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    No Trackpad a1278

    Hi I'm new to the forum and hoping to learn a bit along the way.
    I recently purchased an old water damaged macbook to help me learn a bit more about electronic, schematics and board views.

    I have managed to get around a lot of problems. I have it turning on and even charging now. The only problem Im seeing at the minute is the trackpad.

    I just can't understand the trackpad circuit.
    I finally realised I'm missing the 18.5v on the Trackpad connector J5800, which lead me to U5701 which has power but I noticed pin 21 was missing 18.5v.

    USB_TPAD_P was present at R5701=3.1v
    But
    USBTPAD_N was 0v

    Which somehow lead me to U5805
    which is missing 5v power in the entire region.

    This is were I'm getting really confused I think I'm supposed to be getting power from L5800 and C5800 which are both missing from my board.

    I was starting to think somebody removed them but the pads look normal, OK some corrosion but doesn't look like parts were removed.
    I then managed to find photos online of my exact model and they are all missing these parts too, but the schematics and board views for my model all show these parts and I really can't understand how U5701 is supposed to function without the 5volts that would be fed by the missing components.

    My board is the 2012 i7. 2.9GHz

    A1278 820_3115_B

    The only schematic I can find is the
    A1278 820_3115_B MLB, J30

    But this clearly is the wrong schematic as at a glance is missing the following components. I have a feeling its just the i7 versions that have a different layout.

    Anyway I would appreciate if anyone could explain this to me.

    Thanks

    All missing
    R7803
    C5800
    L5800
    R4515
    R5015
    R2704
    C7800

    #2
    Re: No Trackpad a1278

    There is an A and B variant of the 3115 board. Missing components are usually listed as NO STUFF in the schematic.

    You should always try another trackpad first, as they often get damaged by liquid or bulging batteries. You should have PP3V3_S4_TPAD, PP5V_S5_CUMULUS and PP18V5_Z2 present on the connector. The latter is generated by a boost converter U5805/L5801/D5802. These converters will shutdown if there's a short, so check impedance on the output. Filter caps or the trackpad itself could cause a problem. I have seen a crook U5701 cause a dead trackpad, however that was one I fitted off Aliexpress. It's unlikely to be this IC though, these rarely fail and any issues usually are poor solder joints on the QFN.
    Last edited by reformatt; 03-01-2022, 08:45 AM.

    Comment


      #3
      Re: No Trackpad a1278

      Firstly thanks for the fast reply.
      My board is marked as the B version
      I never new about the NO STUFF marking, that's very helpful, but unfortunately that isn't mentioned on the components im missing.
      I did try replacing the flex already but when it didn't work I done a bit of digging only to find I was missing the 18.5v on the motherboard flex connector J5800, I will attach an image displaying the voltages im getting, along with a screen shot of the schematic im working off.

      I do have PP3V3_S4_TPAD on pin 22
      Im missing PP5V_S5_CUMULUS on pin 18
      Im missing PP18V5_Z2 on pin 21


      “The latter is generated by a boost converter U5805/L5801/D5802”

      This is the region of the board that has no power and is responsible for the 18.5v that im missing at the flex connector J5800. All three of the components you mention have no power.

      PP5V_S5_PAD never gets over to that area of the board to give power to U5805 or the resistor beside it R5805.
      From what I see the only thing that is stopping it is two missing components that show on the schematic L5800 and C5800.
      If they were present it would bring power right into U5805.

      I cannot understand why this model is missing them, but as I said before I can see photos online with new boards missing the same components so they must not be needed and I have a broken trace somewhere.


      I don't know about u5701, all I know is he is getting fed 3.3v on pin 49
      But missing USB_TPAD_N at R5702 and pin 21


      Finally how do I go about checking the impedance on the output, sorry im totally new to this, do I need a special meter ?.
      Attached Files

      Comment


        #4
        Re: No Trackpad a1278

        I do have a few 3115 boards lying around in my donor pile. So I looked and L5800 is not populated so just ignore that.

        You should however have 5V on R5805 as it's sourced off PP5V_S5_LDO (refer pg 8 of schematic). Being a S5 rail, this should always be present. It comes off U7200 pin 17. If the system is booting, I can't imagine this rail being absent so check continuity from that pin to R5805. You might have a corroded via or track.

        Once you have that sorted, PP18V5_Z2 will require an enable (high) to pin 5 of U5805. This enable appears to come from the trackpad itself, so would rely on PP3V3_S4_TPAD being present on J5800 and a functional trackpad.

        Impedance = resistance. Use a meter in ohms mode.

        Comment


          #5
          Re: No Trackpad a1278

          Again thanks for the fast reply.
          You were right I did have 5v on U7200 pin 17 and no continuity between R5805 and U7200 pin 17.

          So I ran a 0.1mm wire and now the trackpad seems to be working, but I haven’t really had time to fully assemble and test.

          Im actually surprised it was just one wire, as I thought a few of the voltages on flex connector J5800 were a bit erratic.

          Also I presumed I should be measuring 18.5v on pin 22, but as you said that needs to be enabled first and then powered by the trackpad itself.

          Do you think the 0.1mm wire is big enough or should I change to something bigger ?

          One final thing, is there any chance you could send me a photo of what the area around L5800 and C5800 should look like, that is the worst area of my board, the pads are gone but since there was no components present I didn’t think they would cause a problem.

          But that seems to be the path that U7200 pin 17 travels to get to R5805. I still can’t understand how it actually gets to R5805, yes its 99% of the way but with them missing components I can’t understand how its suppose to get through the gap where L5800 and C5800 are missing, to deliver the 5v to R5805.
          Maybe a photo might help.

          Thanks again, no way I would have figured it out without your help.

          Comment


            #6
            Re: No Trackpad a1278

            Apple boards often have via's hidden under component pads so corrosion cause open circuits. L5800/C5800 pads are at the same height as U7200 on the opposite side of the board so if they're missing this is likely the cause of the fault.

            Sometimes you can rebuild the pad if the via is still visible in some fashion with jumper wire and conformal coating. 0.1mm is fine, but on the bigger end of the scale in board repairs.
            Last edited by reformatt; 03-03-2022, 05:23 PM.

            Comment


              #7
              Re: No Trackpad a1278

              So do you recommend that I change to a larger wire?
              I do have a larger size enamel coated wire, but its a good bit bigger and won't fit through the via hole, but that's not a problem.
              Do you have a PayPal account, would like to buy you a drink.

              Thanks

              Comment


                #8
                Re: No Trackpad a1278

                LDO outputs are usually rated at 100ma, so even 0.02mm wire would work. You'd only need something substantial say in a power MOSFET situation feeding lots of current.

                Comment


                  #9
                  Re: No Trackpad a1278

                  Hi I finally got the a1278 fully working tonight.
                  I had the trackpad working but when I took your advice and changed the enamelled wire to a more appropriate size it stopped working.
                  Then in fault finding I shorted another chip and could no longer get green light.
                  Then got back to green light but still no trackpad so ended up buying a doner board and replacing U5805 and everything finally working.
                  But unfortunately I now have a bigger problem.
                  The previous owner says they removed the iCloud from their account but I don't think they did it correctly and to make it worse they don't remember the admin password. I have access to the computer, but all I want to do is wipe it and use for myself.
                  Do you think there is a way to wipe the computer ?, The owner is genuine as they managed to unlock an iPad I purchased along with the macbook.
                  They say they removed the macbook too but on the computer I can see how many gb they are using in iCloud so looks like its still linked to there account.
                  I will attach a photo. Is there anyway out of this for me. I have spent more than the computer is worth trying to fix but it wasn't really about the money, Just trying to learn, but it would be nice to be able to use it.
                  As nice as the previous owners are I think they have had enough of me and say they can't do anything more.

                  Im afraid to try wipe the computer as I could end up being completely locked out, at least at the minute the computer logs straight in not asking for any passwords.


                  Thanks again for your help.
                  Attached Files

                  Comment


                    #10
                    Re: No Trackpad a1278

                    There is no activation locking on anything prior to the advent on the T2. So you can just wipe it. You can just go to recovery console (CMD+R on boot), format the drive, and reinstall MAC OS. That'll install the same version it shipped with though (which will be ancient).

                    Since you have a 2012 MAC, you can install Catalina (or go higher if you want to use the Core Legacy Patcher). Not sure what MAC OS you are on, but I usually get the full installers via softwareupdate in a terminal window (older versions of MAC OS may not support this, not sure). For example:

                    softwareupdate --fetch-full-installer --full-installer-version 10.15.7

                    (This will download the Catalina full installer to your Applications folder).

                    Create your USB installer using the createinstallmedia script in the resources folder of the installer (https://support.apple.com/en-au/HT201372). Hold OPTION on bootup and select your Catalina USB installer and off you go.
                    Last edited by reformatt; 05-08-2022, 02:31 AM.

                    Comment


                      #11
                      Re: No Trackpad a1278

                      That's great news, I would be happy if I can get to Catalina without too much hassle. I would be afraid to go higher incase I bricked it or maybe the computer might not be able to handle it and be too slow.
                      Thanks again, I really was convinced I was in trouble. 👍👍👍

                      Comment


                        #12
                        Re: No Trackpad a1278

                        I can see Find My mac is still enabled. Do you think this will disable that too ?.

                        Hard to believe wiping the hard disk will disable find my mac.
                        Attached Files

                        Comment


                          #13
                          Re: No Trackpad a1278

                          Find my MAC can become an issue if they've enabled lost mode. In that event, it will put a password on the EFI when it connects to the net. I'm not really sure about the status after removal, since I just wipe systems without looking. If they have removed it, don't think it should be an issue. Firmware locking disables OPTION key, PRAM reset etc if that has already happened so check that first.

                          If you do encounter it, it's fairly easy to circumvent if you have a SPI programmer. You have a donor board you said, so you could use U6100 from it or the serial number. Think in this model you need to clean the ME region though if you transfer the chip.

                          Comment


                            #14
                            Re: No Trackpad a1278

                            I will give the previous owner a few days to try turn off Find My Mac.
                            If he doesn't I will just try and wipe it and see what happens.
                            Im afraid Im totally new to this and had to google a lot of the terms above.
                            Worst case I will have to bring to a professional.
                            As for lost mode that shouldn't be activated as he sold it to me.

                            The options button is currently working if that's what you mean.
                            As for the donor board its an older model so not sure if U6100 would be compatible, lucky U5805 was.

                            I don't know where you learn this stuff. Very interesting.

                            Comment


                              #15
                              Re: No Trackpad a1278

                              I meant OPTION on boot. It's all easily circumvented by dumping the BIOS and editing it. Plenty of resources here on how to alter serial number, remove password, clean the ME etc. There are others here that will do it for you if you ask nicely enough. You just need a programmer, like the CH341.

                              Comment


                                #16
                                Re: No Trackpad a1278

                                Thanks I will have a read up on it anyway. I do feel a bit out of my depth and cant believe I got this far on my first board. Plenty of mistakes, a lot of luck and a lot of help along the way. ������

                                Comment

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