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820-2915, USB supply (U4600) burned -> replaced now short on PP5V_S0, U9500 HOT!

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  • 820-2915, USB supply (U4600) burned -> replaced now short on PP5V_S0, U9500 HOT!

    Hi guys,

    this one had an exploded u4600 when it arrived (it smoked while the customer was testing it) and I replaced it with new one and the short seems to be gone.

    now when I turn it on the fans start and stop after 1-2 secs OR can last upto 10sec - this is when I noticed that U9500 gets REALLY hot and by measuring around I got a diode mode reading on 0,018 on PP5V_S0. Of course I have no PP1V5_GPU_REG and I measure 0V on PPVCORE_S0_AXG, too.

    I see PP5V_S0 is generated by Q7860, should I remove that and inject 5V with a power supply to see what gets hot? (there is also C7860 there which I may also have to remove just incase it shorts).

    Should I replace U9500 first? Since it gets hot maybe thats the one shorted to ground?

    Where would you start?

    Please advise


  • #2
    Surge on 5V bus, there may be lots of damage. Start with U9500 and go from there. Usually U4800 is the first one to die, check 5V_S3 for low resistance too.


    • #3
      ok duke I will replace U9500 today and let you know..

      diode mode to ground for PP5V_S3 is 0,381 when it was close to zero before u4600 replacement. Resistance between GND and PP5V_S3 is approx. 16.3Kohm.

      u4800 is important for what? I see "IR Support" as title in the schematic.. or you mean it could also short?



      • #4
        update: I removed U9500 which was getting very hot but measuring PP5V_S0 at C9501 gives 0.023 diode mode. This means the short is present elsewhere on this rail but was also somehow affecting U9500.

        should I inject 5V now? You see me reluctant because I would really like to follow the correct procedure with this one without "sudden moves" ...


        • #5
          Yeah inject 5V and see what heats up, but this board will have extensive damage. Probably 50% of chips on 5V_S0 bus are dead, starting with all the ISL chips.


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