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    820-2850A wont turn on

    I have a 2010 macbook pro 820-2850A that won't turn on. no light on charger.

    PPBUS_G3H is 0.4v
    pp3v42_g3h is 3.4v


    U6900:
    SYS_ONEWIRE 2.8V
    ADAPTER_ONEWIRE 2.8
    ADAPTER_SENSE 2.8
    SMC_BC_ACOK_VCC 3.4V

    U7000:

    CHGR_DCIN is 18.4v
    CHGR_ACIN is 0.4v <-----

    SO CHGR_ACIN And PPBUS_G3H is not correct.

    not sure were to go from here.
    Attached Files

    #2
    Re: 820-2850A wont turn on

    Bad R7010, bad C7011 or bad U7000. Could be bad traces/pads/probe points if it's liquid damaged.

    EDIT: and the onewire circuit is supposed to be a bit closer to 3.42V.
    Could be bad R6929, bad U6900, bad SMC or pulled down on DC-in board/Magsafe itself. Liquid damage can be another factor as well here.

    PS: this will probably need a C9560 replacement at the end.
    Last edited by piernov; 07-19-2019, 03:36 PM.
    OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

    Comment


      #3
      Re: 820-2850A wont turn on

      I replaced R7010, C7011, U7000, R6929, and U6900 from a Donor board. no changes in voltages. I am hoping it's not the SMC as I don't have one and don't know were to find one.

      Comment


        #4
        Re: 820-2850A wont turn on

        Do one thing at a time, no need to add more possible issues than there are already. Also no need to replace randomly components before at least checking if they could be the issue. You haven't confirmed/denied liquid damage either.
        Either chose to pay attention to why SYS_ONEWIRE is lower than expected or why CHRG_ACIN is at 0V. Those seem to be separate issues.

        Taking the CHRG_ACIN path:
        You can start for example by measuring voltage on both sides of R7010, to make sure DC-in voltage reaches pin one and that pin 2 is indeed at 0 volt.
        When this is confirmed you can measure resistance across R7010 to know if it's bad (higher than expected), then check for resistance to ground on pin 2, which is supposed to be higher than 9kohms.
        If it's lower something is shorting it to ground, either C7011 or U7000. If it's correct, then there is a break in a line somewhere, or U7000 can still be pulling it down. Use continuity mode between components to check if there's a break in the line, but usually inspecting under microscope gives it right away.

        Then paying attention to SYS_ONEWIRE:
        You can check votage&resistance on R6929 as above, then you can remove U6900 to isolate SYS_ONEWIRE and see if the voltage goes up.


        There are troubleshooting steps and a thought process associated with each repair. I can't walk you through everything, it's not rewarding and every answer I give takes a lot of time and resources to elaborate. I prefer giving hints and having people find the issue themselves. Which should be more efficient and have a higher success rate, because the board is not in front of me. I'd recommend watching some Louis Rossmann videos. There are a lot of videos related to the above issues.
        OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

        Comment


          #5
          Re: 820-2850A wont turn on

          Piernov I do appreciate the help! This is a learning process for me I have watched some of Louis Rossman's videos. That's what got me started in this hobby.

          I measured both sides of R7010 1 is 18.8v 2 is 0.44v and 29.65Kohms.
          R7010 is 09.29Kohms and 09.30 to ground. I will check the rest tomorrow.
          Thanks

          Comment


            #6
            Re: 820-2850A wont turn on

            I have pulled U6900 and and the voltage does indeed go up 3.4v. I still need to check R5075.

            Comment


              #7
              Re: 820-2850A wont turn on

              CHGR_ACIN: that's a bit weird because the resistance of the voltage divider is ok, there's no short to ground, and you replaced U7000 already. The voltage is still too low though. The resistor divider should give a voltage of around 4.4V, but you measure 0.44V. Make sure it's not a a range error on the multimeter or a wrong measurement. Otherwise check the voltage after desoldering U7000.

              SYS_ONEWIRE: if it's 3.4V now that's good. At least the problem here should not be the SMC. You replaced U6900 already so it should be ok. The issue probably comes from the DC-in board or the Magsafe itself.
              OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

              Comment


                #8
                Re: 820-2850A wont turn on

                tried another magsafe 16v only other one I Have. sys_onewire is now 3.4 with u6900 installed! but R7010 1 is 16.5v 2 is still 0.4v my multimeter is auto ranging but never had issues with it. should I pull U7000 and see if R7010 comes up?

                Thanks

                Comment


                  #9
                  Re: 820-2850A wont turn on

                  Ok so SYS_ONEWIRE looks better at least. Note that this will require an 85W Magsafe to turn on, but for now to restore PPBUS_G3H this is good enough.

                  For CHGR_ACIN... yes, I guess the only thing to do is to remove U7000 and see if you finally get 4V.
                  OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

                  Comment


                    #10
                    Re: 820-2850A wont turn on

                    pulled U7000 still getting 0.4v at R7010. checked for continuity between pin 3 of U7000 R7010, R7011 and it's ok. confusing...

                    Comment


                      #11
                      Re: 820-2850A wont turn on

                      What voltage do you get when measuring across R7010? (one probe on one side, the other probe on the other side)
                      OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

                      Comment


                        #12
                        Re: 820-2850A wont turn on

                        I am getting 12.88 at R7010 and started thinking 16v-12.8=3.2v was I reading the multimeter wrong. Here is 2 images, one is the 3.4v on U9000 sys_onewire.
                        the other is R7010 (2) 0.4v Have I been reading this wrong? if so I do apologize for wasting your time!

                        Edit: I don't know why the 18v magsafe is only getting 2.8V to SYS_ONEWIRE but the 16v charger is. should the 18v magsafe be considered bad?
                        Attached Files
                        Last edited by TimT; 07-21-2019, 08:32 AM.

                        Comment


                          #13
                          Re: 820-2850A wont turn on

                          I read 3.98V and 3.412V on the multimeter. If the first measurement at 3.98V is on CHGR_ACIN then everything is fine there.

                          Measure exact voltage again on PPBUS_G3H. If it is still low (less than 12V) measure its resistance to ground. Check if the fuse is burnt too.
                          OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

                          Comment


                            #14
                            Re: 820-2850A wont turn on

                            The 03.98v was for the CHGR_ACIN 3.412V is for sys_onewire. right now I have 0v on ppbus_g3h.
                            F7040 has 0v. and both sides continuity to ground with 000.4ohms

                            Checking pin 23 of U7000 by using the cap C7025 0v there are a few more items I can check on this circuit tomorrow. I will check the multimeter with my Bench power supply and see how it displays various voltages. But sub 1v may display the first digit as 0

                            Thanks!
                            Last edited by TimT; 07-21-2019, 07:30 PM.

                            Comment


                              #15
                              Re: 820-2850A wont turn on

                              OK so 0.4 ohm on PPBUS_G3H means there is a full short to ground. First thing you can do is remove the fuse F7040 and measure resistance to ground on both pads, to see if the short is toward U7000 or toward system.
                              Then using a lab PSU you can inject 1V on the shorted side, and check if anything gets hot. If nothing gets hot (incl. CPU/GPU/PCH) then you can increase the voltage a little and check again.
                              OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

                              Comment


                                #16
                                Re: 820-2850A wont turn on

                                Q7035 was shorting, after replacing that PPB_G3H came up but only to 1.7v and I noticed a slow drain in voltage in about 20 seconds or so it's 0.9v. re-plug the charger back in 1.7 then drains. I think may have only 0.4v at R7010 I did some testing with the multimeter the results are in the images.
                                Attached Files

                                Comment


                                  #17
                                  Re: 820-2850A wont turn on

                                  possible second short. meter sometime is at 0ohms then not.. used my bench power supply but now wont take any power at F7040. installed a battery and PPbus_G3H is 11.25v No lights/fanspin

                                  Comment


                                    #18
                                    Re: 820-2850A wont turn on

                                    If PPBUS_G3H is 11.25 with a battery, it most likely means PPBUS_G3H itself is not shorted.
                                    However the fuse could have blown and the short be isolated before it, on the controller side.
                                    So make sure fuse is not blown and measure resistance to ground on both sides.

                                    Also, for higher chances of fixing the issue, it's always better to replace the MOSFET Q7035 and the controller U7000 at the same time. (maybe even the other MOSFET Q7030).
                                    OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

                                    Comment


                                      #19
                                      Re: 820-2850A wont turn on

                                      The Fuse is good but Q7035 keeps shorting. when i remove Q7035 no short to ground at F7040. I am going to order the 2 mosfet's and u7000 to be on the safe side. I will let you know the outcome. and thanks for the help!

                                      Comment


                                        #20
                                        Re: 820-2850A wont turn on

                                        RJK0332DPB is proving hard to find. anyone know of a alternative?

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