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iPad Air 2 no display

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  • iPad Air 2 no display

    Working on a water damaged iPad Air 2 that is ON, iTunes is asking for a passcode and I can restart in DFU mode if wanted, but there is no display & no backlight. Tested with the original screen, a new replacement screen from inventory, and a known working display assembly in my recycle stack.

    The water damage seems localized to lower part of the board near the connectors. Both backlight filters were corroded and burnt up, so I cleaned the pads and jumped them for now. Both diodes read 0.144 / OL directionally so they seem fine. All LCD data lines have similar diode readings but I don't have a good board to compare them to.

    After replacing the obviously damaged stuff, I ran it through the ultrasonic, dried it, and began trying to power it on again.

    PPVCCMAIN_LCD_SW = 3.9V and has continuity across the coil/filter from the connector to the capacitors.
    I thought 3.9V may be low so I replaced U4600 with U2200 from a donor iPad mini, but the voltage remains 3.9.

    PPLED_BACK_REG_A & _B are both 3.9V, with the 12 return caps all around 0.6V

    The Mesa LDO was badly damaged so I cleaned those pads up and replaced it as well. PP11v3_MESA is missing, and PP11v9_MESA is only reading 3.6V. I don't believe these are necessary for display function so I haven't done anything more with this line. I think the next thing to do though will be to remove U4770 in case there is some hidden corrosion, and then check PP11v9_MESA for shorts.

    C4021 had some serious burn damage right next to the Touch IC, so I replaced that cap and re-soldered the IC. I tried powering it up with Stinger detached but still had no display. Stinger Boost has ~19V so the line seems to have survived.

    Right now, I've hit a bit of a wall diagnostically. I have jury duty tomorrow (wheeeeee), so this one will be marinating until I return.


  • #2
    Voltage reading for backlight aren’t meaningful—it is either main voltage or full backlight there’s no in between. Make sure you have a path from inside the connector to the diode with continuity mode. Air backlight explosions can be aggressive, so sometimes the bl pad at filter goes nowhere.

    Comment


    • AaronH
      AaronH commented
      Editing a comment
      It has good continuity from the connector to the diodes.

      I'm really just going for data recovery so even with no backlight It'd be OK, as long as I can get a data connection to the computer. I'm more concerned about why it has no display whatsoever.

      Also, PP_GPU is sitting at 0.0V even while its booting/asking for passcode which is consistent with the total lack of display. I wonder if it just doesn't see the screen attached? Triple-checking the connector legs now... Maybe trying a 'retain data' flash will wake it up? Seems risky since I'm trying to recover data.

  • #3
    Have you tested that R4607 is ll good ?, is it being told to turn on, see if GPIO_LCD_PWREN_R is present.

    Comment


    • AaronH
      AaronH commented
      Editing a comment
      I did not specifically check R4607, but GPIO_LCD_PWREN_R has 1.799V going into U4600

  • #4
    Ah cool ok, that should be ok then as the resistor is zero ohm I think.

    Comment


    • #5
      I would not attempt to do any software solutions on a device that is recognized by the computer as booting normally. Is this no image or no backlight?

      Comment


      • #6
        I think it's no image as he said that the output from the LCD driver is 3.9v which seems rather low.

        Comment


        • #7
          I don’t have schematics in front of me but image power = main is not necessarily low, what does voltage properties say for image power in the Air 2?

          Comment


          • AaronH
            AaronH commented
            Editing a comment
            It is a no image problem. Couldn't care less about the backlight. I only jumped the filter pads for the sake of convenience when I do get an image to show up.

            The schematic groups the LCD power rail with several others under PPVCC_MAIN so I'm pretty confident that main voltage is fine.

        • #8
          okay, so the current problem is no image, not no backlight. Show us a picture of the connector and surrounding area. Image is pretty straightforward usually. If it is trolling you, then it is probably the connector.

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          • #9
            https://i.imgur.com/4HEEQf1.jpg

            Comment


            • #10
              you have some pin inconsistencies in the connector, ditch the ugly looking bl caps and jump any filters to rule out variables. Find out what the square dude is at the top, probably some gate and jump him if it makes sense and if he's related to image. If I was troubleshooting image i'd try to remove as many variables as possible from this picture.

              Comment


              • AaronH
                AaronH commented
                Editing a comment
                So I went through this with a fine-toothed comb and still have no image. The square dude is the Mesa LDO which is brand spankin' new on this one, and unrelated to image. I'm not about to start jumping data chokes so really its just a matter of making sure the LCD power rail is making it to the connector, which it is, so I'm going to advise my customer to work an out-of-warranty exchange on this device, and call it quits so I can make some money on something else in the queue.
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