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iPhone 8 Plus Partial Backlight Problem

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  • iPhone 8 Plus Partial Backlight Problem

    Hi! This is my first post, so I'm new here. I'm grateful for your time reading my post and hoping someone can help.

    iPhone 8 Plus was working as normal, prior to screen replacement. After screen was replaced there was no image.

    A visual inspect found that FL5705 had come off the board, taking one of it's pads with it. The otherside still intact, I soldered a replacement filter, and then I have created a jumper, from FL5705 to C1812, which restored image. Hooray......

    However, I now only have partial back light. I have created this jumper before, but I also tried going directly from C1812 to C5705 but I have same result. Voltage on that line measures 1.8v as expected.

    I've then started to inspect backlight circuit. All contacts on J5700 give correct diode readings, however voltage at TP0532 is 10v, and voltage at TP0535 is 3.8v. My understanding is that both of these anode line voltage readings are lower than the 18v that they should be, but I still checked the backlight circuit for TP0535 and I have continuity around the circuit. As the voltage reading was quite high (but not high enough), I suspected U5660, replaced but still the same.

    Is the power line for both of these circuits shared? Is not enough power being delivered to the backlight circuits and so should I be looking elsewhere?

    I am still learning, would appreciate any help advice or thoughts and hope I've provided enough information.

  • #2
    Does anyone have any ideas please as to what I can or should try next? Be grateful for any help or support.

    Comment


    • #3
      Hey there,
      It sounds like you're troubleshooting half dim backlight on an 8plus that had DIY pry damage near the LCD connector.
      With that history, the most likely failure point is #1--damage to the screen and #2--damage to the connector.

      You'd be surprised how even incredibly minor damage to the pin position within the plastic of the connector can make the screen fail to grip the screen and generate an open line.
      Show us a picture of the connector.

      Comment


      • Jessa_the_Professa
        Jessa_the_Professa commented
        Editing a comment
        edit: show us pictures of the connector taken under a microscope from the top down angle and from a side angle view.

    • #4
      Originally posted by Jessa_the_Professa View Post
      Hey there,
      It sounds like you're troubleshooting half dim backlight on an 8plus that had DIY pry damage near the LCD connector.
      With that history, the most likely failure point is #1--damage to the screen and #2--damage to the connector.

      You'd be surprised how even incredibly minor damage to the pin position within the plastic of the connector can make the screen fail to grip the screen and generate an open line.
      Show us a picture of the connector.
      Thank you for your reply.

      We have tried different replacement screens. The connector looks ok? I have continuity between J5700 PIN 45 and TP0535. Diode reading of PIN 45 is around 470. But voltage only 3.7v on that line. I have replaced U5660, I only have 3.7v at resistor R5733 either side.

      Any more suggestions would be appreciated.

      Comment


      • Jessa_the_Professa
        Jessa_the_Professa commented
        Editing a comment
        The connector is NOT OKAY. Look at pin 43--this is the "incredibly minor" connector damage that I'm talking about. Bend that pin out so that it is not pushed in too far into the center of the connector like it is now. Insert a tweezer and press the pin back toward the outer edge of the connector away from the middle.

        After you get backlight working, then I want you to edit that jumper. You can NOT give a phone back to a customer with that huge jumper. The gauge of the jumper wire is much too large for that line, and you don't want to run a jumper from under the CPU shield if you can help it. They need the soldered on CPU shield to have good heat transfer to cool the CPU, it can't be sitting on top of a thick jumper. Get backlight fixed and then correct that jumper. You need to keep it short, from the exposed via at FL5705 to the opposite pad. I would rather you make a very tiny jumper from the via to the pad rather than the long jumper you have now.

        We also want to correct the reason you got into this mess to begin with. Train your technicians to NOT USE plastic tools for disconnecting flexes. Always use fingernails. Then you will never knock things off the board.

        FYI--backlight voltages are always all or nothing. You will have battery voltage all along the backlight lines unless everything is working--only then will you see the boosted voltage. Right now your voltage on backlight anode 34 is low because you are open between the connector and the screen (assuming all the backlight circuitry replacement that you did is perfect.)
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