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iphone 8 no touch

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  • iphone 8 no touch


    iph 8 test board no prior soldering attempts
    no image
    L5754 missing
    replaced from donor board- image restored
    no touch
    touch seated resistances check ok
    touch voltages
    PP1V8_TOUCH missing
    PP5V1_TOUCH_VDDH missing

    PP1V8 comes from PMIC
    PP5V1_VDDH comes from chestnut

    I'm assuming one or (unlikely both) is not outputting it's voltage
    causing the other to fail? If it's PMIC, (having CPU on the opposite side) I'm in for a hard time




  • #2
    You knocked off a filter which a lot of people do, and you soldered it back on—great!

    Now you have no touch—how did it come to be this way? You don’t have some weird problem where chestnut or the pmic both randomly stopped working. This problem is going to be related to the work you’ve done to the board.

    it’s the connector. It is minorly stretched out so that it can’t grip the 8 screen.

    don’t replace it. Just use tweezers on the outer edges to smush it a little and try again.

    iBridge can help—the iBridge in iPhone 8 will usually solve this problem and you can see that the 8 screen will have touch when connected through the iBridge but not through the screen.

    second possibility —your screen is for an iPhone 7 and you’ve mixed them up.

    Comment


    • #3
      I get what you're saying about PMIC and chestnut - where's the mechanism for failure? What's the likelihood? Improbable!
      I checked the seated resistances thru iBridge.
      I also connected up the screen through iBridge, powered on and checked for voltages
      The screen was iph 8(iph7 and iph8 look the same except that the backing plate on the earpiece/camera/proximity sensor assembly has a ridge) - no problems testing with another known good iph 8 pcb
      With the screen connected and on I checked to see if the touch voltages were present on the pcb - nothing
      I tried squeezing in the connector plastic as you suggested. see picture - no change.
      Honestly I cant see any difference in the connector to explain pins 9, 11 having an issue - though you may?
      Attached Files

      Comment


      • #4
        The common failure these had was no touch due to the connector getting stretched out—specifically the four ground pins on the ends. When a screen was tested that was imperceptibly too thick, it widened the entire connector. When a normal screen was plugged in later—no touch.

        That may not be what is going on with yours, but it is at the top of your differential diagnosis.

        Its been a long time since I’ve seen that problem (several years). The other thing that was less common but I’ve seen twice was a weird crossover with one of the home button lines that could cause no touch. Diode mode the home button connector.

        Comment


        • #5
          I diode moded the home button connector - measurements were fine

          Comment


          • #6
            I must be missing something

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