              Re: A1466 / 820-3437-B / only starts on the 3rd attempt

              Originally posted by GfilipeZ
              Hi,

              I'm trying to detect a strange anomaly that keeps repeating itself in the same way.
              If i press the power button, the fan spins 1/4 and stops. I press the button again, and the fan spins normaly, but there is no boot. Then i force it to shutdown, and press the button for the 3r time, and the machine boots normaly.

              If i let the macbook turned off for about 20/30 min, the anomaly comes again, and i have to do all again to make it boots.

              I already tried an SMC from a donor logic board and dump a clean firmware to the EFI ic, but the problem always remains the same.

              Has anyone experienced a similar problem?

              Best regards.
              I dumped another file with clean firmware to the EFI ic, and restored the Mac OS. Don't ask me how, but, solved my problem.

              Thanks guys.

                Comment

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