Welcome to the NEW iPad Rehab Forum! Everyone is welcome to read posts and learn for free. If you'd like to post your own question on the forum, please click "register" above or go here: to enroll as a paid subscriber for $29/mo for unlimited access to our forum support and private signature failure section.
See more
See less

Iphone 6 plus USB boot jumps straight to 430mA after chestnut reflow

  • Filter
  • Time
  • Show
Clear All
new posts

  • Iphone 6 plus USB boot jumps straight to 430mA after chestnut reflow

    This phone has had a long history of work that I have done on it however recently it stopped displaying image. The phone did boot thru USB and was recognised by the computer so I assumed it was a display problem only and checked for display voltages coming from chestnut. In their absence decided I would reflow chestnut. Before doing the reflow I heat sank CPU by placing a coin on top. Reflow was 380 degrees at 100L air for just under 50s with a 7-8mm nozzle - Quick Hot air station. Now, after the reflow, prompt to boot through USB current draw jumps straight to 430mA and stays there. I desoldered chestnut, checked for shorts, and once again prompt to boot through USB. Same jumps IMMEDIATELY to 430mA. CPU is dangerously close to chestnut. Did I fry CPU? If so this is a post mortem. How can I avoid frying CPU in future?

  • #2
    When should I "reflow chestnut"? Answer = NEVER. Well, almost never--the only time this would be indicated is if you first replaced chestnut, and weren't quite sure if it had soldered on completely. ONLY in that case would you heat up chestnut and nudge it. Chestnut is not a chip that "comes loose" in any way, so we don't "reflow" chestnut.

    Then what was the reason I had no image to begin with?
    That is a question that can only be answered by multimeter. Start with diode mode in the connector--is there any short or open on chestnut outputs? Are we sure that chestnut was being told to turn on?

    The MOST LIKELY reason for no image in an iPhone 6 plus that is otherwise booting is LONG SCREW DAMAGE that tears a trace that enables chestnut. If you're not sure--desolder the lcd screw brackets to check for LSD.

    What about now.
    WHY does this device have 430mA current consumption after prompt to boot? Somewhere some line is short. I do not know where. YOU have to figure out WHAT LINE is short. Use your multimeter to find a line that has lower resistance to ground than in a normal iPhone 6 plus. The most likely case is some line that is near the area that was heated. This may indeed be a line that is within the CPU like 1v8SDRAM, but it could be many others was well.


    • #3
      How I identify power rails.....if a voltage is referenced in the name it's a power rail
      If a voltage ISN"T referenced in the name then it's probably a dataline
      seated resistances of power rails checked in the area CHESTNUT off
      see attachment
      I'm having difficulty identifying the shorted line - No joy here. Also, connected up to DCPS 0mA (via battery connector)before prompt to boot 40mA(0.04A) on prompt to boot, where it stays.
      Attached Files


      • #4
        I'm now posting below a log of all the work I did on this phone in hope that it may help shed light on the existing problem

        Recap on history in 2020
        Original fault - intermittent touch loss.
        I used the phone - this was the only problem. The phone booted and shutdown ok….touch came and went periodically
        Then oneday I connected to faulty? charger
        No longer booting
        5/03 replaced Tristar

        22/7 Battery level misreads
        Random shutdowns
        Removed from housing connected with known good charge flex, battery and screen.
        Random shutdowns continue
        24/08 ???? (this part doesn't make sense)
        charges with macfixit battery ok!?!?
        no shutdowns THIS PART IS QUESTIONABLE
        no touch(original fault)
        Attempted Touch IC repair (M1 jumper)
        faded screen - no touch - then "came good"
        faded screen gone, had touch
        shutdown and on restart the problem reappeared
        Tested good with two white screens= assumed it was a screen/connector issue.

        Reassembled into housing to be retested
        Rapid battery drain
        Partial touch loss down the 1/3 LHS of the display
        Booted with Apple logo to a no display
        Subsequent boots - no display at all.
        Prompt to boot USB
        increments up to 320mA, drops back to 260/200mA. Stays there - not recognised by 3U tools
        Prompt to boot DCPS increments up to 610mA
        Prompt to boot USB - recognised by computer
        no display voltages - reflowed chestnut
        Prompt to boot USB immediately jumps to 430mA. Stays there.


        • #5
          Note chestnut is currently desoldered off the board.

          What short on which power rail could cause immediate jump to 430mA on PTB thru USB

          Note PTB thru DCPS current jumps to 40mA(0.04A) and stays there

          THOUGHTS - making sense of my own history logs(trying to). inconsistent results and some "trolls"
          Two separate non related issues
          (1) Loss of image/partial touch loss - possibly connector issue "trolls" Connector image issues usually vertical lines/faded screen
          (2) Charger damage that was not fully addressed by changing Tristar(maybe Tristar replacement was not good - maybe there was something else wrong that damaged the Tristar replacement) . Subsequent symptoms(intermittent?) - battery level misreads, random shutdowns & battery drain but never directly addressed - they just SEEMED to disappear.

          NEWLY exhibited problem. Is it a NEW problem or an exacerbation of an existing one see point 2


          • #6
            Here is some general advice.
            History suggests that when you microsolder to fix problem A, you create problem B. You need experience. Gain that experience by Doing procedures on working boards. First confirm that you can change chips XYZ reliably on a WORKING board. THEN do the procedure on a board you’re trying to troubleshoot.

            If you want to fix this board the problem will be from work that you did. Step one: erase all the prior repair. Remove chestnut and meson. Check for solder balls popping out of underfilled chips.

            see what the the phone does on dc power.


            • #7
              Chestnut desoldered

              DCPS 0mA B4 PTB

              DCPS 40mA PTB
              1. goes straight to 40mA
              2. Stays there
              1. Desoldered Meson - no change
              Desoldered/replaced Tristar - no change✘
              What to to next?
              27-Aug-21 4:35 PM
              is the phone getting the signal to turn on? BUTTON_TO_AP_HOLD_KEY
              1. on key press = 1.8V - 0V
              1. the main power rail present? 3.684 3.64v
              is PMIC making subrail voltages?
              NO (I checked three)

              I'm not sure how to prove where the problem is?
              Chestnut on the iPhone 6 plus is(dangerously?) close to CPU.

              Attached Files


              • #8
                Do you have a solder ball sticking out of Mesa boost ic?
                what are the pmu outputs you measured?
                check the voltage on CPU_RESET


                • #9
                  CPU_RESET Are you referring to RESET_1V8_L? or


                  RESET_1V8_L on power on goes from 0v to 0.04v

                  MESA_BOOST I took it off to be sure - no squeezed solder balls


                  • #10
                    There’s your answer.
                    CPU Reset line should be 1.8v You have electrocuted the CPU when you “reflowed chestnut” by bridging one of the high voltage chestnut lines into RESET_1v8_L under chestnut.


                    • #11
                      Ah thankyou I have closure. RIP CPU and this board goes onto the donor pile.