Macbook A1286 no boot, voltages seem ok

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  • retrorepair2
    Senior Member
    • Feb 2023
    • 75
    • United Kingdom
    #1

    Macbook A1286 no boot, voltages seem ok

    This board is a head scratcher.

    I've checked all voltages against the schematic and all are present on powerup, but get no chime, taking ram out doesn't give me beeps, sleep light and fans come on for about 5 seconds then shuts down.

    What I'm reading is pointing to the gpu but this is a 820-2850 and I didn't think this revision suffered this badly from this issue? I've already replaced C9560 but same issue.

    Not really keen to run loads of wires just yet to disable the gpu, is there anything I can do to rule the gpu out?
    Tags: None
    • mon2
      Badcaps Legend
      • Dec 2019
      • 13897
      • Canada
      #2
      Re: Macbook A1286 no boot, voltages seem ok

      What is the voltage to ground of ppbus_g3h?

        Comment

        • retrorepair2
          Senior Member
          • Feb 2023
          • 75
          • United Kingdom
          #3
          Re: Macbook A1286 no boot, voltages seem ok

          It's on battery as I don't have a charger at the moment, but it's 11.28v when power is off, 10.8v when it's on.

          Also checked ALL_SYD_PWRGD and it's 3.3v when powered on so sounds like it's happy enough with power.

            Comment

            • retrorepair2
              Senior Member
              • Feb 2023
              • 75
              • United Kingdom
              #4
              Re: Macbook A1286 no boot, voltages seem ok

              I've noticed PPVCORE_GPU is about 3ohm to GND, surely can't be right??

              It does read .9v which is in spec according to the schematic..

                Comment

                • retrorepair2
                  Senior Member
                  • Feb 2023
                  • 75
                  • United Kingdom
                  #5
                  Re: Macbook A1286 no boot, voltages seem ok

                  Further testing: There is no USB activity on my thumb drive and LCD_PWR_EN does go low. I'm starting to wonder if the GPU is the only factor left

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