820-00165 No brains, no chime. BIOS CS comparisson

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  • zpi
    Senior Member
    • Feb 2018
    • 132
    • Lithuania
    #1

    820-00165 No brains, no chime. BIOS CS comparisson

    Hi guys, so i have 820-00165 with no brain here. Powering on sequince looks like this:

    DCIN jack in -> 14second 0.4amp -> restart -> 0.4amp allways on no chime.

    Working board looks like this

    MagSafe in -> 0.54amps ->0.30amps ->chime

    My board bios CS activity: DSCN1077.jpg
    Working board CS activity: DSCN1076.jpg

    Looks like its only first pulses of bios activity, maybe thoughts what can cause this? Tryed to switch bioses between boards, same thing happens, so we can rule out bad bios. Termination resistors and vias cheked. Do i have bad PCH ?

    Piernov, what are your thoughts ?
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    • zpi
      Senior Member
      • Feb 2018
      • 132
      • Lithuania
      #2
      Re: 820-00165 No brains, no chime. BIOS CS comparisson

      Update:

      Replaced SMC between these boards, no effect, conclusion SMC good.
      Reacts to SMC Bypass, max fan, no chime.

      Does not react to PRAM reset.
      Last edited by zpi; 01-19-2021, 04:15 PM.

        Comment

        • reformatt
          Badcaps Legend
          • Feb 2020
          • 1408
          • Australia
          #3
          Re: 820-00165 No brains, no chime. BIOS CS comparisson

          I have the same fault on a liquid damaged Apple refurb board. I feel dread everytime I see FRU on a 820-00165 that comes in for repair.

          So original fault was corrosion at the bottom of U7501. So after attending to that I ended up with a powered board, but no boot. At the time troubleshooting I was probing around the EFI chip and the board booted. So I took it off, flashed it with clean ME etc and was all working. Left it running for days and threw it on the shelf.

          So customer comes to pick it up 4 weeks later, and its not booting. Drawing 400ma and thats it. So I get the flurry of activity on the U6100 initially, but no loading there after. I did measure out connectivity on the termination resistors to the CPU, but no issues there.

          Basically getting to RAM initialization in the boot seq and no further. No beeps though. There was some corrosion I had missed between U2500/U2600 on C2403/C2405. This is the PP1V2_S3 rail that goes directly under the RAM. I reflowed these two RAM chips to no effect. So at this point I'm leaning to having to pull off the RAM and reball it, but..meh, it's going to the donor bin.

            Comment

            • mcplslg123
              Badcaps Legend
              • Jun 2015
              • 7262
              • india
              #4
              Re: 820-00165 No brains, no chime. BIOS CS comparisson

              This logic boards SPI termination resistors get corroded. Look carefully under microscope for any rotten trace.

                Comment

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