No short but PPBUS_G3H missing 820-01700

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  • Comp_Pro
    Member
    • Jun 2020
    • 33
    • USA
    #1

    No short but PPBUS_G3H missing 820-01700

    Hello all,

    I have this 820-01700 board which came in with 5V 0.015A on the ammeter. Ammeter cycles every 5 seconds or so. Upon inspection I found PPBUS_G3H is reading around 0.6V. There is no short to ground. Diode mode reading is about 0.420V. When I remove fuses F7000 and F7001 the U700 side of the circuit produces 12.3V and the cycling goes away on the ammeter but still stays at 5V and now reads 0A. This goes away as soon as I put back the fuses. I tried injecting voltage onto the system side of the fuse pads but I do not get any current draw at all. I tried seeing if the voltage I was injecting would show up on any of the CPU inductors but it does not.


    PP2V5_NAND_SSD0 read about 0.068 diode mode to ground on one occasion but then went back to reading 0.340
    PP0V9_SSD0 reads 0.337
    PP1V8_SSD0​ reads about 0.340

    Any other things I could check? Very tricky issue since I can't seem to get a reading on whatever short there is or appears to be. I read a similar post where someone suggested checking DFU but would that actually be an option considering we don't even have PPBUS_G3H? Would that be worth looking into?
    Tags: None
    • mon2
      Badcaps Legend
      • Dec 2019
      • 14172
      • Canada
      #2
      Flux and remove C9586. Then test again with the fuse installed.

        Comment

        • Comp_Pro
          Member
          • Jun 2020
          • 33
          • USA
          #3
          Figured out the issue.

          I noticed that when I powered it on this morning I briefly got 20V but was stuck at low current, current was 30mA IIRC. This was after removing C9586 but the capacitor was not shorted and didn't seem to be the cause of the change in behavior. While the charger was still giving me 20V i measured PPBUS_G3H and found it was at 12.3V. After a short while I lost 20V at the USB-C port again and it went back to 5V and cycling. The issue appeared to be related to temperature. Even though I did not get back 5V the ammeter would stop cycling if I warmed up the board. I measured PPBUS_G3H again and found that the voltage here was varying anywhere between 0.6V to 5V.

          I re flowed the charge IC U7000 and it solved the issue! It appears that the PPBUS_G3H 12.6V was disappearing not because of a short downstream but rather it was simply unable to maintain the voltage under load. This is why when I would remove the fuses the voltage would come back and disappear when I would put back the fuses.

          Thanks for the help!

            Comment

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