A1708 peculiar bms problem.

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  • 100FIX
    New Member
    • Jul 2024
    • 5
    • Nigeria
    #1

    A1708 peculiar bms problem.

    Hi, I have a mbp a1708 2017 that I am trying to fix.

    (1.) It turns on fine on ac power when bms flex is unplugged.

    (2.) I noticed when battery & charger is unplugged and reconnected, it turns on only after a few minutes but doesn't stay on battery power i.e. it turns off as soon as charger is unplugged and doesn't turn on until (2.) is repeated. During this time, health information and charging information are displayed and normal and battery charges but laptop turns off as soon as charger is disconnected.

    I have reballed u7000, problem persists.

    What could be the problem?
    Tags: None
    • mon2
      Badcaps Legend
      • Dec 2019
      • 13894
      • Canada
      #2
      Check the voltage to ground of each pin on the battery connector or BMS flex when they are connected. Appears that your BMS flex is defective.

        Comment

        • 100FIX
          New Member
          • Jul 2024
          • 5
          • Nigeria
          #3
          Originally posted by mon2
          Check the voltage to ground of each pin on the battery connector or BMS flex when they are connected. Appears that your BMS flex is defective.
          I have tried with a known working flex and battery, same result.

            Comment

            • mon2
              Badcaps Legend
              • Dec 2019
              • 13894
              • Canada
              #4
              Measure the voltage of each pin on the battery connector. The TVS ESD diodes that are on the smbus lines are of concern (SDA / SCL).

                Comment

                • 100FIX
                  New Member
                  • Jul 2024
                  • 5
                  • Nigeria
                  #5
                  Voltage on sda, scl on mobo side reads about 3.5v. For battery side, I tested with working battery from similar laptop already.
                  I removed the tvs diode on sda/scl/gnd already (awaiting arrival of replacement part). Issue persists.

                    Comment

                    • mon2
                      Badcaps Legend
                      • Dec 2019
                      • 13894
                      • Canada
                      #6
                      Not at my desk and about to enter the Netflix zone. Remove all power. Meter in resistance mode. Measure the full path resistance of the battery charge current loop. We need to know and compare the measured resistance against the schematics. If the resistance varies then this is an issue. Share the resistance. Since you cannot reach the hidden balls of the isl charger ic, measure at one of nearby caps on the SRP / SRN contacts.

                        Comment

                        • mon2
                          Badcaps Legend
                          • Dec 2019
                          • 13894
                          • Canada
                          #7
                          Measure the resistance across capacitor C7020. This is to determine the resistance seen by CSOP / CSON balls of the charger IC. For a normal unit, this resistance should be ~2 ohms.

                          Click image for larger version Name: battery_charge_current_sense.png Views: 65 Size: 225.4 KB ID: 3310899

                            Comment

                            • 100FIX
                              New Member
                              • Jul 2024
                              • 5
                              • Nigeria
                              #8
                              Originally posted by mon2
                              Measure the resistance across capacitor C7020. This is to determine the resistance seen by CSOP / CSON balls of the charger IC. For a normal unit, this resistance should be ~2 ohms.

                              Click image for larger version Name: battery_charge_current_sense.png Views: 65 Size: 225.4 KB ID: 3310899
                              Sorry for the late reply. Had a problem with my meter test probes, all the values were off, so I had to get a replacement.
                              I have checked values on c7020, it is exactly 2ohms. Do you suggest i replace u7000?

                              (I have also recieved the replacement tvs diodes and installed it.)

                                Comment

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