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Vertical no touch lines after replacing Meson and Cumulus

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  • Vertical no touch lines after replacing Meson and Cumulus

    Hi. My first post here, and I've just subscribed to the forum after having watched the YouTube channel for a few years now. Firstly, thanks for all the free advice thus far! Secondly, go easy on me as I get used to any forum rules and quirks I'm not aware of yet! Apologies in advance if I mess up.

    OK so I have a customer's iPhone 6 Plus which exhibited signs of Touch Disease: touch would work intermittently. When it didn't work, it was the whole digitiser.

    I replaced the Meson IC first, as there were no white bars or blocks. When I tested the phone, it showed signs of ghost touch and touch failure, and the board was getting pretty hot. I considered that I had not replaced the Meson IC properly, but then I started poking around with the Cumulus and a part of it crumbled at the barest of touch. So I replaced it also.

    The phone no longer got hot, and there is no sign of ghost touch. However, there are dead spots along two vertical zones - one at the very left hand edge (if you try to type Q, a W is displayed), and one just a little left of centre. I've tried three different screens, all with the same result.

    So far as I'm aware, the phone has not been worked on before. Board looks clean and free of liquid intrusion. The chassis is slightly curved (of course). Touch on the screen, other than those two vertical lines, is fine.

    I no longer have access to a bench PSU, though I do have a multimeter. I am unsure what to investigate now. I don't recall ever having a problem like this that wasn't solved by replacing the screen.

    Anyone got any ideas?

    Thanks in advance,
    Paul.

  • #2
    "Crumbling with the barest touch" ---this means technician is doglike instead of catlike. I notice this when watching students learning to microsolder---some students (usually men) are just kinda rough. They poke at the board willy nilly with regular size tweezers, they get nicks and scratches all over the place and they will try to rub off silicone without using heat. Remember---MacBooks are dogs, iPhones are cats. You can get away with a lot of roughness on MacBooks--they are tough, big, and forgiving. But iPhones require "the girlfriend touch" to quote a former student from Korea.

    If you have a dead line of touch after changing meson---the problem is bad meson placement (or a bad chip if you are using reballed chips from china--new chips are clean under the microscope and cost $7/each).

    Look at the schematic and try to guess what removing any one pin of the digitizer connector would do--then follow those lines thinking about how they could fail. The only practical failure point with this history is "meson is bad or not soldered well"

    Try again!

    Comment


    • #3
      Yeah, that's what I thought. I must have squished it somehow, and squeezed a couple of solder balls together. Thanks for your reply.

      In my defence, I have to say I normally have a "girlfriend touch", and I've never crumbled an IC before (unintentionally!). To put it another way, "this never happened to me before!"

      The tweezers I'm using are CHP 7SA. I'm not learning to microsolder, as I've been doing it for years... though I'm ALWAYS learning! The ICs looked pretty decent under the scope.

      In your defence(!), I could have just screwed it up! I've had a short hiatus from fixin', I've not done that many Meson/Cumulus swaps to date.

      UPDATE: I swapped out the Meson again. I'm getting no touch in exactly the same two vertical lines. I'm considering swapping out the Cumulus again now.

      My other thought is that I've been sold crappy ICs. I will update again after I've swapped out the Cumulus.

      Comment


      • Jessa_the_Professa
        Jessa_the_Professa commented
        Editing a comment
        Look at the schematic--dead line of touch would be one of the lines that go from connector to meson, or one of the lines from meson to cumulus. Your problem has to be somewhere within these options. Keep trying. If several chip replacements don't solve, and you're sure that the connector is pristine and your test screen is good, then explore whether or not you have a pad problem under meson by taking diode mode readings at the pads under meson.
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