Lenovo L40 - only pulsing ACIN

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  • ktmmotocross
    Boardkiller
    • Feb 2014
    • 3559
    • slovakia
    #1

    Lenovo L40 - only pulsing ACIN

    Hello.
    Have this Lenovo L40 that have pulsating VIN. I found that on Charger ic i have only little bit pulse to 3.5V on 88731_ACIN. But when i poking around and measure ohm/not diode mode/ and put blackprobe to ground and red to side of PR100 all start to work and 88731_ACIN goes steady to 4V. after power reset it is same again. Wonder why it can act like this?
    Attached Files
    Last edited by ktmmotocross; 03-13-2020, 05:03 AM.
    Tags: None
    • mcplslg123
      Badcaps Legend
      • Jun 2015
      • 7262
      • india
      #2
      Re: Lenovo L40 - only pulsing ACIN

      Got a somewhat similar case last week. It was sony mbx270 with pulsating +19V rail(Laptop boots from a charged battery). The voltage divider circuit has 4 resistors 45K,45K,69K,435K. took all of them out and measured to findout all re ok. Soldered them back and it worked but after 30 mIns -same story of pulsing B+. Ultimately replaced all the 4 resistors and its working fine for last 5-6 days. Dont know why....

      (Charging Ic was installed new, so it was not charging ic)
      Last edited by mcplslg123; 03-13-2020, 10:30 PM.

        Comment

        • mcplslg123
          Badcaps Legend
          • Jun 2015
          • 7262
          • india
          #3
          Re: Lenovo L40 - only pulsing ACIN

          Here is the pic
          Attached Files

            Comment

            • ktmmotocross
              Boardkiller
              • Feb 2014
              • 3559
              • slovakia
              #4
              Re: Lenovo L40 - only pulsing ACIN

              i quit from make proper repair. it have broken display so i wont bother with it. i removed pq12 to have stable 88731_ACIN. battery is charging, works without/with power so no other repair needed.

                Comment

                • Spider1211
                  Badcaps Veteran
                  • Oct 2019
                  • 532
                  • Mauritius
                  #5
                  Re: Lenovo L40 - only pulsing ACIN

                  I had a similar issue recently on an Asus, my issue was a shorted MOSFET on the battery charger side.

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