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iphone 6 plus dead thru USB Caught in a bootloop on DC power Supply?

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  • iphone 6 plus dead thru USB Caught in a bootloop on DC power Supply?

    iphone 6 plus
    As per the ebay auction phone was won on
    "Phone doesn’t turn on or show any signs of life when connected to iTunes. It was working fine and the battery went flat but even after charging it didn’t turn on"
    ???????
    My test
    Phone as is doesn't prompt to boot when pressing power button
    Connected to a known good charger via USB 0mA current draw/connecting to charger doesn't prompt to boot.
    Opened up the phone and confirmed flat battery.
    Tested that the battery takes amps. Connected to DC power supply(2A @6.0volts)
    The battery took the full 2A. I charged the battery to about 3.6v and reconnected. Still the phone doesn't power up on prompt to boot. tested the phone with a different charging port connected to USB. No difference- no charging - nothing.
    Disconnected battery - connected phone directly to D.C power supply.
    0mA current draw before prompt to boot. Pressing the power button/prompt to boot.......
    The phone starts ...... apple logo...curent draw up to a maximum of 660mA then shuts down and repeats...back to Apple logo......current draws varying levels up to 660mA shuts down and repeats the whole process....stuck in a bootloop cycle.
    Where to from here?

  • #2
    Ok. I originally charged the battery some days ago and tested. I just tested the phone on DC power supply today.
    But when I retested the battery today I noticed it was completely flat so ...... I recharged it upto 3.5v.(via DC power supply) And connected. No power up from the battery. I connected up a fresh battery which was at 3.7v and retested -no power up either. Then I reconnected to DC power supply just now and......- no power up either..no bootlooping nothing! Don't know why it bootlooped maybe something that was open temporaily became (partially) connected?
    With 0mA current draw before prompt to boot I conclude there is NO short (not at least on VCC_main) so I'm not looking for a short I'm looking for an open. I'm really tempted to say this is a failure of PMIC. Maybe I should be injecting voltage into the main power rail and testing for outputs from PMIC? Where to from now? Any advice greatly appreciated.

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    • #3
      What does the crisp physical exam look like under the microscope? This is a huge part of step one.

      How did it come to be this way? You have a phone that boot loops on dc power supply. That's an information problem--more likely to be ones and zeros somewhere than any kind of power problem. Candidate problems---bad tristar from charger damage, failed NAND, flexion damage between CPU and NAND or software corruption.

      Side question--why did it boot loop initially on dc power and now it doesn't? Answer--because it isn't connected correctly, or it isn't receiving the prompt, or you are prompting by usb without taking out the usb which will then mask a phone autobooting to recovery mode at 70mA. Troubleshoot this until the phone does the same thing every time---your original boot loop could just be poor connection at battery and you are prompting through usb---that will be the same as asking a phone to boot with no battery via usb---which will boot loop.

      Once you get the same result every time on DCPS, then proceed.

      It would be nice to put this phone on a tristar tester, but that's not really necessary. Either way the next step if the phone is boot looping is to change tristar.

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