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LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

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    LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

    Hello,

    I've mentioned computer sitting on my desk and driving me nuts


    This device came in for screen replacement and I did it like always;

    disconnect battery, replaced the screen, device won't power up anymore

    No Power/Charging indicator LED is glowing, no fan spin and no other sign of life.

    +5VALW is working but +3VALW has a short to ground which sits between the PJ401 and PJ601. Also PU401 is getting quite hot but I think the fault lies in another part.

    I assume that the ENE KB9012 or the CPU has some damage but they look fine and I don't know how to proof my assumption so if any one is here who can help I would be pleased
    Also I wouldn't reject a Boardview file for this device but as far as I know this isn't available.

    Thanks in advance and stay healthy 😷😬

    Schematics: LA-A921P Schematic

    #2
    Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

    PU401 will heat up if it's trying to supply too much current due to a short to ground on +3VALW (or +3VL). If you disconnect PJ401 PU401 should not heat up anymore as it's been isolated from the short to ground. After disconnecting PJ401 you can also confirm the short is indeed on +3VALW and not +3VALWP.

    In any case fastest way to isolate the problem is to inject 3V into +3VALW and check if PCH die (small die on CPU package) is heating up, or the EC.
    OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

    Comment


      #3
      Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

      Hi Piernov,

      thanks for your fast answer.

      The funny part is that PU401 is heating up even if PJ401 is disconnected. It's not super hot and touchable. I pulled the PU401 and tested some puns like LX which goes to +3VALWP and then over PJ401 to +3VALW and there is no short. Only if I connect the PJ401.

      I'll try this injecting method. Thank you very much.

      Comment


        #4
        Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

        i think thats a cpu issues ...just encountered the issue exactly as you described

        Comment


          #5
          Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

          Originally posted by lctrbrt View Post
          Hi Piernov,

          thanks for your fast answer.

          The funny part is that PU401 is heating up even if PJ401 is disconnected. It's not super hot and touchable. I pulled the PU401 and tested some puns like LX which goes to +3VALWP and then over PJ401 to +3VALW and there is no short. Only if I connect the PJ401.

          I'll try this injecting method. Thank you very much.
          \
          resistance on +3VLP ?

          Comment


            #6
            Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

            Originally posted by piernov View Post
            In any case fastest way to isolate the problem is to inject 3V into +3VALW and check if PCH die (small die on CPU package) is heating up, or the EC.
            Thanks for this, I had the same issue on an LA-A342P board. Unfortunately, the PCH heats up and the board is now scrap

            Comment


              #7
              Re: LA-A921P (Lenovo Yoga 2 13) +3VALW short2ground

              12v mosfet burn and solution with drill pcb
              Attached Files

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