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Dell E7250 5V and 3V missing

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    #1

    Dell E7250 5V and 3V missing

    I got a dell E7250. That was dead and when plugged in the charger light would go off.
    I found out that PL700 was short. I removed it.
    Then next I saw that some capacitor was short. Found that PC715 was short. Remove that and now there are no shorts in 19v rail.
    Next I wanted to see if 5V_ALW and 3V_ALW were present and no there is no 3V or 5V present.

    Could somebody help. I cannot understand from the schematic what chip does create 5V_ALW and 3.3V_ALW?
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    #2
    Start with the main power adapter feed. Is the power adapter the original? Then check the voltage on the 2*dcin mosfets. Post each measurement.

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      #3
      Power adapter: 1 original 1 aftermarket. Confirmed working on different dell.

      PQ4 in:19,4V out:19,4V
      PQ700 in:19,4V out:18,9V

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        #4
        PU100 is the creator of these always on (ALW) power rail. The EN (enable) lines are from the EC which shows it is powered by the RTC battery. Confirm the battery is ok for the real time clock.

        Confirm the voltage to ground of pin # 3 and also pin # 13 on PU100. Each is a LDO that should output the respective rails.

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          #5
          I misdiagnosed the short a bit.
          The PL700 that I removed is needed in the circuit. The shorted capacitor confused me.
          I soldered PL700 back. Now the board is trying to start and leds flash when power is inserted. When I push power button the board is trying to start but then reseting. I think it might be charging/battery issue.

          The battery charge icon is flashing (like charging) even when there is no battery connected. I connected battery and it started charging battery. (confirmed with multimeter).
          I'll let the board to charge the battery and then try to start with battery.

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            #6
            I now tested the board a bit.

            I push the power button.
            Lights come on, power light is on.
            Screen backlight flashes for a millisecond and then all lights go off (board resets).

            This is exactly the same with AC adapter and battery. Even disconnected screen and it is still same.

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              #7
              I used some randon DDR3, but the laptop needs DDR3L. I grabbed a DDR3L and it is working fine. So it was a shorted capacitor. Thanks!

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