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

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  • lots2learn
    replied
    Ah thankyou I have closure. RIP CPU and this board goes onto the donor pile.

    Leave a comment:


  • Jessa_the_Professa
    replied
    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.

    Leave a comment:


  • lots2learn
    replied
    CPU_RESET Are you referring to RESET_1V8_L? or

    AP_TO_PMU_RESET_IN

    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

    Leave a comment:


  • Jessa_the_Professa
    replied
    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

    Leave a comment:


  • lots2learn
    replied
    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
    CHECK
    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
    SEATED RESISTANCE ON MAIN POWER RAIL = 0.369
    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

    Leave a comment:


  • Jessa_the_Professa
    replied
    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.

    Leave a comment:


  • lots2learn
    replied
    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

    Leave a comment:


  • lots2learn
    replied
    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
    07/08
    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)
    26/08
    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.

    5/09
    Reassembled into housing to be retested
    6/09
    Rapid battery drain
    13/10
    Partial touch loss down the 1/3 LHS of the display
    15/10
    Booted with Apple logo to a no display
    Subsequent boots - no display at all.
    1/11/2020
    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
    25/11/2020
    Prompt to boot USB - recognised by computer
    no display voltages - reflowed chestnut
    Prompt to boot USB immediately jumps to 430mA. Stays there.

    Leave a comment:


  • lots2learn
    replied
    How I identify power rails.....if a voltage is referenced in the name it's a power rail
    eg PP6V0_LCM_BOOST, PP18V0_MESA_SW, PP1V2_SDRAM, PP1V8
    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

    Leave a comment:


  • Jessa_the_Professa
    replied
    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.

    Leave a comment:


  • 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?
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