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iPhone 7 Bootlooping after battery drain - known bad home button

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  • #31
    Huzzah. Mine is fixed. It was still in the same state when I attempted to boot with audio ic removed but speaker amp intact, and with all caps on vdd_boost present. I added C12 jumper and a new audio ic----and it booted up with no lag and went to the activation screen.

    So conclusion for this one---iPhone 7 plus with slight diode mode resistance on vdd_boost that was due to audio ic flexion defect was solved with new audio ic and c12 jumper. Phone would NOT boot to activation screen with no audio ic on at all. That is in contrast to Mark Shaffer's finding that an iPhone 7 he tested WOULD boot to lockscreen with no audio ic, but on that one I believe it also had no speaker amp.

    note: I wrote this last night and intended to post. This phone did boot after new audio ic and continued to boot a few times with no problem, however it could not pass activation. It could not talk to sim and appeared to have a baseband problem. I tried pressing bbpmic and bbcpu no change. Tried restore (which it had passed previously a few times) and the phone failed with error 4013.

    so this is either A—baseband pmic or baseband cpu problem from board flexion (we know Board had flexion from c12 being pulled at audio ic) OR this could be heat transferred through board from removing audio ic. I did try to reball baseband pmic but this made no change. So back to square one.

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    • #32
      Mines miraculous recovery was not long lived, nor did I expect it to. It does leave me to think I have a problem with an intermittent connection though.

      The only heat I'm finding are coming from the cpu and the pmic which is usually normal during booting, and I'm guessing there getting really hot because their not getting a signal and are staying stuck.

      I've check every connection of every fpc to a known good board yesterday and did not notice anything out of the ordinary.

      I'm starting to bring my attention to that known trouble area.

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      • #33
        I took out the audio IC U3101. The pad C12 seems to have a constant connection when I check for voltage drop in diode mode. I've tried bending the board a little while measuring and I see no change. The voltage drop is 0.490V. Did you check if your pad had an intermittent connection? REWA shows the lag problem being caused by an intermittent connection, but I'm wondering if it can also have a stable connection with a higher resistance than normal instead.

        Good job on your repair Jessa!

        Comment


        • Sly
          Sly commented
          Editing a comment
          Just an interesting note, iTune detects it without Audio IC. But I'm still stuck at apple logo

      • #34
        Mine was low diode reading on vdd_boost---0.386v instead of 0.406v that made me go after audio ic. I did not bother to measure diode mode at C12--the pad came off with the audio ic. The only other one that i've measured (which had an intact but clearly spongy pad) had a normal diode mode reading. I don't think that normal diode mode readings on flexion fault lines really tell us anything.

        I believe that for mine, the reason that it would boot and be detected by iTunes, but not come to full display is the vdd_boost problem----just because I had a 6s that was the same with vccmain reading at 0.280 that would boot to normal display after bringing diode mode back to 0.330 on main. I also had a 6plus with no problem other than lcm 6v0 boost line partial short---it would take forever but rarely could boot to ios and be detected by itunes, however it made no display at all.

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        • #35
          Ok, that's good to know.

          Altought, it seems counter imtuative to me that the jumper would fix the problem of lower voltage drop on vdd_boost.

          If the trace going from c12 to the resistor was damaged I would expect it to increase the resistance value. That should increase the voltage measurement on vdd_boost if anything.

          But hey, it worked. Just curious did you take a measurement of vdd_boost with the audio of off by any chances?

          Thanks for sharing your experiences.

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          • #36
            I've ended up changing the board for my customer for this. There's only so much time I could put on it. It's now part of my side projects bin/spare parts. I'll update the post I if find the solution for it.

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            • #37
              vdd_boost is unrelated to audio ic data lines, no manipulation of C12 or its audio data line will have any impact on vdd_boost measurements up or down--they are totally unrelated. The missing pad at C12 only tells us "this board experienced flexion along this area of the audio ic" that's all. We know that some iPhone 7 get sudden death vdd_boost full short due to a bad cap, but we don't know 'why' it goes bad. Presumably due to drop, but it may be due to some kind of flexion event allowing a transient problem elsewhere that then blows the cap--we don't know.

              Vdd_boost doesnt go very many places, but asides from the caps which I had already ruled out, one place it does go is under audio ic. This is why I removed audio ic, not because of any c12 problem. Removing audio ic solved the vdd_boost partial short---the short was within audio ic, presumably due to whatever flexion event it experienced that happened to damage the unrelated c12 pad. I did measure vdd_boost with audio ic off and it was greater than 0.386 that it had been, but less than the 0.400 on my known good board. When I replaced audio ic the diode mode on both good and bad boards were the same.

              It is entirely possible that the vdd_boost value of 0.386 is within the range of normal, and that this board could not come to full display because of the damaged data line at c12. This is less likely than the vdd_boost idea because we know that boards with c12 damage boot with lag and greyed out voice memos. There is certainly the chance that there is some third explanation--something related to partial function of bb_pmic or bb_cpu, or something else entirely--we don't know!

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              • #38
                I would like to know what the vdd_boost value is on your board.

                Comment


                • Sly
                  Sly commented
                  Editing a comment
                  I'll report later today.

              • #39
                Thank you for your feedback Jessa,

                I realize that VDD_Boost is unrelated to the data line of the pad c12. That's why I was mystified by your reading of vdd_boost getting adjusted after doing the jumper.

                I see what your saying now.
                The break in the pad c12 is a symptom of the board have gone through some sort of physical damage. This physical damage might of also have caused internal damage in U3101. Which possibly shorted vdd_boost to an other line, not necessarily ground. Which might be why vdd_boost diode mode reading was lower while the chip was on the board.

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                • #40
                  My VDD_Boost reading is currently 0.410V.

                  That being said. This might of have been a different reading originally when the board first came in.
                  I recall having a lower reading of vdd_boost before starting the repair. Maybe 0.380V which I thought was a normal reading at the time. But it was not noted and I'm not 100% sure of that.

                  U3101 was removed, while thinning the pads, C12 did lift. I've installed an other audio IC, but the only one I had was from a dead iphone 7 I bought from a supplier for cheap with a really bent frame ( I don't have those IC in stock atm)

                  This was my first time working on the iphone 7 logic board, and it took longer than I expected to remove the IC which made me remove it a bit awkwardly resulting in R1103, and R3202 getting soldered together without me noticing it. This is now fixed, but voltage had been placed to the board with those two connected.

                  I think this error on my part created too many variables for any of my readings to be really meaningful. The phone still bootloops, I might of have corrupted a data line with R1103, and R3202, and the IC I've installed might be defective due the phone it came from, and being new at this board I might of have used too much heat.

                  I'll be ordering new IC soon and I will try replacing it again. I will update the post should I find the solution to this board, but I fear that I've introduced too many variables, and it will more than likely become a board for spare parts when I'm stuck.


                  I've since given the customer a working logic board in exchange for theirs.

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                  • #41
                    Stick with it--the fact that c12 came off is very consistent with this problem. I've since heard about a few other cases of this same issue and it was solved by audio ic, with one report of a bad/loose pad under audio ic that was....drum roll....vdd_boost. On yours, if it is boot looping and no longer is detected by iTunes, then this may now be a sign of baseband problems. The last two phones I opened yesterday were both shorts on bb, and both internal to bb_cpu. I am very intrigued by the mechanism of the bb faults in iPhone 7/7+---on the one I was working on for this problem it did NOT have a bb fault initially, but seems to have one now. The next thing to rule out is if heat for audio ic work is bothering baseband, since the iPhone 7 board does suck up a lot of heat.

                    Also--be aware of the Apple recall for searching no service. If your fault is actually a bona fide bb fault, then in the spirit of that program it may be covered. Might be worth looking into.

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                    • #42
                      Thanks for your ongoing support with this board. I appreciate your insight.
                      I recall the board still being detected by itune when I was done with my work. So I don't think I've over heated the BB_CPU; there might still be a chance. I will work on it again once we're caught up with our other jobs....For science!
                      --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                      On an other note, how are you guys making out with the graphical dc power supply?
                      I've been calling measurement device suppliers everyday for the past 3-4 days an no one has any.
                      The closest thing I'm starting to look into is a current data loger than I could connect to my power supply, but I did not find one with the specs that would be required for these measurements yet.

                      Comment


                      • Jessa_the_Professa
                        Jessa_the_Professa commented
                        Editing a comment
                        I can't recommend any of the DCPS graphing ones that I've tried, however the PowerZ dongle solution is pretty nice. We will stock them at iPad Rehab Supply after Chinese New Year and create some support for how to get software and set up with power squid and cables to use it to capture dcps current consumption graphs for any device. I'm not sure how useful this idea will turn out to be, but I love the potential of using this method to distinguish difficult data line faults in no power phones.

                    • #43
                      Which FB group??

                      Comment


                      • Sly
                        Sly commented
                        Editing a comment
                        What are you referring to editgitcom?

                      • Jessa_the_Professa
                        Jessa_the_Professa commented
                        Editing a comment
                        I have always maintained a private Alumni FB group for after course support for students that have come to Practical Board Repair School---I think Jerry is asking about a video that Mohammed posted exclusively there. He and Joe Ham are both alumni of PBRS.

                    • #44
                      Well, it has the potential of becoming an extremely practical tool. The nice thing about it too is that it is not exclusive to iPhone boards. We can easily carry that strategy to other devices in the future.

                      We will be bring it to our shop asap. One more tool in the box.

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