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iphone 6 plus fails to complete boot sequence

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  • iphone 6 plus fails to complete boot sequence

    Previously this phone powered up fine. Only issue was intermittent touch loss.
    (Looked like?)Flat battery only so put the phone (semi disassembled - had the Top plate that covers the display connectors off and the battery plate) onto the charger.
    Was drawing 900mA. Decided to relocate to another charger. As soon as I plugged it in the screen flashed for a split second. Current draw went quickly to 250mA. Stayed there. So I unplugged. Back to the first charger current draw is as before ie 900mA.
    Disconnect USB. Plug battery connector directly to DC power supply. 0mA before prompt to boot. Power up. Screen lights up with Apple Logo for a fraction of a second then dead, current draw climbs in increments up to 240 -270mA and stays there for 10-30 seconds. Then drops to 0mA. Disconnect from DC Power Supply. Remove the screen. Reconnect to DC Power Supply. Now climbs to 90mA for about 10s and drops to 0mA. Press the power button - repeats. Attached is a picture of semi disassembled state of phone when this happened. Took the screen off and tested on another iphone 6 plus. Phone booted fine and the screen works A OK. So, regarding the intermittent touch loss motherboard, I suspect I've got a short on a display related power rail that's killing the boot sequence… but I'm only guessing. I think the next move is to locate all the display related power rails and start looking for a short? Seated resistance mode? Hunting down shorted caps? Is this a reasonable strategy?
    Attached Files

  • #2
    Any iPhone 6 plus with intermittent touch is touch disease. Heck, any 6 plus that doesn't have any symptoms is still touch disease, it's a massive epidemic.

    You have two unrelated problems---a phone with a complaint of touch disease, which is such a glaring signature problem that there is no need for any further diagnosis---remove meson, add the M1 jumper, reball and put it back on to solve.

    The second problem is the phone has developed a CPU data line problem while in your hands. How did this happen? I don't know.
    Troubleshoot this second problem first before you worry about touch disease--they will be unrelated.

    HOW did it come to be this way?
    A-This phone has a prior microsoldering repair attempt that somehow made it susceptible to develop CPU output open/bridged line. Maybe a solder ball under backlight driver or a nudged i2c resistor. Maybe a shield soldered back on and touching something. Start with a full microscope examination.

    B--This phone was working, connected to a charger, now not working. It could be charger damage, which would affect tristar. You could change tristar to rule it out.

    In any case, your next step is rule number one. You don't have a board problem until you know you don't have a parts problem. Work with the board out of the frame by itself, with only a KNOWN GOOD (not new, a known good that has recently been proofed with another phone) charge port, and DC power, nothing else. After that, full microscope exam of the board and report your findings.

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    • #3
      Ok I connected this board to a 6 plus screen from my 'parts for testing' (parts for testing: I purchased a fully working 6 plus, used it for two weeks before disassembling and taking its screen, motherboard, charge port flex and battery as known good parts).
      When I connected to DCPS and prompted to boot behaviour was 0 - 110mA (split second) - 220mA(a good number of seconds) back to 110mA(another split second) then 0mA (dead doesn't repeat). At this stage I don't think there's any point connecting the charge port flex. I think? I have proven it's a motherboard problem. If I take off tristar can a 6 plus boot ok from DCPS without it? If, without tristar, the motherboard can boot to the homescreen I think that would be a way of eliminating a blown tristar as the cause. Right now I don't have a replacement Tristar(that I trust).

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      • #4
        PS I purchased the phone that's now failing to complete it's boot sequence from an original owner. Person on Ebay said they were selling it for their grandmother)Didn't look like it had been opened up/worked on previously when I disassembled.
        I like buying phones this way....
        If I buy them as seconds from Auction houses, technology recyclers, pawnbrokers etc
        often I find they have been opened up and worked on - missing EMI shields, bits and pieces being a classic symptom.

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        • #5
          The only way to truly rule out a tristar problem is to replace tristar. The phone will not boot without tristar. This phone is acting like it has an information problem rather than a power problem. But "how did it come to be this way?" This one is difficult to understand HOW it went from a working phone with classic touch disease to a brain dead phone.

          Look for clues under the microscope--are you sure it never had any microsoldering done before? Is there any dried flux on the board, have the shields ever been removed?

          If not, then change tristar to rule it out. You should absolutely always have a strip of new tristars that you use as a $4.00 diagnostic tool---change tristar on a sudden onset brain dead phone just to rule it out. This is like changing the oil in a car.

          You should also be using the dock to explore whether or not any phone that you work on is detected by iTunes. Gently take the dock out of the parts housing so you can use it, or buy a $5 new dock or three and keep in an envelope. Having the right tools for the job will really help you.

          After changing tristar to rule it out, and if your crisp microscope exam reveals nothing (be sure to look under the sticker shield, and consider taking off the CPU shield to check for solder balls squeezed out of backlight driver, or signs that this board was refurbished) then put the phone in recovery mode and see what happens when you try to restore.

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          • #6
            I changed Tristar now on prompt to boot from DCPS the motherboard is exhibiting different current draw behaviour. It quickly jumps from 0mA - 120mA - 100mA to 80mA where it stays goes up to 90mA and switches between 80mA-90mA then to 100mA, then drops back to 0mA. Is this significant?

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            • #7
              Connected to itunes....restored and updated the phone to IOS 12.4.5. It has now booted successfully to the setup screen. So the cause of this was a software corruption, not hardware? I will need to put the phone back into housing so it can connect to wifi to see whether it sets up but I suspect it's going to be ok,This whole problem began when I connected the phone to an unknown charger. I was so convinced that this charger was the cause of the problem I threw it away. Could this have caused the software corruption? Or what?

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              • #8
                You had software corruption, and it was likely from charger damage to tristar. This is a pretty common failure, but unusual to actually cause it yourself.

                It was on the differential diagnosis from the beginning: (see above)
                B--This phone was working, connected to a charger, now not working. It could be charger damage, which would affect tristar. You could change tristar to rule it out.

                After changing tristar to rule it out, and if your crisp microscope exam reveals nothing (be sure to look under the sticker shield, and consider taking off the CPU shield to check for solder balls squeezed out of backlight driver, or signs that this board was refurbished) then put the phone in recovery mode and see what happens when you try to restore.

                solved!

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