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Lenovo NM-B421 carnage

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    Lenovo NM-B421 carnage

    Lenovo E480 with NM-B421 motherboard came in dead. Pulls about 300ma @ 20V via USB-C and no reaction to power button.

    PU702 (NB691GG-Z) for +1VALWP was clearly shorted, along with PU801 (RT8068AZQW) for +1.8VALW having a hole in it. Along with that, LDO output of PU201 (SYX198BQNC) for +3.3ALW has 7 ohms to ground. Thermal camera shows PU201 getting hot, and the EC (IT8996E-256) is cause of that. +5VALW output is ok.

    These are the faults seen so far. Resistance after PU702 removal (pin 1 was welded to the PCB BTW) is 80 ohms to ground for the +1VALWP rail. As this is connected to the PCH, don't want to waste the effort on ordering in these IC's etc only to find the PCH dead.

    If anyone else has this board working, can you possibly post resistance measurements for the low voltage rails please?
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    #2
    Re: Lenovo NM-B421 carnage

    Apparently the unit was dropped - can't see how that marries up with the damage seen. Anyway, ended up writing it off as likely to have CPU/PCH issues.

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      #3
      Re: Lenovo NM-B421 carnage

      Yes agree with your views. +1V along with +3V LDO shorted =dead PCH in 99% of the cases.

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