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Strategy for Soldering Skills validation on fully working iphone 5s's.

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  • #16
    Thanks for that. Today I removed the FL29 (when a coil is preceded by FL does that mean filter?)that runs between one of the rear camera connectors and CPU. AP_BI_RCAM_I2C_SDA_CONN some sort or data line between Camera and CPU I assume.
    Removing that little guy produced a BIG problem... camera screen went black, no error messages nothing... like now you see it now you don't. Hot tweezer it back - everything back to normal! Next thing I'm going to desolder/resolder Chestnut. After that..... are there any signature failures for the iPhone 5s I can simulate? I did a full search on the logic board repair posts, page by page but didn't really come back with anything.


    • #17
      The 5s gets tristar failures, technician damage at FL11, digitizer connector technician damage, technician damage at sage, water damage at chestnut, and long screw damage causing blue screen of death. Sometimes short on a chestnut output after drop. Red screen of death which is often nand If not parts or water damage. Can’t think of anything else.

      5s as a current device that people are seeing a lot pre-dates this forum. There’s only one 5s that I can think of on this forum and it was Joe Bouvier’s.


      • #18
        Thanks for that. I removed and restored Chestnut. The result. A dimmed and inky looking picture (see pic)and no touch. What may I have done wrong?
        Attached Files


        • #19
          Look on the schematic and see what chestnut does. Do you think that no touch could have something to do with chestnut or not? Does chestnut have anything to do with image or not?


          • #20
            I already know Chestnut is a power IC. Not only does it supply power to image, it also supplies power to touch. (It does have a couple of lines going directly to Sage). There is a rather large external component it relies on to help it do it's job..... The board looks ok. I haven't knocked anything off, however, and nothing looks dislodged. I'm assuming whatever I did Chestnut did not like.


            • #21
              Right—so you have no touch and weird image after removing, Reballing, and replacing chestnut. So what’s the problem? It’s your chestnut job. Take it off and put on a new chestnut to eliminate reballing. At PBRS we don’t allow students to use reballed chips until they demonstrate that they can put new chips on the board.

              if you have no choice but to reball chestnut then reball it and check the chip on an angle before installing to be sure the balls are even. Also be sure the sides/corners have zero damage


              • #22
                Ok. Thanks for that. Today I worked on an icloud locked 5s.
                Before getting to work on it I confirmed that It boots ok.

                (1) has image and touch

                (2) WIFI is working

                (3) The phone charges

                (A) Today I changed the direction of the hot air. Previously I aimed it off the motherboard to the left. Unfortunately, whilst minimising the flow of hot air to surrounding components on the board, it also flowed in the direction of my tweezer holding hand(I'm left handed). Too hot for comfort! Now I aim it up over NAND into the direction of WIFI. Initially I felt fearful about 'destroying' these ICs so tried heat sinking NAND and WIFI with a couple of coins
                (see picture 1)

                I previously established that with an 8mm nozzle, 380 degrees 100 litre airflow I could remove the IC in 20 -25 seconds. Now, with the heat sinking, it was 40 seconds and Chestnut was still firmly soldered to the board. Conclusion the board (and Chestnut) needs to heat up and heat sinking stops this = heat sinking no good. At 40 seconds I got Nancy with the tweezers, pincered the IC causing a tiny chip.
                (see picture 2)

                (B) I took the board out and retested to make sure Chestnut still working. Image and touch OK. All good. Dismantled and minus the heat sinking got chestnut off in 20 seconds. A bit too soon as I sheared two balls in the process. See picture 3. I retested the board to make sure NAND still ok. Of course there was no image but If the USB ammeter shows normal current draws on prompt to boot I take it as a sign that NAND(and CPU) is still good.

                (C) I loaded the 3mm chisel tip of my Hakko soldering iron with leaded solder, fluxed up Chestnut and ran the iron over the top - 1 second. Balls cleaned and flattened instantly
                (see picture 4)

                (see next post for next steps)

                Attached Files


                • #23
                  (see previous post for first steps)

                  (D) I reballed with my standard tin stencil. It took very little time, max 15 seconds of hot air 360 degrees 10mm nozzle 100L airflow.
                  Iwas happy with the balls, See pictures 1 and 2

                  (E) Here is a video link showing how I soldered Chestnut on. 360 degrees 100L 8mm tip. 23 seconds on 1-2 seconds off 5 second reseat
                  And a view of the motherboard after soldering on (see picture 3)

                  First I tried booting from a fully assembled frame. Then with charge port flex, screen and battery only. No image. Current draw erratic, no longer following normal boot current draw.
                  I desoldered Chestnut (clean lift) See result (picture 4) My post mortem = no shorts

                  And after desoldering Chestnut this is the boot sequence of the motherboard(connected to charge flex & battery - plugged into USB. It looked normal to me and I take as a sign that NAND and CPU are in fact alive and well.


                  Summary and Conclusion:
                  Ok I know I did something to Chestnut but I don't think? it was my reballing technique. As I said before I did chip it whilst heat sinking at the end of applying heat however assembled it into a working frame immediately after and verified it as still working. Of course there's nothing to say that in it's chipped state it was vunerable and the further application of heat/soldering somewhere along the line killed it?

                  Next step, I think, is to try a fresh Chestnut(I'll take it off another previously verified working iphone 5s since killed) - no chip. technique as per posted video (No heat sinking) No pincer this time.

                  Attached Files


                  • #24
                    What you’re trying to learn is exactly what we teach at Practical Board Repair School. I think you would really benefit from coming to the course. You will have success instantly and learn thousands of tiny details that will make you look back on the process you’re going through now and cringe.

                    I can’t write down the art of Microsoldering and there’s a reason we do not attempt to do online training. You can’t teach people to ride a bike online.

                    These posts have turned less into troubleshooting questions and more of what feels like online training. It doesn’t work.

                    My only advice is stop trying to learn to reball at the same time that you are learning to change a simple chip. Eliminate that variable because you are consistently installing damaged chips on boards.

                    If you want to change chestnut, get a new chestnut.


                    • #25
                      Thanks Jessa,
                      I'm recooperating from a back injury which right now prevents me from travelling long distances. I've done a lot of reballing since my last post - as it turns out, it's not causing any problems I am 110% happy with it. When I did damage ICs,however, I did it trying to stick my tweezers down a gap that was too small. Silly.That aside lot's of good chestnuts(all reballs), I think I've done about 10 on five motherboards, The clearances are tight but I found ways around that. Time to move on. I've already done a heap of Tristars and a few Sages. I'm thinking maybe I should validate my skills on Baseband - it's underfilled on the 5s (I'm keen to work my QianLi sickle)- now there's a challenge! If I get it wrong I'm assuming I'll lose my signal bars - or more likely just get an endless searching message! What do you think?


                      • #26
                        Sticking down one's tweezers in too narrow gaps can have some devastating effects on ICs but I only really appreciated the damage once I saw it under the microscope! Chips off the edge - in this case delamination(see pictures). Ironically some of these ICs still kind of worked. In one case where I had image but lost touch I measured 4v for PN5V7_SAGE_AVDDN.
                        Attached Files


                        • #27
                          EMI shields….Skills validated…….Lessons learnt.

                          TAKING the shield OFF
                          1. Check for and remove any stickers holding the shield
                          2. Tweezer the shield ie hold the board by the shield(shield is facing up)
                          3. Choose largest nozzle size(9mm plus is good)Set hot air temp and air flow to maximum.
                          4. Aim nozzle close and straight down into the shield.
                          5. Let gravity do the work. Board drops away leaving the shield in tweezers
                          6. Do NOT exceed 45seconds (use a timer - if board not dropping away at 45 seconds, STOP, cooldown, re try).

                          PUTTING the SHIELD back on
                          1. Use hot air NOT soldering iron!
                          2. Don't waste time , tinning joints, applying extra flux etc - unnecessary!
                          3. Just hold the shield in place to the board with tweezers and apply hot air as before ie largest nozzle straight down into the board
                          4. If it's a large shield may have to do in sections. ie stop, cool down move to next part
                          (Noted Previously soldered part does not unstick while tweezering and working on next part -- it holds).
                          The whole process done correctly takes no more than a few minutes.

                          Board reassembled into frame. All functions tested fully working. Skill validated.


                          • #28
                            Iphone 5s no 5 IOS 9.3.2
                            NOTE This phone was a working phone tested and confirmed fully working prior to dismantling & commencing this exercise as part of soldering skills validation
                            Initially desoldered, reballed, resoldered chestnut BUT pincer damaged the IC during removal (small chip in the corner)causing Partial loss of function ie had image but no touch. So I stole chestnut off an iphone 6 donor board and soldered it on. Image and touch restored BUT, upon full reassembly and retest.

                            (1) In Settings ->Touch ID & Passcode-> Add a fingerprint disabled
                            (2) Phone RF connection - NO signal bars, Stuck on searching and then No Service
                            Under General Settings-> About->Network Not Available. Still has an entry for Service Provider but not sure if this is a caveat from when it was working before the validation exercise.

                            I have double tested No 5 motherboard in two separate frames double testing all antenna connections are firm and sound - same result (1) and (2), I re validated another fully working phone 5s - No 7 in one of these two frames(No 7 not yet worked on) confirmed still fully working. I can only conclude that motherboard No 5 is damaged. COULD (1) and (2) be feasible(side effects?) damage caused from working on chestnut?