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820-3787-A Short on PPBUS_G3H

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  • 820-3787-A Short on PPBUS_G3H

    I have removed F7140 and F7141 and the short is on the TO SYSTEM line.

    What would be the next step? To inject 1V and 500mA to PPBUS_G3H?

  • #2
    Yes inject 1 volt into PPBUS and see what gets hot. Remove CPU heatsink to make sure it's not the CPU.


    • #3
      "To inject 1V and 500mA to PPBUS_G3H?"
      How do you think to inject exact current for an exact voltage???
      The current depends by injected tension and resistance to ground on that rail

      First of all, what is the exact value of that short?
      Next check for any big coil with the same value.
      This way you can find a shorted high-side MOSFET.
      NEVER inject tension before!!!

      If all MOSFETs OK, then start with 1V and go up, just maintain the current bellow the ampers limit of your bench power supply.


      • #4
        Excuse me, my bad. I didn't express myself right.

        1V with 500mA is 1V set with 500mA as a limit for current on my power supply. It depends on the device itself, resistance on that rail, how much it will draw.

        The exact value of the short is 0 Ohms.

        On to the hunt for big coils with the same value then...


        • #5
          Always set current limit at max when inject.
          The power rail in question will take the current accordingly with voltage and ressitance to ground.
          This is the reason to start with low voltage, that bench power supply do not reach amps limit instantly...


          • #6
            So it is safe to put 5A (which is what DCPS can be set at) with, for example, 3V and let it flow through PPBUS_G3H without damaging CPU?

            I'm going through coils with multimeter and resistance mode now, didn't inject any power yet.

            Note: when the adapter is connected (only once I did it), C7333 was burning at 100C. Yet it looks good, with glue on top of it.


            • #7
              If none of high-side MOSFETs for CPU is shorted, why would the current flow through the CPU???
              And don't start with 3V.
              If the rail tries to sink more than 5A (e.g. 3V/0.5ohm=6A), then the bench power supply will not inject at all; as it will enter in protection mode instantly.


              • #8
                There's still so much to learn. Okay.

                So none of the big coils had odd values. I took a look at C7333 from the side and to my surprise, it did have a slight crack. I removed it, PPBUS_G3H measures 0.8MOhms.

                Is it safe to attach the charger to see if the fans spin or shall I first replace C7333 and then connect charger?


                • #9
                  Board should start without it.
                  But I recommend to solder it; its rol on the board is important.

                  "PPBUS_G3H measures 0.8MOhms"
                  Always use diode mode, red probe to ground.
                  Only switch to ohm mode in case of very low values...


                  • #10
                    If that was the short, then you're good should work now. Best to replace the cap, but it will work without it


                    • #11
                      I have replaced the cap and laptop works fine. Mark as solved, please.

                      Onto the next one...


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