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MacBook Pro 820-2850-A logic board doesn't boot

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    MacBook Pro 820-2850-A logic board doesn't boot

    Hi,

    I'm new to the forum and would appreciate some help. Hopefully I posted this correctly. I purchased a non-working 2010 15” Mac Book Pro i7-2.66 4GB RAM with a 820-2850-A logic board with the intent of repairing and reselling it. The computer case is in excellent shape with no signs of water damage or corrosion but it does have a cracked LCD screen. This is my first attempt to trying to trouble shoot one of these boards. I read through Rossman's presentation (very useful) and watch many related videos. I have been working on this for days and need some help.

    Symptom: Green light on charger, fans spin at low speed, power light comes on front edge. No chime, no display, no USB mouse LED. After a minute, the fans shut down and the system starts again. Does this with or without a battery. Appears system is not making it out of POST.

    Found PPVCORE_S0_CPU decoupling cap C1627 was completely missing and decoupling cap C1632 was half off. Perhaps someone accidentally scraped them off when removing the bottom cover. Reattaching the half off cap and replacing the missing cap had no affect but may still be related as will become apparent below.

    Powering card on bench results in the following: Green charging light comes on, the fans stay off for 7 seconds, then spin fast for about 1 second and then slow for 15 seconds then fast for 30 seconds. The cycle then repeats. Again, no chime and no USB mouse LED.

    All power rails appear to be present and system is entering S0 state.

    The only anomaly so far is that PPVCORE_S0_CPU (the same power rail that had the missing caps above) is pulsing about 1/sec, i.e. it is normally 1.08V but pulses down to about 0.8V about 1/sec. The schematic indicates it should be at 1.25V but I got the same 1.08V reading (without pulsing) on another good system. Both phases seem to be working identically.

    Pulsing can be traced back to the Gates on Q7410, Q7415, Q7420 and Q7425 and corresponding output pins on U7400 as well as the CPUIMVP_ISEN1N, 1P, 2N and 2P lines.

    U7400 V5FILT (pin38) and V5IN (pin26) are 5V and do NOT pulse.

    PPBUS_CPU_IMVP_ISNS does NOT pulse and is steady at 10 volts.

    U7400 pin 13 PSI input (CPU_PSI_L) from the CPU is pulsing low (0.8V to 0V) at same rate.

    PPVCORE_S0_CPU_VCAP0, PPVCORE_S0_CPU_VCAP1 that are sourced by the CPU are also pulsing at 1Hz but PPVCORE_S0_CPU_VCAP2 is not. Can't explain this.

    Also, U7400 VID0 - VID 6 (pins 20 - 14 respectively) are also apparently being driven by the CPU but some are also pulsing as follows:

    VID 0: normally 0.8 pulses down to 0.0
    VID 1: normally 0 pulses up to 0.8
    VID 2: normally 0 pulses up to 0.8
    VID 3: steady 0
    VID 4: normally 0 pulses up to 0.8
    VID 5: steady 0.8
    VID 6: steady 0.0

    I measured all the resistors in the PPVCORE_S0_CPU sensing circuits on page 68 and they match from Phase 1 to Phase 2 and to values on a junk board.

    I don't think the CPU is completely dead since CPU_PSI_L and the CPUIMVP_VID0-VID6 signals that come from the CPU are active. If so, it looks like something is wrong with the U7400 PPVCORE_S0_CPU circuitry. I suspect PPVCORE_S0_CPU sensing is triggering every second and then the system shuts down after a minute but I can't figure out what is causing this.

    Any suggestions on how to proceed would be greatly appreciated.

    Thanks!!!

    #2
    Re: MacBook Pro 820-2850-A logic board doesn't boot

    Any history? (liquid damage…)
    Replaced C9560 already?
    Known good RAM? Beeping without RAM? Same CPU VCore behaviour without RAM?
    Tried another BIOS?


    CPU sets its own VCore voltage, it usually starts around 1.1V and may drop below 1V, like 0.9V when power management kicks in (typically during/after POST, RAM must be recognized).
    OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

    Comment


      #3
      Re: MacBook Pro 820-2850-A logic board doesn't boot

      Thanks piernov for getting back to me.

      Any history? (liquid damage…). Was advertised with this issue prior to purchase. Other than that don't have any history. No evidence of liquid damage or corrosion. Very clean unit except for a minor amount of dust.

      Replaced C9560 already? Yes with 3 terminal capacitor from Rossmann Group. Also changed thermal grease. No change in behavior.

      Known good RAM? Works same with known good RAM.

      Beeping without RAM? Yes, single beep (and sleep indicator flash) when connected to chassis, no if not.

      Same CPU VCore behaviour without RAM? Without RAM, PPVCORE_S0_CPU is steady 1.1V. Pulsing also occurs with 1 RAM module in either slot.

      Tried another BIOS? No. Could you suggest a link on how to do that?


      CPU sets its own VCore voltage, it usually starts around 1.1V and may drop below 1V, like 0.9V when power management kicks in (typically during/after POST, RAM must be recognized). Does this mean we can at least rule out a dead CPU?

      Again thanks so much for your help!!!

      Comment


        #4
        Re: MacBook Pro 820-2850-A logic board doesn't boot

        Forgot to mention that without RAM, fan speed remains constant at slow speed.

        Comment


          #5
          Re: MacBook Pro 820-2850-A logic board doesn't boot

          Hi,

          Did some more investigation and it appears that the CPU IMVP VCORE Regulator circuit may not be working correctly.

          Observed CPUIMVP_UGATE 1 and 2 were ringing badly and could not establish a stable trigger on the scope.

          CPUIMVP_LGATE 1 and 2 seemed fine.

          Diode mode voltage readings on Q7410 and Q7420 Gate inputs were way off from a donor board at 0.023 vs 0.571V respectively (read 0.464V on a working system). Also their Source Pins were 0.020 vs 0.105V respectively.

          PPVCORE_S0_CPU pulses between 1.1V and 0.88V at about 1HZ with many small pulses riding on top of the DC. After a minute the system shutdown and automatically restarts.

          Considering PPVCORE_S0_CPU decoupling cap C1627 was completely missing and decoupling cap C1632 was half off when I received this unit, perhaps FETs Q7410 and Q7420 and/or U7400 were damaged when that trauma occurred.

          Regarding lower FETs Q741 and Q7425 - Since the Lower gates seem to be working and their Gate and Source diode mode readings match a donor board and working board at 0.360V, I am wondering if I can leave them alone.

          Another question is the schematic says U7400 is a TPS51621 but the part is stamped with TPS51983 on the bad board, donor board and working board. I assume I should order replacement parts based on what is stamped on the part, not what is shown on the schematic but would appreciate confirmation that is correct. I could pull the parts from the donor board but thought it might be safer to get brand new parts.

          From watching Louis Rossmann, he recommends changing the Power Control IC at the same time the FETs are changed. However, given the above, is there a chance that I can get by with replacing just U7400 or just the 2 FETs?

          Again, I am new to troubleshooting these boards and would appreciate any guidance that can be provided.

          Thanks.

          Comment


            #6
            Re: MacBook Pro 820-2850-A logic board doesn't boot

            A good detailed post, so apologies if I've missed it -

            I think these need a battery but could be wrong!
            3v on u7400 pin 31?
            anything on pin 35 CPUIMVP_VR_ON or is that pulsing?
            whats the clock area looking like? all voltages and signals present on clock chip?

            Comment


              #7
              Re: MacBook Pro 820-2850-A logic board doesn't boot

              Thanks lucky dip for getting back to me. Greatly appreciated!

              Regarding the need for a battery - these readings are without a battery connected, just the logic board on the bench.

              As described above, system does not boot (no chime) when fully connected with a known good battery.

              Fan behavior is different with and without battery and with and without RAM.

              Signal pulsing behavior is different with and without RAM.

              Below are the requested readings:

              3v on u7400 pin 31? Yes, stable 3.3V
              anything on pin 35 CPUIMVP_VR_ON or is that pulsing? Stable 3.3V, no pulsing.
              whats the clock area looking like? all voltages and signals present on clock chip? Assuming you mean U2700, clock outputs appear to be present.

              Thanks again!

              Comment


                #8
                Re: MacBook Pro 820-2850-A logic board doesn't boot

                These 2850's can be a nightmare! can you check ALL_SYS_PWRGD? Did you get a chance to try another bios?

                Comment


                  #9
                  Re: MacBook Pro 820-2850-A logic board doesn't boot

                  lucky dip, sorry didn't get back sooner, been under the weather all week. Thanks for your suggestions.

                  ALL_SYS_PWRGD is steady 3.3V, no pulsing.

                  Did not try bios yet. Think I will try replacing U7400 and upper FETS Q7410 and Q7420 with parts from a donor board and see if that cures the pulsing. Will leave lower FETS Q7415 and Q7425 alone for now since they appear okay.

                  Will post results.

                  Any further suggestions welcome.

                  Comment


                    #10
                    Re: MacBook Pro 820-2850-A logic board doesn't boot

                    Sorry for delay in this update.

                    I replaced U7400 and then verified Q7410, Q7415, Q7420 and Q7425 diode mode voltages appeared okay, specifically that Q7410 and Q7420 still appeared bad and Q7415 and Q7425 still appeared okay compared to a donor board and a known good board.

                    Then proceeded to remove Q7410 and Q7420 from both the donor board and the board i'm trying to fix.

                    Then reinstalled the donor Q7410 and Q7420 on the board being fixed.

                    Diode mode voltage on Q7410 now appears okay but Q7420 does not. Pin 4 reads 1.3 volts on board being fixed compared to about 0.6 volts on known good board. Same reading at both ends of the trace at U7400 as well as Q7420. To avoid potentially more damage, I did not power on the board.

                    Perhaps heat from hot air gun on FET side of board damaged the FET or U7400 on the reverse side of the board?

                    Since I'm not sure which part is suspect, I will order both U7400 TPS51621QFN and Q7420 RJK0365DPA-02 and try again starting with Q7420.

                    Any suggestions or comments are welcome. Will post result.

                    Comment


                      #11
                      Re: MacBook Pro 820-2850-A logic board doesn't boot

                      Maybe he is stuck in efi, try to replace from donor the efi ic. Got one air that had the same behavior. Fan spins, trying trying to boot. No image no chime- restarted. Replaced efi ic and it worked.

                      Also check traces ...

                      Comment


                        #12
                        Re: MacBook Pro 820-2850-A logic board doesn't boot

                        Thanks crazeej, will try your suggestion and post result.

                        Comment

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