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    820-00840 no post

    Hi all,

    I'v got a macbook pro 13 inches with motherboard 820-00840 wich came to me because it gave no image to external display after U3200 replacement. While testing it off the case it over heated around U3100, only realized when grabbing the board and now it doesn't chime most of the times, but when it does it gives image to internal and external display but with some dot's on the screen.

    Always turns on with 20V.

    I can't think of anything besides maybe a CPU failling on me because of the heating with no fan, but I would like your opinion on this.

    Sorry for my English since it is not main native language.

    #2
    Re: 820-00840 no post

    Hi. Received the same model late yesterday for service. Client reported high heating of the unit and it would not turn on.

    1) what are the specs of the power adapter (type C) that you are using ? We used 45W from CUI that worked after leaving the unit plugged in for a while. Then the battery low graphic appeared. It has been charging since last night so will see upon reaching the office.

    2) Agree that there are some hot spots on the logic board. Not yet sure what is the root cause of this fault. With the dead battery on this unit, the power was cycling for us and eventually calmed down to a steady current draw @ 20v.

    What is your current draw ? Are you using the Apple original or different Type C power adapter ?

    Comment


      #3
      Re: 820-00840 no post

      I use a USB C charger 90W, but it is not original.

      When the current gets stable is around 0.55A, with no chime nor image but I have CPU and GPU voltage. When it chimes the current jump to 0.77A, probably because of the display and backlight, but image stays black with some dots. Almost like a graphics anomaly.
      If the battery is connected sometimes it shows the battery empty image and I can see the no system folder flashing with artefacts.

      Comment


        #4
        Re: 820-00840 no post

        Hi.

        1) Do you have USB ammeter ? Do you see 20v being negotiated everytime after first boot ? This will confirm your ACE controllers (USB power delivery controllers from TI) are operational.

        2) This logic board = flexgate issues. You may be facing this fault with your unit. Perhaps with some strong arm chats with Apple, they will replace the display assembly and perhaps also the butterfly keyboard. Look into this first. We have done this a few times on behalf of local owners of this box with success.

        3) U3100 = ACE controller (power delivery) - has it been replaced yet or is the original and with a flaky operation ?

        Most state the controllers should be replaced in pairs and must be sourced from reliable vendors on Aliexpress.

        If it is getting unusually hot then the part is likely to be defective but not having an original adapter could put the blame on the power source.

        That is, power delivery is built on contracts (voltage & current as a pair = contract). When the adapter mates with the logic board, the logic board (via ACE controller) pings the Type C adapter to extract out the database of contracts.

        From the contract database, the logic board will select the best choice to power the board. This should be 20V @ xx amps.

        Do you know if you truly have 20V as the input to the logic board ? Or maybe you have > 20V as the input which can cause heating faults inside the ACE controller.

        At the very least, consider a branded power adapter that is Type C. We picked up the LVSUN (96W Type C) when we were in HK for $20 USD (cash at the trade fair) - one of the best investments we have made. Only died recently due to a low life scamming us on Ebay with stolen parts and BGA devices having solder blobs. Ebay refunded our money in full but this thief killed our power adapter. I think if it was the Apple original adapter, we would have survived this event.

        Do consider an alternate power adapter for at least testing. You can try Amazon and return it if you really do not need it.

        4) Otherwise, when you do NOT hear the chime, what is the voltage of PPBUS_G3H ?

        Comment


          #5
          Re: 820-00840 no post

          Hi mon2 and thanks for taking the time to help me, I'll try and reply to all your questions.

          Yes I do have a USB ampmeter, and yes the 20V are always being negotiated.
          The current draw gets different values when not chiming, 20.8V with 0.52A, or 0.45A or 0.61A.
          The time it chimes it goes on last step from 0.48 to 0.73A, probably because of the backlight.

          About the charger I've testes with a original one with the same results.
          Made some measures around the board.

          PPDCin_G3H - 19.48V
          PPBUS_G3H - 13.04V
          PP5V_S5/S4/S0 - 5.12V
          PP3V3_S5/S4/S0 - 3.32V
          PP3V3_G3H - 3.40V
          PP1V_S5G - 1.003V
          PP1V_S3/S0G - 0.994V
          PP1V35_DDR_CLK - 1.337V
          PP1V8_S5G/S3/S0 - 1.794V

          L7030 - 13.06V
          L7730 - 1.052V
          L7430 - 0.679V
          L7410 - 0.680V
          L7420 - 0.679V
          L7210 - 0.839V
          L7220 - 0.839V
          L7370 - 0.772V
          L8060 - 1.003V
          L7900 - 1.001V
          L8030 - 1.202V
          L7960 - 0.956V

          after chime PPDCIN_G3H measures 19.06V. PPBUS_G3H stays the same.

          Comment


            #6
            Re: 820-00840 no post

            What are the voltage values when the board does not chime?

            Have you performed a PRAM reset?

            Comment


              #7
              Re: 820-00840 no post

              The voltages mentioned are with no chime and all stay the same after chime except for PPDCIN_G3H which has 19.48V no chime and 19.06V with chime.

              However noticed that:

              L7210 has 0.839V with no chime, 0.830V with chime
              L7220 - 0.839V no chime, 0.824V with chime
              L7370 - 0.772 no chime, 0.812 with chime.

              I don't know if such small values mean anything.

              Forgot to mention, about the flexgate I'm currently working with a different display and the screen anomaly also present with external display.

              there are a few lines that I couldn't measure for comparing the value with no chime vs chime, they are:

              PP1V_S3
              PP1V_S0G
              PP1V35_DDR_CLK.

              Yes done PRAM and it get's 0V at the PPVCCGT lines. only way after that is to do a SMC reset.

              Already replaced the smc with a donor board but the machine stop working after that, can't tell if the donor smc was good.

              Comment


                #8
                Re: 820-00840 no post

                L7370 = PPVCCSA_S0G_R and this voltage appears to be too low to operate correctly.

                See here:
                https://boards.rossmanngroup.com/thr...7370-hs.55830/

                So WITH CHIME, you are probably borderline ok but still on the low side of this required voltage rail.

                WITHOUT CHIME, you are below the required voltage.

                Comment


                  #9
                  Re: 820-00840 no post

                  ok, made some new measurements especificaly on L7370 and realized that before I have PPVCCGT lines, L7370 presents 1.045V, after I have PPVCCGT lines it stays within the values mentioned before. I'll look around this and post feedback

                  Comment


                    #10
                    Re: 820-00840 no post

                    ok a client brought one exacly the same model, and I've done some analisys and the voltage on L7370 it's exacly the same, so I don't think that there is a problem there.

                    Do you think that the U2800 could cause this problem?
                    I ask because I saw a post while searching (can't remember where) of someone that replaced some capacitors and resistor close to it, and after that it presents a similar anomaly.

                    Comment


                      #11
                      Re: 820-00840 no post

                      Never solved the problem, client came and pick it up. Thanks for the help

                      Comment

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