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    #1

    A2159 will not boot past Apple Logo

    Hi Everyone. I have a Mac for a topcase replacement. I have completed the job however the Mac will boot and I get the startup chimes but not pass the Apple Logo, not even a progress bar. After a few seconds the fan spins fast. The board is 820-01598-A. I have disconnected everything except the USB ports and display and the issue persists. I am drawing 20.42v and .461A with just the screen connected so it looks like it is booting. I have looked over the board with a scope and I do not see anything that appears wrong. I can not get into diagnostics, NVRAM reset or DFU. The only issue is the topcase is used, but excellent condition however the Trackpad cable was damaged on the connector and stupidly I did not notice until I tried to connect it. I had not power or battery attached atthe time of course and the connector on the Logicboard is perfect. if anyone has any ideas that would be good and I appreciate your help.
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  • Answer selected by Logix_UK at 10-17-2024, 06:16 AM.
    Originally posted by reformatt View Post
    Touchbar would be my first suspect.
    Hi, thank you however the issue happens even if the touchbar is not connected.
    • Selected Answer

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      #2
      Touchbar would be my first suspect.

      Comment

        #3
        Originally posted by reformatt View Post
        Touchbar would be my first suspect.
        Hi, thank you however the issue happens even if the touchbar is not connected.
        • Selected Answer

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          #4
          Review the trackpad and trackpad cabling. Be sure the trackpad cable contact pitch is suitable for this model's connector. There are sensors in the trackpad assembly that must be visible during the OS boot using smbus communication. If absent, there will be a high fan spin.

          Measure the voltage to ground of each smbus pin on the trackpad cable.

          Respectively, the trackpad must be connected and working to boot.

          Comment

            #5
            Originally posted by mon2 View Post
            Review the trackpad and trackpad cabling. Be sure the trackpad cable contact pitch is suitable for this model's connector. There are sensors in the trackpad assembly that must be visible during the OS boot using smbus communication. If absent, there will be a high fan spin.

            Measure the voltage to ground of each smbus pin on the trackpad cable.

            Respectively, the trackpad must be connected and working to boot.
            OK thank you, I have replaced the trackpad cable and reassembled and it now boots, thank you all for your support. Great forum, great techs

            Comment

              #6
              Out of curisoity, what is the relation between the trackpad cable and stuck Apple logo. Whats happening behind the scene?

              Comment

                #7
                This reminds me of a very involved case with XMOS (UK) Semiconductor (multicore processors - mainly for audio when we were considering it for new designs). Long winded story but is as follows. The multicore processor would emulate the USB handshakes using 'bit banged code' to offer a USB audio device. Respectively, USB is a very time sensitive interface. If too much time is invested in one core vs. another, the USB interface will suffer and die. The other cores were handling the audio processing. A large audio OEM company invested almost 9 months I was told on attempting to fix this failed new audio design - attempting numerous new PCB layouts, etc. Then they sent in the latest design to us for a review. After a review of the firmware, the root cause was...drumroll...a missing I2C / SMBUS slave device. The code loop was repeatedly attempting to ping a SMBUS slave node that was absent on THEIR design but was on the reference board design from the factory. While stuck in this phantom device hunt loop, the USB interface would suffer and would die over time.

                Same case here with the trackpad. The sensors are low cost I2C / SMBUS nodes that must be found or enumerated by the logic board else the logic board assumes the worst and believes that the CPU temp is out of range so blast the fan into hyper speed and throttle the CPU speed.
                • Likes 1

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                • SMDFlea
                  #7.1
                  SMDFlea commented
                  10-18-2024, 03:27 AM
                  Editing a comment
                  Its a good explanation of the fault, nice.
                #8
                Originally posted by Axis937 View Post
                Out of curisoity, what is the relation between the trackpad cable and stuck Apple logo. Whats happening behind the scene?
                The job was a topcase replacement. I sourced a used by good condition topcase but as I was re assembling I noticed the track pad cable was damaged, see attached. I put the Mac back together minus the trackpad and it would not boot. I did not realise that the trackpad needed to be connected until mon2 told me. As soon as I replaced the trackpad cable it booted.
                Attached Files

                Comment

                  #9
                  mon2 Thank you for your help and the explanation.

                  Comment

                    #10
                    Originally posted by mon2 View Post
                    This reminds me of a very involved case with XMOS (UK) Semiconductor (multicore processors - mainly for audio when we were considering it for new designs). Long winded story but is as follows. The multicore processor would emulate the USB handshakes using 'bit banged code' to offer a USB audio device. Respectively, USB is a very time sensitive interface. If too much time is invested in one core vs. another, the USB interface will suffer and die. The other cores were handling the audio processing. A large audio OEM company invested almost 9 months I was told on attempting to fix this failed new audio design - attempting numerous new PCB layouts, etc. Then they sent in the latest design to us for a review. After a review of the firmware, the root cause was...drumroll...a missing I2C / SMBUS slave device. The code loop was repeatedly attempting to ping a SMBUS slave node that was absent on THEIR design but was on the reference board design from the factory. While stuck in this phantom device hunt loop, the USB interface would suffer and would die over time.

                    Same case here with the trackpad. The sensors are low cost I2C / SMBUS nodes that must be found or enumerated by the logic board else the logic board assumes the worst and believes that the CPU temp is out of range so blast the fan into hyper speed and throttle the CPU speed.
                    WOW!!! i bet no one would have thought about this.

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