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    Lenovo Thinkpad P50, no power

    Hello,

    I'm looking for pointers/ideas to find what's wrong with the motherboard of my Lenovo Thinkpad P50.
    Motherboard: BP500, NM-A451, VER 1.0
    Schematics & Boardview: https://www.badcaps.net/forum/showth...hlight=NM-A451

    Here is what I know up to now:

    The computer was never in contact with liquid, nor dropped.
    It suddenly lost power while I was working. It was attached to the docking station, with the battery inside. Not any lights or other sign of life when I try to power on. The LED of the DC-in jack does not light up.
    The charger and the battery do provide adequate voltage.
    I tried to fully reset the BIOS' by removing the CMOS battery and I tried power on with only the battery and only the charger.
    I discovered that the CMOS battery was dead (near 0 V); I bought a new one, but it does not solve the issue.
    I attached a 3V battery and measured a current draw of ~2.5 mA (off state), which seems huge to me considering that at this rate it would be empty in 3 days. Does it provide any hint?

    Visually, I do not see a problem on the board. There are some stains here and there, as illustrated in red in the attached picture, but I suppose it is just flux from manufacturing.

    I started measuring voltages and looking at continuity, thanks to the schematic and boardview. I removed all components except the fans and heat-pipes before measuring. The CMOS battery is not attached either. Should I attach it?
    VINT20 is OK everywhere I measured it. VREGIN20 is OK at R515 and R516.
    VCC3MP and VCC5MP are also OK at the output of the converters (coils).
    I got no voltage for VCC3M(P) at PR64.
    I measured ~3.3 V for VCC3SW at several locations, but I got no voltage at R526, R529, PR256, PR257, PR295. I suppose it's not normal but I'm not sure.

    From here, I'm uncertain how to proceed further in an effective way to find the source of the problem.
    I had a course of electronics at university several years ago, but I'm not an electronics engineer or technician. It's the first time I tinker with a board.

    Thank you for any advice.
    I'll gladly provide any further info. Later, I'll post a picture of the board with what I measured.
    Attached Files

    #2
    Re: Lenovo Thinkpad P50, no power

    Hi. Have not reviewed the schematics for this board but start with the dc adapter that powers this box.

    Vin good and within specs of the adapter markings once attached to the logic board?

    Then continue to review each power rail downstream into the logic board and compare to the schematics.

    What is missing?

    The cmos battery will not impact this operation.

    You may have a bad capacitor which are usually tantalums. These are the small black ones with a white stripe. They die over time and present a short circuit on the power rail. Then that power rail shuts off or gets killed due to excessive current draw.

    Comment


      #3
      Re: Lenovo Thinkpad P50, no power

      Measure resistance to ground on RTCVCC.
      OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

      Comment


        #4
        Re: Lenovo Thinkpad P50, no power

        Thank you both for your help!
        Originally posted by mon2 View Post
        Vin good and within specs of the adapter markings once attached to the logic board?
        Yes, as said above, there is ~20 V at VINT20.

        Originally posted by piernov View Post
        Measure resistance to ground on RTCVCC.
        Aah, those are small components... I attached pictures of them.
        I measure 3-5 ohm (R108_1, R109_1, C71_1 etc.). On R31_1 I get a bit more but I think it's due to a bad contact with my probes, which are rather big.
        I measure 20.4 kohm on the other side of those resistances, which correspond to their value (to ground).
        Should I therefore assume that one of the 3 tiny capacitors (C71, C63, C288) or the Skylake PCH is dead?

        By the way, at D1_1 I measured 200 ohm to ground with SW1 up and 0.915 Mohm with SW1 down. The last value is basically R31. At D1_2: 40.3 kohm with SW1 up and 120.4 kohm with SW1 down.

        Thanks a lot!
        Attached Files

        Comment


          #5
          Re: Lenovo Thinkpad P50, no power

          Originally posted by ThMC View Post
          Aah, those are small components... I attached pictures of them.
          I measure 3-5 ohm (R108_1, R109_1, C71_1 etc.). On R31_1 I get a bit more but I think it's due to a bad contact with my probes, which are rather big.
          I measure 20.4 kohm on the other side of those resistances, which correspond to their value (to ground).
          Should I therefore assume that one of the 3 tiny capacitors (C71, C63, C288) or the Skylake PCH is dead?
          Yes, you can remove the capacitors (just shift them away from one pad) and see if the resistance to ground increases. If no the PCH is most likely dead.
          OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

          Comment


            #6
            Re: Lenovo Thinkpad P50, no power

            Thanks. I'll try to shift them away from one pad. Given their size it will be tough.

            Comment


              #7
              Re: Lenovo Thinkpad P50, no power

              Hello,
              My reply after quite some time...

              So, I tested what you suggested and the capacitors are all OK, so the Intel PCH chip is likely dead.
              Such a pity for a laptop which was barely more than 4 years old.

              Difficult to find repair services in or near my country, which replace such a chip, and it looks too expensive. In the meantime, I therefore bought a new laptop.
              However, I believe the rest of the P50 is still valuable and maybe the motherboard could be used for parts.

              What is better? Trying to sell it "as is" telling the MB is dead? Or sell individual components (RAM, etc.)?
              Do you have suggestions?


              Thanks again for the help. I learned a lot about MB in this adventure.

              Comment

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