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Dell XPS 9365 2-in-1 LA-D781P "No bootable device" and low VCC_CORE

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    #1

    Dell XPS 9365 2-in-1 LA-D781P "No bootable device" and low VCC_CORE

    Hello,
    currently I'm tinkering with above mentioned broken device. It started with a shorted PD controller. I replaced it and have an open topic on this forum on reprogramming it.
    Currently I'm powering it with a bench supply soldered to the battery connector (laptop battery is dead).
    This way the device is booting into BIOS and Diagnose mode fine. But when I try to restore the factory image during diagnose the laptop always greets me with "no bootable device".

    Looking at the bios the ssd is recognized (shown with type and size in some storage menu). But it does not appear in the boot priority list. Neither in UEFI nor LEGACY mode.
    So I wanted to give bios update a try. But it always stated "insufficent power". On cord as well as on "battery"(bench supply at 8.8V).
    This led me to measure voltages on all inductors and map it to system voltages according to the schematics.
    This way I found out that VCC_CORE voltage is only around 0.65 V and no VCC_GT voltage is present. According to the schematic both should be at around 1.5 V. VCC_GT only comes up once VCC_CORE is good.

    Both are generated from PU801 ISL95852. So I ordered a replacement and just installed it. Exactly the same behavior as before.

    I checked the board with a thermal cam to see where my voltage drops unintended. But nothing sticks out.
    Any suggestions what to look for? Came across "Clean BIOS ME region" topics a lot. Could this help in this case?
    Tags: None
  • Answer selected by groomit at 10-31-2024, 02:56 PM.
    Originally posted by ademircps View Post
    Hello friend.

    I have a board here, I made some measurements for you. Hope this helps you
    Wow, thanks a lot for taking the time. Your measurements support my latest observations.

    I learned that VCC_CORE voltage is variable and depends on the CPU load.
    Also VCC_GT doesn't have to be present all the time. This is supported by your VCC_GT measurement.

    Turns out VCC_GT was a red herring. I swapped the SSD with a known working one with Win 10 installed and it booted just fine.

    Still some things to figure out (but probably in a new thread):
    - Left USB-C is supplying the laptop only when my USB-Meter is in-between.
    - Right USB-C only negotiating 5V. But that is probably related to PD Controller programming mentioned in the first post of the thread.
    - Crackling noise from the speakers without audio being played.
    - Battery dead and not charging
    • Selected Answer

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      #2
      Cleaning the ME Region did not help. Laptop comes on and diagnose-mode runs fine. So I assume I haven't f*cked the BIOS flash.
      Still VCC_CORE is at 0.65 V. What I noticed: Upon Boot VCC_CORE goes up to 0.8 V for a short period of time and then drops to 0.65 V and stays there.
      VCC_GT still at 0 V.

      Any tips what to look out for?

      Comment

        #3
        Hello friend.

        I have a board here, I made some measurements for you. Hope this helps you
        Attached Files

        Comment

          #4
          Originally posted by ademircps View Post
          Hello friend.

          I have a board here, I made some measurements for you. Hope this helps you
          Wow, thanks a lot for taking the time. Your measurements support my latest observations.

          I learned that VCC_CORE voltage is variable and depends on the CPU load.
          Also VCC_GT doesn't have to be present all the time. This is supported by your VCC_GT measurement.

          Turns out VCC_GT was a red herring. I swapped the SSD with a known working one with Win 10 installed and it booted just fine.

          Still some things to figure out (but probably in a new thread):
          - Left USB-C is supplying the laptop only when my USB-Meter is in-between.
          - Right USB-C only negotiating 5V. But that is probably related to PD Controller programming mentioned in the first post of the thread.
          - Crackling noise from the speakers without audio being played.
          - Battery dead and not charging
          • Selected Answer

          Comment

            #5
            I'm glad you managed to solve the Windows boot problem.
            I hope you are successful in resolving the remaining problems.

            I bought the one I have here with a defect so I could restore it and reselling it, it came without NVME.
            There was a problem with the ISL95852, it was cold solder, now it's working.


            Sorry for my writing, it's all via google translator, I hope you understand.

            Comment

              #6
              I can understand you just fine. Congrats for spotting the issue.
              My motivation was the same: buy - repair - resell.
              But as the SSD is bad and the battery too, it is almost not economical to do. Will probably keep it as I always wanted a convertible.

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