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Trolled by another no image on an iphone 7

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  • Trolled by another no image on an iphone 7

    iphone 7. This is one of my known good parts for testing boards.
    I decided to use it as a guinea pig for confirming my skills doing chestnuts.
    I desoldered it's chestnut and whilst I was doing this I smelt burning and noticed smoke coming from halfway up the board(yes coming from halfway up, not near chestnut). I thought WTF and stopped immediately. I decided to resolder chestnut. No display. I desoldered chestnut and verified it on my iphone 5s chestnut testing board. Booting with image - no worries. Try again on iphone 7 =- no go. All voltages are missing except for pin 7 - 1.8v.
    I checked for one of the 5.7v voltages on a cap further back(just in case it was a connector issue) no voltages. Given the smoking issue I desoldered all the shields to check for any signs of burnt on the board but found nothing. I cross checked seated resistance on chestnut's nut same as known good - 0.732 LHS OL RHS . And a couple more caps nearby - fine. The phone continues to boot and is recognised by the computer/3U tools but there is no image. I'm trolled.

  • #2
    Were you soldering on a board—-that was under power?
    If no, then don’t worry about smoke or burning. That’s not possible.

    We’ve learned that as expected you need practice with iPhone 7 microsoldering technical proficiency. IPhone 7 has a lot of ground and requires a lot more heat than earlier boards. You need to learn how to work on iPhone 7 by practicing. My only advice is to get a strip of chestnuts so that you are not using the same one again and again. Don’t mess with anything else, don’t change the connector or introduce other variables. Get a chestnut fully soldered back on this board. This is a great project!

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    • #3
      TechAu ebay

      Went through a few chestnuts..

      Took a fresh one off the strip each time like you advised.

      My last one I got on to the board perfectly(no reseat).

      No image. All voltages were present except 5.1v on pin 11 so I did a reflow that did the trick - booted with full image and touch. Yes iphone 7s DO require a lot more heat and dealing with that requires practice. Thanks Jessa.

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      • #4
        That’s awesome! Great job sticking with it

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        • #5
          An update

          Display now working BUT home button and fingerprint function NOT working.
          (no error message on startup about Touch ID not working)
          PP1V8_TOUCH_CONN voltage remains missing off pin 9
          Missing C3805 part of MAMBA_TO_LCM_MDRIVE
          Missing C4507 part of LCM_TO_MAMBA_MSYNC_CONN
          replaced both ... no difference.

          Next day
          Display stopped working.
          ALL chestnut voltages missing

          Undid all my work
          Desoldered chestnut - chestnut removed.
          Removed C3805 and C4507 (they were both 56pF - when I tested them with my multimeter - they're values tested ok - they were fine!)
          Pin 9 PP1V8_TOUCH_CONN now present.

          I'm not sure what I should be troubleshooting

          Attached Files

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          • #6
            No fingerrprint home button is not one that I've ever found a board problem for, always just damage to the flex either the screen or home button button flex. If you don't have anything open or short at the home button connector, then there's not much to go on when the common fault is "parts"

            If the phone does not have image, troubleshoot that.

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            • #7
              1. Normally when the fingerprint is not working AND it's a parts problem when the iphone boots to the home screen an error message is displayed. "Touch ID Unable to activate Touch ID on this phone".
              2. When the phone WAS displaying image with touch, but no fingerprint or home button function, this message was NOT displayed.
              3. After I desoldered chestnut the PP1V8_TOUCH_CONN voltage which was previously not there - appeared.
              I thought there might be a relationship and that it might signal a clue as to why my new chestnut eventually failed.

              But this was my known good parts for testing board which I used as a guinea pig for verifying a simple chestnut remove - reball - replace. I did the same on my iphone 6s known good yesterday - no problems. I'm not sure why this iphone 7 known good board is being so problematic.

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              • #8
                It is problematic because it is really really really overworked. It has been on fire and had so many cycles of heating/cooling. You can have a flex problem that doesn't produce the message, although a big tear will always produce the message. PP1v8_touch has no relationship to chestnut--why was it not there? Measurement error, or screen timed out and wasn't active....??

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