Dead t480s, trying to troubleshoot. May have found something.

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  • dropfry
    Member
    • May 2009
    • 19
    #1

    Dead t480s, trying to troubleshoot. May have found something.

    Hello. I have a lenovo that will not show any indication of life. No led, sound or anything really. So I took the motherboard out and started testing points according to the advice in this thread: https://www.badcaps.net/forum/showthread.php?t=102409


    PU201 is Showing 6v

    VREG3/5 show a high value (around 20v) for a split second then drop down very quickly. Hold around 1v but then continue to drop to zero. One is showing .2v.

    Fuse PF1 is showing very low voltage (which according to the thread deals with docking and is expected)

    Fuse PF2 shows 20v.

    I don't have a bench power supply and good way of checking thermals so I did something I've seen on indian repair channels on youtube. I put my individual finger tips spread out over several different ICs until I found one that burned me.

    It was a chip that reads "Lenovo bd4179 826 h69"

    Googling that I found one from china for $5. I'm not sure if this is the offending component. It didn't actually burn me, but it is uncomfortably hot and I wouldn't want to leave my finger on it. If I did have a thermal cam it would no doubt light up.

    What do you guys think? Are there other test points I should check to zone in on this and verify it before ordering the chip from China? If this chip is what failed did it probably wipe out other components as well that I need to order or is the damage typically sustained to just this ic?
    Tags: None
    • Techtiger
      Badcaps Legend
      • Oct 2014
      • 1601
      • france
      #2
      Re: Dead t480s, trying to troubleshoot. May have found something.

      The measurement PU201 is not correct 6V, and the correct voltage for VREG3 should be 3.3V, while VREG5 should be 5V. If the voltage is set to around 20V, MOB will stop working. The TPS51285B produces 3V and 5V always-on and low-dropout (LDO) regulators for the motherboard. Is it a Mosfet what is the Component on schematic PQXXX ?bd4179 826 h69
      Last edited by Techtiger; 09-29-2023, 08:27 AM.

        Comment

        • dropfry
          Member
          • May 2009
          • 19
          #3
          Re: Dead t480s, trying to troubleshoot. May have found something.

          Originally posted by Techtiger
          The measurement PU201 is not correct 6V, and the correct voltage for VREG3 should be 3.3V, while VREG5 should be 5V. If the voltage is set to around 20V, MOB will stop working. The TPS51285B produces 3V and 5V always-on and low-dropout (LDO) regulators for the motherboard. Is it a Mosfet what is the Component on schematic PQXXX ?bd4179 826 h69
          The schematic I have says:

          KL1KR-1
          VER 4.02
          Nov/1/2017

          MOD Edit ,link to schematic https://www.badcaps.net/forum/showthread.php?t=81061

          Reminder: rules and organization of this sectionhttps://www.badcaps.net/forum/showthread.php?t=117483

          I'm not positive but the best lettering near the IC says: U101. I took a couple screenshots and added a green box to where the IC is sitting.
          Attached Files
          Last edited by SMDFlea; 09-30-2023, 07:20 AM.

            Comment

            • Techtiger
              Badcaps Legend
              • Oct 2014
              • 1601
              • france
              #4
              Re: Dead t480s, trying to troubleshoot. May have found something.

              Originally posted by dropfry
              The schematic I have says:

              KL1KR-1
              VER 4.02
              Nov/1/2017

              This one: **********************
              I'm not positive but the best lettering near the IC says: U101. I took a couple screenshots and added a green box to where the IC is sitting.
              If you have soldering skills, you may be able to replace the component that is causing the overheating. It's possible that some other component is shorting to ground, which is why it's getting hot.
              Last edited by SMDFlea; 09-30-2023, 07:17 AM.

                Comment

                • dropfry
                  Member
                  • May 2009
                  • 19
                  #5
                  Re: Dead t480s, trying to troubleshoot. May have found something.

                  I took a thermal image of it plugged in and the suspected chip lit up. So did a couple, I'm guessing resisters? As well as a third, small black square. I added pictures.

                  On the schematic their code is Rg34 and R633. Not sure about the third little black box.

                  I guess I should remove this chip, plug the board back in and if those components don't get hot then I can replace the chip and it won't blow out? I have it's replcement but only ordered one.
                  Attached Files

                    Comment

                    • Techtiger
                      Badcaps Legend
                      • Oct 2014
                      • 1601
                      • france
                      #6
                      Re: Dead t480s, trying to troubleshoot. May have found something.

                      Pin 45 (VIN) of U101 is connected to the +20V line (TBT_VBUS20_F) through 2 Diodes (D83/D84), 2 resistors (R633/R644), and capacitor C603. You can test these components one by one using a multimeter in resistance mode. In most cases, capacitors tend to be the most common component to fail

                        Comment

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