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iPhone XR boots into DFU

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  • iPhone XR boots into DFU

    Hi all! Long time no see

    I got a new case which i would like to get some help with.
    This customer has a iPhone XR which was dropped and the backcover was totally scattered. The phone is working fine and he wants a new backcover.
    We start the repair and when the backcover was replaced it was time to test.

    - To our suprise the phone didn't boot with power button.
    - When connected to charger the AM meter is giving 0.02A - 0.05A and jumps to 0.39A.
    - Connected to iTunes and it is immediately giving the pop-up message: Phone is recovery mode detected

    - I start measuring around the NAND, diode mode is fine but the power supply voltage is weird. PP3V0_NAND is only 2.6V!

    I gave the backcover a closer look and it is a little bit bend. This means the logicboard needs to flex with the backcover. I'm thinking when we screwed the logicboard (which is a tiny bit bend)
    in a straight backcover the fault occured? But this is just a theory. I cannot detect any repair pry damage.

    - I've removed the NAND because i thought: the NAND is creating the voltage drop since its a big chip and the logicboard is ever so slightly bend.
    - Measured PP3V0_NAND again without a NAND and the voltage is still 2.6V. I do not know if this is a normal measurement without a NAND but worth telling.

    What to do next, what could i do different in the future?
    Please bro, help

  • #2
    I'll have to measure the NAND voltage to be sure that 2.6v is not normal. When I get a XR in front of me I will do that for you. In the meantime you can see if there is any partial short with ohms mode (more precise for small variations in resistance than diode mode), and you could try to inject 3v0 to see if the problem is the same.

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    • #3
      I'm waiting for my iPhone XR reball stencil. Then i will measure ohms and try to inject 3V. I will get back to you to.

      Could you also check my post in: tools of the trade.
      Thanks

      Comment


      • #4
        Update:
        - got my stencil to reball NAND and i did
        - iPhone Xr still boots into DFU
        - 3utools can perform a succesfull restore
        - After restore phone boots instantly into DFU again
        - PP3V0_NAND is still only 2.681V (when in DFU)
        - Diode mode PP3V0_NAND is 0.380


        - Injecting 3V into PP3V0_NAND is not solving the problem. DCPS (thats providing the PP3V0_NAND) is consuming between 0.01A - 0.03A.


        What to do next? Should i look at U2700/PMU?
        GuruFix
        Forum Subscriber
        Last edited by GuruFix; 12-15-2021, 10:09 AM.

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        • #5
          What is the voltage on FORCE_DFU?

          Check NAND area resistors to make sure none are loose.

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          • #6
            NAND area resistors are all intact and present.
            HYDRA_TO_AP_FORCE_DFU is 1V when in DFU

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            • #7
              force_dfu is supposed to be 0v in a normal phone. Something is making this line active, either a hardware problem like an electrical bridge, or a software problem, like the CPU or power button.
              See if you can figure it out, starting with eliminating the power button and then looking for any sign of physical damage.

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