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iPhone 5s, Red Screen of Death/Bootloop & the Front Camera Data Lines

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  • iPhone 5s, Red Screen of Death/Bootloop & the Front Camera Data Lines

    Hi,
    Here is something I've found out while doing a data recovery on a water damage iPhone 5s.

    Problem:
    The phone had water damage, after cleaning the board, and making sure that the main power lines were not shortage, I booted the phone. The phone was bootlooping with the red screen.
    Click image for larger version  Name:	Redscreen 1.jpg Views:	1 Size:	47.8 KB ID:	306

    In short:
    R42,connected to Pin 7 of J1 , and R41 connected to Pin 3 of J1 (Data lines AP_BI_FCAM_I2C_SDA, AP_TO_FCAM_I2C_SCL) had there solder connection to one side of the board corroded away; which caused those data lines to have higher than normal voltage. After reconnecting them to the board, the phone booted normally and I could recover the customer's data.
    Click image for larger version  Name:	Redscreen.png Views:	1 Size:	158.4 KB ID:	307

    Conclusion:
    Red Screen on the iPhone 5s (at least) can not only be caused by a corrupted NAND chip, it can also be caused by bad data lines for the front camera.

    More in Dept:
    The phone was boot looping with a flashing red screen. I had seen online that this could often be related to the NAND being corrupted (Which I can't fix yet), but I decided to troubleshoot the board anyways just in case.

    Here is what I have found:
    Comparing Diode voltage drops to a known good board, I've seen that I had a higher volt drop on the following pins of FPC J1.
    Pin 3 AP_TO_FCAM_I2C_SCL
    Pin 7 AP_BI_FCAM_I2C_SDA

    When I followed these lines I saw that they were connected to a few resistors (R42 and R41) in parallel connected on a PP1v8 line, but the two resistors, connected to Pin 3 and Pin 7, had a higher voltage drop than the rest of the resistors of that line.

    I've realized that the water had corroded the solder connection on one end of those two resistors (this could not be seen from a visual inspection), which caused one end to be disconnected from the circuit but the other end was still connected. That was why I had a higher voltage drop to ground.

    After reflowing the resistors, the phone did not have the red screen, and booted normally! Success!

    Click image for larger version  Name:	iPhone 5s after red screen.png Views:	1 Size:	180.9 KB ID:	308
    Last edited by Sly; 12-02-2017, 06:29 PM.

  • #2
    You had red screen with fcam assembly disconnected? RSOD common fault on 5s is bad prox sensor, I’ve never seen it be bad NAND on a 5s, although if you boot with RSOD enough times it becomes BSOD which is data corruption.

    Comment


    • Sly
      Sly commented
      Editing a comment
      Yes, that was with the fcam disconnected. The issue was with partial connection with R41, and R42 due to corrosion on the pads.
      Last edited by Sly; Yesterday, 01:52 PM.

  • #3
    Iv had 2-3 rsod before without prox connected over the space of a year and a half according to my logs. None of them I ever figured out what was up with them. I appeared to have a shorted front camera line with all caps removed, the other two where unknown so I'm guessing it's possible they may be what you came across.

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