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macbook A1707 Board (820-00928) (Board Schematic 820-00281) U3905 BGA Corroded pin 21

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    #1

    macbook A1707 Board (820-00928) (Board Schematic 820-00281) U3905 BGA Corroded pin 21

    I'm trying to get this A1707 macbook working. There was some liquid damage under U3905 and corrosion around the Tantalum capacitors C3502 C3504.
    Removing the U3905 (PN66VEU3-A101D004) shows that the pad is somewhat damaged. I'm not reading continuity between pin 21 and the filter cap C3919.

    Researching that part shows that its an NFC chip, which makes me go huhhh? And Why??? Why does a macbook even have and NFC chip, and if I just leave it out will it cause issues?

    If I can get away with just replacing the tantalum caps and ignoring the NFC chip that would be great since It appears the pad was on top of a via, and I'm not certain how to repair that.
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    #2
    I was able to boot into a clean OS leaving the NFC chip off; however, there appears to be something wrong with the Touch bar, giving me the dreaded can't install critical update error.

    I'm assuming it has nothing to do with the touch bar the Section of the schematic it's in is referred to as "Stockholm".

    Comment

      #3
      There's no NFC function in the MAC, however some functions of it are needed for the T1 (as it's a CPU design borrowed from the iPhone). Critical update refers to the firmware for the T1 CPU and this handles things like Touch ID and Touchbar etc. You'll have to run a jumper to the broken pad 10,21 to fix and reinstall the IC.

      Comment

        #4
        Originally posted by reformatt View Post
        There's no NFC function in the MAC, however some functions of it are needed for the T1 (as it's a CPU design borrowed from the iPhone). Critical update refers to the firmware for the T1 CPU and this handles things like Touch ID and Touchbar etc. You'll have to run a jumper to the broken pad 10,21 to fix and reinstall the IC.
        Interesting that the part number shows up as being an NFC device. I wonder who at apple thought "Stockholm" was a good choice for controlling those components. We love our fruity captors.
        I will try to find a nice fine wire for making a jumper. Very fortunate it is on the edge of the BGA.

        Do you know if that chip is paired to match serial numbers?

        Thank you very much.

        Comment

          #5
          About the only connections to it is via SPI from the T1. Likely they couldn't bother reworking the whole CPU to omit it as it doesn't appear to go anywhere else. Dunno, but the fact that its on the board means it's needed for something. AFAIK, the only thing that is serialized on T1 one machines is Touch ID and that's linked to the T1 itself and it's ROM.

          Comment

            #6
            Originally posted by reformatt View Post
            About the only connections to it is via SPI from the T1. Likely they couldn't bother reworking the whole CPU to omit it as it doesn't appear to go anywhere else. Dunno, but the fact that its on the board means it's needed for something. AFAIK, the only thing that is serialized on T1 one machines is Touch ID and that's linked to the T1 itself and it's ROM.
            BTW not sure what you mean by broken pad 10, 21. It's pad 21 It's a 3V rail and pad 44 appears to be the same rail. Not sure if its redundant power connection. The problem I'm having right now is I only have 36 AWG wire and it's still to thick to create a trace from C3919 to pad 21. I could try to make a groove to accommodate wire, but worried about damaging a layer. The trace for pad 44 is exposed but I'm not sure how important the connection to that filter capacitor is, I did run the jumper there just in case.

            I accidentally took out R5851 and C3915 in the process, so now I need to wait for those parts before testing.

            BTW has anybody make any tutorials on repairing a BGA pad, at least one on the perimeter? I know Rossman recommends using battery wire from old macbook pro batteries for extra fine work.

            Thanks for the help!

            Comment

              #7
              Yes, review this video - Wylie started this repair BGA ball pad kit:

              https://www.youtube.com/watch?v=I_6xZVY7sFM

              Mobile sentrix (USA / Canada) sells them.

              https://www.mobilesentrix.com/wylie-...-soldering-lug

              Comment

                #8
                Having an elderly moment and looking at the wrong chip, so yes only pin 21 needed. As it's at the edge of the chip, you can just run small jumper and tack it down with conformal coating to hold it in place. This is what I do with other chips like the backlight IC on airs when the feedback pin is corroded.

                You can use 0.01 or 0.02 Mechanic jumper wire. It's enameled though so can be a PITA to tin when it is very short like that. I have used a single strand from my desoldering braid when it's only a very short jumper and doesn't need to be insulated. It is a hack, but the resistance of such a short wire is negligible.

                If you want to look at the Wylie style pad repair, check out some of the videos on the KrisFix or NorthWest Repair YT channels, where they fix ripped pads on the edges of GPU's. They do make it look rather easy.

                I also recommend the Mechanic KA-11 tweezers for the finer work with jumpers, and where components are closer together. I haven't have much success with the Titanium 'flyline' tweezers myself, the tips always seem to deform and bend for me. The KA-11 are ultra fine but are quite resistant to bending.

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                  #9
                  Thanks for the tips I will probably need to order another one of those chips just in case I killed it. It didn't seem like there was a nub of a trace under where the pad is, my biggest concern is there are other critical paths on a layer underneath that are now compromised, but I suppose I can just trace it out and see if any voltages are missing since it's just a 3v3 rail.

                  I just have some Wiha 7a SA-ESD right now They're pretty sturdy but maybe a bit CHONKY compared to the KA-11. I should probably pick up some finer tips straight tweezers.

                  Comment

                    #10
                    Originally posted by reformatt View Post
                    I also recommend the Mechanic KA-11 tweezers for the finer work with jumpers, and where components are closer together. I haven't have much success with the Titanium 'flyline' tweezers myself, the tips always seem to deform and bend for me. The KA-11 are ultra fine but are quite resistant to bending.
                    Thanks for the tweezer recommendation, the KA-11 are sharp literally. I was able to repair that pad it certainly is receiving the 3.3V I put in a replacement chip and as far as I can tell the bga flowed well snapping itself into place with surface tension, annnnnd still gets the dreaded can't install critical update error.

                    Interesting things of note. If I don't power up the laptop with the battery disconnected first so I see the Low battery logo, then connect the library and power it up, the machine does a weird power cycle loop where it draws up to 1.4~1.5 A idles around .8A then goes to zero and cycles with this behavior.

                    It boots into the OS setup if I power first before connecting the battery. I'm still stuck at the critical update needed.

                    I don't know much about the history of this laptop, all the moisture stickers are red; however, there was only one tiny area of corrosion on the Stockholm chip.

                    Are there any signals I should try to observe from this chip?

                    I have no real way of knowing what the condition of the touch bar is my next step is to just try changing bodies and seeing if it's a bad touch bar.

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