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820-3476 green light, no boot. Weird 5V rail behaviour

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  • 820-3476 green light, no boot. Weird 5V rail behaviour

    Have an 820-3476 with green light. I think it had liquid damage initially but someone else has already messed with the board so i can't really tell

    It has green light. Have started going down the power rail list. everything looks normal and i've stopped at the 5v rails because they are acting strange. Evertime I measure it's a different number. Sometimes it's 0, sometimes it's 2.5 and sometimes it's 5. I don't see it change when i'm holding the probes on it but when i release the probes and put them back on it's a different number again.

    The thing I see that has definitely been messed with is
    u7501

    Shall i keep going down the power rail list or am i on the right track?

    Thanks!

  • #2
    If PP5v_S5 is pulsing, it could very well be from a poorly soldered or bad TPS51980.

    Comment


    • #3
      Post exact voltage for PPBUS_G3H.
      Also post some voltages for U7501, pins 23, 13, 22, 29, 12, 21, 4.
      Stable 3V42 power rail?

      Comment


      • #4
        PPbus is 12.58v

        U7501
        pin 23 is 12.58
        pin 13 is pulsing between 0 and 2v
        pin 22 is 3.3v
        pin 29 is is sometimes 0, 2.5 and 5
        pin 12 pulsing between 0 and 3.3
        pin 21 pulsing between 0 and 3.4
        pin 4 0v

        3v42 is stable at 3.4v

        Comment


        • #5
          So SMC_PM_G2_EN is not stable; or SMC detects a problem and pull it down.
          Try to start in SMC bypass mode first.
          Check if SMC_RESET_L is stable.

          Comment


          • #6
            is SMC bypass where i have to run a wire to ground repeatedly? How do I do that? thanks!

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            • #7
              ok, have tried smc bypass mode, doesn't work

              Comment


              • #8
                Press power button, connect charger and maintain pressing 5-10s...

                Comment


                • #9
                  thank you,tried it on this one and nothing

                  Comment


                  • #10
                    "Check if SMC_RESET_L is stable."
                    ???

                    Check for pulse at least on the coils...

                    Comment

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