Macbook Pro A1707 820-00281 Stuck @5V

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  • JasonC89
    Member
    • Apr 2023
    • 17
    • Ireland

    #1

    Macbook Pro A1707 820-00281 Stuck @5V

    So I have an Macbook Pro that came in for no power (I dont do a lot og Macbook repairs). After some testing I found it was only getting 5V with very little current draw, if any.
    I searched around for shorts, and didnt find any. No real signs of liquid damage etc.

    Following a couple of questions from other members here I was able to further test voltages etc. Im now at a point where PP3V3_G3H is showing, but only at 2.23V.
    I have 5v on the Enable pin.
    Also the dual diode D6902 is showing :
    5.19V @ Pin 1
    0v @ Pin 2
    4.15V @ Pin 3

    L6900 is measuring @ 2.23V.

    I thought mayber a problem with the diode D6902, or the regulator, but I removed R6923 to isolate it,and now I get the expected 3.4V out from L6900, and also pin 3 on D6902 is showing 5V also.

    Im not sure where to go from here? ISL problem or problem with one of the CD3215?

    Thanks
  • mon2
    Badcaps Legend
    • Dec 2019
    • 13830
    • Canada

    #2
    Remove all power. Meter in resistance mode (not diode).

    Measure the resistance to ground of PP3V3_G3H.

    Post your measurement. With an output low voltage, there may be a heavier than normal load on this power rail.

    Comment

    • JasonC89
      Member
      • Apr 2023
      • 17
      • Ireland

      #3
      Originally posted by mon2
      Remove all power. Meter in resistance mode (not diode).

      Measure the resistance to ground of PP3V3_G3H.

      Post your measurement. With an output low voltage, there may be a heavier than normal load on this power rail.
      I get about 60k and it rises slowly as I keep the probes on it.

      Comment

      • mon2
        Badcaps Legend
        • Dec 2019
        • 13830
        • Canada

        #4
        This resistance is fine - no short here.

        5.19V @ Pin 1
        0v @ Pin 2
        4.15V @ Pin 3
        That is a large voltage drop on pin # 3. Remove all power. Meter in resistance mode, not diode mode. Measure the resistance to ground of pin # 3 of D6902.​

        Comment

        • JasonC89
          Member
          • Apr 2023
          • 17
          • Ireland

          #5
          Originally posted by mon2
          This resistance is fine - no short here.



          That is a large voltage drop on pin # 3. Remove all power. Meter in resistance mode, not diode mode. Measure the resistance to ground of pin # 3 of D6902.​
          Yes I thought that too, removed D6902 and it still had the same power drop? I then removed R6923 and I got 5V on pin 3 of D6902 (D6902 still removed), I then resoldered D6902 back and the voltage stayed at 5V on the pin 3 output.

          testing the resitance of pin 3 D6902, I again around 300k, which again rise slowly as I keep the probe on it.

          Comment

          • mon2
            Badcaps Legend
            • Dec 2019
            • 13830
            • Canada

            #6
            U6903 sounds to be defective. Confirm the FB resistors @ R6910-R6913. U6903 may need to be replaced. Keep R6923 off the board till this rail is stable and matches the schematic voltage. BTW, yours is the 2nd case in the 2nd day with an identical fault @ U6903.

            Comment

            • JasonC89
              Member
              • Apr 2023
              • 17
              • Ireland

              #7
              me
              Originally posted by mon2
              U6903 sounds to be defective. Confirm the FB resistors @ R6910-R6913. U6903 may need to be replaced. Keep R6923 off the board till this rail is stable and matches the schematic voltage. BTW, yours is the 2nd case in the 2nd day with an identical fault @ U6903.
              Okay, so you think U6903 is defective even though after I remove R6923 off the board, pin 3 on D6902 seems to be normal and also pin 2 of L6900 shows the correct 3.4V, instead of the 2.2V I was getting with R6923 on the board?

              I thought removing this resistor is isolating the circuit from the rest of the board, and since it seems to be working properly now, the issue must be part of the circuit after R6923 pulling the voltage down?

              I may be completely wrong as I think this may be the first macbook board Ive worked on, so Im learning as I go.

              I will try remove the FB resisitors and test (they're so tiny Im afraid I will lose one lol).

              Oh wow 2nd in a couple of days, I must have missed that post, can you link me?

              Thanks for your help so far.

              Comment

              • mon2
                Badcaps Legend
                • Dec 2019
                • 13830
                • Canada

                #8
                Okay, so you think U6903 is defective even though after I remove R6923 off the board, pin 3 on D6902 seems to be normal and also pin 2 of L6900 shows the correct 3.4V, instead of the 2.2V I was getting with R6923 on the board?
                Missed that - my bad. Then this regulator is OK but if 2v2 then something is wrong. If you add R6923, the voltage tanks to 2v2? That is, under normal load, this rail should remain stable @ 3v42. Your FB resistors are fine - do not mess with those.

                Comment

                • mon2
                  Badcaps Legend
                  • Dec 2019
                  • 13830
                  • Canada

                  #9
                  820-00281 - Badcaps

                  Comment

                  • JasonC89
                    Member
                    • Apr 2023
                    • 17
                    • Ireland

                    #10
                    Originally posted by mon2

                    Missed that - my bad. Then this regulator is OK but if 2v2 then something is wrong. If you add R6923, the voltage tanks to 2v2? That is, under normal load, this rail should remain stable @ 3v42. Your FB resistors are fine - do not mess with those.
                    No worriee, just making sure in my thinking. Yes, if I add R6923 back, voltage drops back to 2.2V? Something must be pulling it down?

                    Ive checked resistance again with R6923 removed and get over 500k on pin 2 so no sign of anything short that side.

                    Comment

                    • JasonC89
                      Member
                      • Apr 2023
                      • 17
                      • Ireland

                      #11
                      Ive done a bit more testing on U6903 just to check voltages coming out.

                      With R6923 in place :
                      1. P3V3G3H_VBST = 4.88V
                      2. PPVIN_G3H_P3V3G3H = 4.14V
                      3. P3V3G3H_LX = 2.23V
                      8. P3V3G3H_BIAS = 4.13V
                      9. P3V3G3H_FB = 0.66V
                      10. PM_EN_P3V3_G3H_R = 4.91V

                      With R6923 removed :
                      1. P3V3G3H_VBST =7.63V
                      2. PPVIN_G3H_P3V3G3H = 5.01V
                      3. P3V3G3H_LX = 3.4V
                      8. P3V3G3H_BIAS = 4.98V
                      9. P3V3G3H_FB = 1.02V
                      10. PM_EN_P3V3_G3H_R = 4.99V

                      Not sure how significant these are but just thought I would test both with and without R6923 so it can be compared. ​

                      Comment

                      • mon2
                        Badcaps Legend
                        • Dec 2019
                        • 13830
                        • Canada

                        #12
                        I would consider to replace this regulator and also D6902. If practical, start with D6902 and test again. It appears that this regulator wimps out upon applying a typical output load.

                        Comment

                        • JasonC89
                          Member
                          • Apr 2023
                          • 17
                          • Ireland

                          #13
                          Originally posted by mon2
                          I would consider to replace this regulator and also D6902. If practical, start with D6902 and test again. It appears that this regulator wimps out upon applying a typical output load.
                          Yeah I may just replace the diode.
                          ​​​​​​I do actually recall it getting hot (using thermal camera) when I first started testing. Found a low resistance on pin 3, that went away when I removed one of the 2 caps on the line.

                          Jow I just need to find a replacment as I have no macbook boards, but plenty of windows laptop donors.
                          ​​​​​​

                          Comment

                          • mon2
                            Badcaps Legend
                            • Dec 2019
                            • 13830
                            • Canada

                            #14
                            The diode is a jellybean dual common cathode type. For testing, remove this diode and bridge pins # 1 to # 3 on the PCB. Then test again to see if the voltage is stable with the load.

                            Consult the datasheet of this diode to note the pinout for this bridging.

                            Comment

                            • JasonC89
                              Member
                              • Apr 2023
                              • 17
                              • Ireland

                              #15
                              Originally posted by mon2
                              The diode is a jellybean dual common cathode type. For testing, remove this diode and bridge pins # 1 to # 3 on the PCB. Then test again to see if the voltage is stable with the load.

                              Consult the datasheet of this diode to note the pinout for this bridging.
                              Okay I'll try this when I'm back working on it in the morning.

                              Thank you 🙏

                              Comment

                              • JasonC89
                                Member
                                • Apr 2023
                                • 17
                                • Ireland

                                #16
                                Originally posted by mon2
                                The diode is a jellybean dual common cathode type. For testing, remove this diode and bridge pins # 1 to # 3 on the PCB. Then test again to see if the voltage is stable with the load.

                                Consult the datasheet of this diode to note the pinout for this bridging.
                                Unfortunately still the same, which I thought it may be as I was thinking about it last night. I removed diode previously and still got the drop on pin #3 until I removed R6923.

                                I removed the diode again and ran a wire from pin #1 to pin #3, plugged in charger and I'm still only getting 5v. Pin #3 on D6902 is still getting pulled to 4v, resulting in only 2.2v on R6923.

                                Could it still be the regulator?

                                Could 3.4v be injected on R6923 to see if we get 20v on the charger, or is that risky?

                                Comment

                                • JasonC89
                                  Member
                                  • Apr 2023
                                  • 17
                                  • Ireland

                                  #17
                                  Anything else you suggest mon2 before I send this out?
                                  Thanks

                                  Comment

                                  • mon2
                                    Badcaps Legend
                                    • Dec 2019
                                    • 13830
                                    • Canada

                                    #18
                                    What is the exact voltage of PPBUS_G3H ?

                                    With no power, what is the resistance to ground (not diode mode) of PPBUS_G3H @ F7000 / F7001 (check both sides).

                                    Comment

                                    • mon2
                                      Badcaps Legend
                                      • Dec 2019
                                      • 13830
                                      • Canada

                                      #19
                                      Could 3.4v be injected on R6923 to see if we get 20v on the charger, or is that risky?
                                      Given that there is no short on this low current rail, you could consider using your DC power supply and limit the current of your external power source to 500mA and inject as you are considering @ R6923 (without R6923 installed). This will confirm that U6903 is defective since it wimps out upon attaching the downstream (consumer side) load.

                                      Comment

                                      • JasonC89
                                        Member
                                        • Apr 2023
                                        • 17
                                        • Ireland

                                        #20
                                        Originally posted by mon2
                                        What is the exact voltage of PPBUS_G3H ?

                                        With no power, what is the resistance to ground (not diode mode) of PPBUS_G3H @ F7000 / F7001 (check both sides).
                                        It's 2.2V when R6923 is on the board.

                                        I'll double check the resistance when I'm back.

                                        (I did notice that when testing one of the left side type c port, the voltage dropped from 2.2v down to 1.7V. I get 2.2V on R6923 on from the other 3 ports.

                                        Comment

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