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MacBook A1707 - low batt sign displayed then shutdown - but battery voltage is ok!?

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    #1

    MacBook A1707 - low batt sign displayed then shutdown - but battery voltage is ok!?

    Hi fellow repair gurus,

    Liquid damaged A1707 was stuck on 5V. I replaced corroded CD3215 and SMC now successfully raises voltage to 20v.

    The fans spin, the screen comes on and displays a "low battery" sign before the machine shuts down.

    After that the screen and fan stays off but PPBUS_G3H continue to toggle every 4-5 secs between
    • 11.4v (and 170mA current draw on usb-c power meter)
    • 12.6v (zero current draw)


    The toggeling occurs when battery is connected but regardless if external usb-c is connected or not. It seems it's trying to start a charging cycle, but then gives up and shuts down..?

    If I disconnect the battery and boot from USB-C only then PPBUS_G3H is stable at 12.6v during and after low-bat sign on screen. (AFAIK these macs need a working battery to boot)

    I'm confused and don't know how to proceed because

    • if it is a short I guess it wouldn't be able to establish all rails and display anything on the screen?
    • if it is bad battery/battery board it wouldn't be able to boot on battery only and display the sign on screen?
    • ISL6259 seems ok since PPBUS_G3H is ok (albeit dropping to 11.4 volt periodically as described above)


    Any clues would be great!

    Cheers,
    Erik

    Tags: None
    #2
    Re: MacBook A1707 - low batt sign displayed then shutdown - but battery voltage is ok

    Hi. See attached.

    Meter in DC volts mode.

    With extreme care, check the voltage to ground of the SMBUS (aka I2C) communication lines (SDA & SCL).

    on this logic board:

    SMBUS_SMC_5_G3_SCL
    SMBUS_SMC_5_G3_SDA

    The logic board will extract battery details using this 2 wire communication.

    What voltage do you measure on each of these lines ?

    Red meter probe on SDA; black meter probe to ground.

    Then repeat with SCL & ground.
    Attached Files

    Comment

      #3
      Re: MacBook A1707 - low batt sign displayed then shutdown - but battery voltage is ok

      That's a great tip, thank you.

      I scoped the SCL and SDA lines and they look perfectly fine. The SMC is obviously trying to speak to the battery.
      I did these measurements with the battery disconnected as I had to take the board out to get to the test points.

      SCL line with clock bursts


      SDA line with data


      Should I try to do the measurements while battery is connected? I mean to determine if the battery answers? I have the i2c bus option on my scope, although I'm not sure how I would determine that battery speaks...

      There were some signs of damage on the connector at the end of the small flat cable coming from the battery board, I guess there are i2c lines among these. But it looks ok in the microscope. Also, ohming the leads from the cable over to the PCB shows continuity is ok.



      Any other clues greatly appreciated

      Comment

        #4
        Re: MacBook A1707 - low batt sign displayed then shutdown - but battery voltage is ok

        Locate and review the high side and low side charging mosfets linked to the ISL charger IC.

        Respectively, there will be a current sense resistor for the rail produced by these pair of mosfets. The current sense resistor then being monitored by the isl charger IC via a positive and negative side of the resistor.

        Confirm that the feedback loop resistors are not damaged. If the parts are corroded or missing, the isl will sense incorrectly that too much current is being drawn and shut it all down.

        That battery cable looks nasty. Are you sure it is ok?

        Comment

          #5
          Re: MacBook A1707 - low batt sign displayed then shutdown - but battery voltage is ok

          Hi,

          The current sense resistor R7060 and the mosfet Q7065 looks ok. The resistor is 0.005 ohm, which I have no way of veryfying. But it measures as a short on my DMM so it's probably ok. Also, the mosfet passes on 12.6v to the battery connector after a few seconds, as expected.



          Following up on your comment about the connector I took out the battery board and flipped it (kind of hard because of the cables to the battery). And indeed I found some corrotion on the back-side, where the flat cable is connected to the battery board



          I cleaned and ohm'ed between the test points on the board and the other end of the connector, and they are continuous.
          Perhaps the logic on the battery-board has failed after the liquid damage. It's difficult to test because most of the board is in epoxy.

          Anyhow, I just looked at this video from one of Louis Rossman's guys doing a repair on an A1707. And I see that he is actually booting the machine with the screen connected but without the battery.
          https://youtu.be/EUWmqucOkZk

          When I boot the computer without the battery connected I still get the "Low battery" sign. I thought this model could not start without a battery, but obviously I was wrong.

          So I guess something else than the battery must wrong. In the same video he also changes the MUX, saying that it almost almost fails in these scenarioes.
          Do you believe a failed mux could cause a Low power sign to be shown on the screen?

          I will try to boot now with battery but without screen connected.

          Thanks for your comments so far, greatly appreciated

          Comment

            #6
            Re: MacBook A1707 - low batt sign displayed then shutdown - but battery voltage is ok

            Finally some progress.

            The machine now starts normally after cleaning some liquid damage I noticed on the keyboard connector

            However, it still doesn't charge the battery.

            • PPBUS_G3H stays rock solid at 12.456v, and passed on to Source of P-channel Q7065 via sense resistor
            • ISL9239 tries to start charging by pulling down Gate of Q7065 to pass the voltage to Draing, thus to the battery connector
            • The Drain/battery voltage output of Q7064 goes to 12.456 volt for a brief moment, then drops to between 8-10 volt (varies it seems). This continues to cycle like this.
            • The voltage drop across the sens resistor R7060 is 3mV while Q7065 is on, implying a current draw of 0.005/0.003 = 600mA , which is ok.




            If I disconnect the battery the Q7065 passes the Source voltage of 12.456v and stays there.

            To my understanding either the battery is toast and doesn't receive charge, or the ISL9239 has partly failed.

            Will try to replace ISL9239. The ones I got are from Ali, fingers crossed.

            If not successfull I will order a battery in a couple of days, but would appreciate any comments to my analysis.

            cheers.

            Comment

              #7
              Re: MacBook A1707 - low batt sign displayed then shutdown - but battery voltage is ok

              If the battery does not change its charge level after a period of time then the battery should be replaced.

              What is the reported charge on the battery in the desktop? If the charge does not climb then test with another but known good battery.

              Can you extract the number of charge cycles, etc out of the battery?

              Suggest that before replacing the ISL which appears to be ok at this time.

              Comment

                #8
                Re: MacBook A1707 - low batt sign displayed then shutdown - but battery voltage is ok

                What is the reported charge on the battery in the desktop?
                I will need to get the password from the owner for that, will try tomorrow.

                The battery is labeled as shown below. Not sure why both 13.05 and 11.40 Vdc is listed.


                When I measure the cell voltages directly on the battery board (not the connector, as that is controlled by fets), it says 11.3 volt, so I believe the cells are ok at least.

                Can you extract the number of charge cycles, etc out of the battery?
                I don't have tools for that. However, the machine almost looks like new so I don't belive it has had heavy usage.

                I read in the Repair Wiki that SMC also sometimes is a problem when battery is not recognized.
                https://repair.wiki/w/A1707_2016-201...ar_MacBook_Pro

                But since the ISL chip is opening the mosfet to pass charging voltage to battery I don't see how that can be the issue here...

                I have ordered a new battery, should get it in 1-2 days. Will keep you posted.
                Thanks for your help so far.

                Comment

                  #9
                  Re: MacBook A1707 - low batt sign displayed then shutdown - but battery voltage is ok

                  You can view the stats on the battery as follows:

                  https://support.apple.com/en-ca/HT201585

                  The battery in the pic is not an original Apple.

                  Do check if the battery mosfet is ok. Remove all power.

                  Meter in resistance. Check the resistance across the mosfet pins:

                  Source & drain
                  Source & gate
                  Gate & drain

                  Post each measurement.

                  Comment

                    #10
                    Re: MacBook A1707 - low batt sign displayed then shutdown - but battery voltage is ok

                    Thx, will try the System Info thing if I get the login

                    Mosfets readings:

                    Source & Drain : 230k
                    Source Gate : 390k
                    Gate & Drain : 452k

                    And btw, the cell beneath the t-pad cable looks more Apple-like, perhaps it's autentic after all

                    Last edited by kurland; 10-25-2022, 02:08 AM.

                    Comment

                      #11
                      Re: MacBook A1707 - low batt sign displayed then shutdown - but battery voltage is ok

                      Looks like the battery was the problem. I got the new battery today and it's charging nicely at 3+ amps. Thanks for your help, I learned alot.

                      Now I just need to get the old one out safely, think I will try the waxed thread method that Paul Daniels did in a video.

                      Cheers!

                      Comment

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