Macbook Air A1370 820-3024 CPU init and VCore missing

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  • EdwardGeo
    Senior Member
    • Mar 2020
    • 109
    • Ukraine
    #1

    Macbook Air A1370 820-3024 CPU init and VCore missing

    All voltages are okay, even a thunderbolt boost is reacting on power request by cortex. Spi rom is read by pch, All_system_is_okay (mean the signal 3.3v by smc is present). But CPU won't request voltage from Max buck converter to power up VCore voltages to start the CPU. CPU and pch is getting warm. So there is no SVID and SVCLK data exchange. A lot of info on the web declare the TON signal failure on 2 pin of Max controller, and it has 90.2K, the voltage drop on power on, down to 0.35v. whrlen the system is off, then voltage on pin 2 is 8.4 volts.

    Btw forgot to say, all voltages are in place, so without reading SVID or SVCLK, system looks like halted, fans are spinning, USB are powered. Tried to use another rom dump, but no difference.

    Any ideas? Because of missing MAXIM controller datasheet, I can't get idea of principal of how it's working
    Last edited by EdwardGeo; 06-07-2023, 03:12 AM.
    Tags: None
    • EdwardGeo
      Senior Member
      • Mar 2020
      • 109
      • Ukraine
      #2
      Re: Macbook Air A1370 820-3024 CPU init and VCore missing

      Probing MAX15092G
      Attached Files

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        • EdwardGeo
          Senior Member
          • Mar 2020
          • 109
          • Ukraine
          #3
          Re: Macbook Air A1370 820-3024 CPU init and VCore missing

          I have compared MAX probing with one of a donor boards, and here are the results:

          it seems, like MAX isn`t actually talking to CPU to powerON it. it will set 1.2v right after it will be enabled and only 2-4 seconds, it will set cpu voltages to levels are needed. But on Macbook Air A1370 this voltages are missing. So rather MAX is need to be replaced, or something isnt enabling Max controller
          Attached Files

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            • EdwardGeo
              Senior Member
              • Mar 2020
              • 109
              • Ukraine
              #4
              Re: Macbook Air A1370 820-3024 CPU init and VCore missing

              Finally: desolder coil on cpu power rail, and all voltages appears. Buck was switching to overload protection. After coil was removed, the cpu rail showed 15 ohm resistance, when hot=9.8 ohm to ground, while the donor board with same cpu has 27 ohm.

              Solution: cpu replacement. On Apple devices that is extremely hard, because of missing marking and a lot of compound on cpU.

                Comment

                • EdwardGeo
                  Senior Member
                  • Mar 2020
                  • 109
                  • Ukraine
                  #5
                  Re: Macbook Air A1370 820-3024 CPU init and VCore missing

                  Desolder donor board CPU, nice that no epoxy was under CPU, easy to desolder. Waiting for stencil. Hope it will work. CPU isn't supported by config. So i7 CPU from MBA13" to MBA11". Maybe Bios modding is required.
                  Attached Files

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