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A2442 TOUCHID NOT WORKING

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    #1

    A2442 TOUCHID NOT WORKING

    I have an issue with a Mac A2442 , that had initially a short circuit on Q5800 after replacement it turn on without any other issue, only finger print not working. I follower the post " MacBook Pro M1 2021 A2442 Touch ID stopped working" by measuring in diode mode all SPI seems ok, but when checking for voltage i notice something strange regarding PP1V2_S2.

    The chips UT620, UT520, UT540 are powered by PP1V2_S2 (according schematic and board view), this voltage is missing, and when I check continuity with PP1V2_S2 rail, found that it is not connected to it. Compared on another similar board same thing.

    Is it a schematic error ? I doubt that trace issue can happen in both (the other one has a CPU issue).

    I am missing also the TOUCHID_PWR_EN that comes from CPU, it shows 1.2V sometimes for few seconds.

    So I am little bit lost now, is it a trace issue or CPU not having all condition to trigger the enable ?
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    #2
    Check the voltage to ground on L8280 = PP1V2_S2 (BUCK8).

    Comment

      #3
      PP1V2_S2 (BUCK8) is present, when I mesure were it should be it is there, UT620, UT520, UT540 PP1V2_S2 not present and TOUCHID_PWR_EN not present

      As I mentioned the mac is working fine, only the fingerprint is not. I did a DFU restore didn't solve it

      Comment

        #4
        What is the 820-**** number of your logic board? There are 2 versions of this chassis.

        Comment

          #5
          It's 820-02098

          Comment

            #6
            Remove all power. Meter in resistance mode. Touch your meter probes together and you should have ~0R ohms.

            Now check the resistance from CT540 (see attached) to either side of L8280 coil.

            From the schematic and BV, there must be ~0R ohms resistance between these 2 points of interest.

            Otherwise, you have a PCB trace break and UT540 is not being powered.

            Click image for larger version Name: power_rail.png Views: 0 Size: 104.3 KB ID: 3614453

            Comment

              #7
              I am getting mega ohm measurements between L8280 CT540 and on UT620, UT520.

              it sound like trace breaking, but how is it possible to have the exact same resistance measurement and diode mode measurement on a another 820-02098 board ??

              Comment

                #8
                I just figured out that it is a board delamination issue of the segment between UG400 and UT540. The resistance go to zero just by pressing down this area.

                Seems that it is very sensitive in this area because I have took out and back UG400 on both boards for troubleshooting purpose.

                thanks mon2 for your help.

                Comment

                  #9
                  Just for update, soldering a jumper wire to the nearest PP1V2_S2 ( pin 2 Non stuff UG280) and pin 1 RT621 solved the problem, fingerprint is now working fine.

                  thanks again

                  Comment

                    #10
                    Interesting. Good case and closure.

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