XPS 13 9370 CMOS battery voltage always low

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  • questore
    Badcaps Veteran
    • Dec 2015
    • 542
    • csongrád
    #1

    XPS 13 9370 CMOS battery voltage always low

    Hi Everyone,
    I have brought you a mistery item
    This laptop have come with some strange faults.
    1. CMOS battery was flat 0v
    Symptoms:
    - After using the laptop and shutting down and removing the AC adapter for at least 1 minute, the laptop never turned on until EC reset (either shorting RTC or removing battery and long pressing power button)
    Amp drawing was stuck at 0.005 milliamps.
    - Laptop cannot really be turned off because it autostarts about 5 sec-1 or 2 minute. (lid sw is not the problem)

    After inverstigation RTCD1 diode had a low value (2.5) on pin #1 and measuring the diode turned out to be faulty so I have replaced it. and also CMOS battery to new.
    Now EC won't freeze anymore after removing the AC adapter BUT...
    After some using and turning off and on suddenly the EC resets and shows "CMOS battery failure" 1 white 3 amber LED error. then starts with resetet BIOS.
    So I have started measured CMOS battery and its only 2,6v (new CMOS battery drained as hell)
    removing CMOS battery revealed that even with main Battery connected the RTCVCC is only 2,55V (RTCD1 output is still 3.12V OK)
    After hooking Lab power supply and injecting 3.0V to RTCVCC the board draws 180 milliams !!!! nothing is getting hot and RTCVCC line has a Mohms resistance but something is taking much more power than it should.
    I'm thinking since POWER SW is also connected to this line, maybe this is why the laptop autostarts.
    Do you have any theory why this is happening?
    Tags: None
    • mon2
      Badcaps Legend
      • Dec 2019
      • 14628
      • Canada
      #2
      You can remove the pull-up resistor mated to the power switch and this +RTCVCC rail to investigate if that is a root cause. Each leg of this power rail appears to have a local part that can be temp removed to check if that load is the fault or not.

      Confirm the 2 resistors are ok @ RTCR1 and RTCR2.

      Click image for larger version Name: rtc.png Views: 25 Size: 42.0 KB ID: 3736073

        Comment

        • questore
          Badcaps Veteran
          • Dec 2015
          • 542
          • csongrád
          #3
          Originally posted by mon2
          You can remove the pull-up resistor mated to the power switch and this +RTCVCC rail to investigate if that is a root cause. Each leg of this power rail appears to have a local part that can be temp removed to check if that load is the fault or not.

          Confirm the 2 resistors are ok @ RTCR1 and RTCR2.

          Click image for larger version Name: rtc.png Views: 30 Size: 42.0 KB ID: 3736073
          Both resistors have a good value.

            Comment

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