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Water damaged Iphone 6 - No Boot

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  • Water damaged Iphone 6 - No Boot

    Hi,

    After typing the message below, I felt it necessary to give a brief introduction/background as this is my first post. This is my first dive into phone repair, but I am no stranger to general electronics/electrical repair as a hobby or simply out of necessity. I am a EE, but my post-college experience is mostly around industrial electrical and instrumentation. I have (and am obtaining) most of the needed tools and equipment to do these repairs, but I am new to the nuances of the iphone platform and troubleshooting techniques.

    I am attempting to repair (recover data from) a water damaged Iphone 6. It was not submerged but received enough water (presumably through the SIM card slot) to cause damage. Unfortunately, it wasn't immediately powered off and attempts were made to reboot, hard reset, and charge during the hours/days following the water intrusion. I understand that, at one point, there was a red screen, but it also booted normally once several hours later then died within a minute (phone already had a failing battery).

    After opening the phone, the only signs of damage were around C5202. It was a copperish (green) corrosion that was then cleaned and verified that the capacitor was not shorted. That said, I have elected to wait until my new hot air station is delivered before attempting to remove the shields.

    Tests that have been done include basic short circuit tests VCC_MAIN, a number of capacitors, etc. USB power draw is ~510mA. On a DC PS, the current draw is 30mA until the power button is pressed and it increases to ~110mA. I suspect that the phone may be booting, but I have no working interface to see it (USB comms or screen). I think this because of the current draws I mentioned and because the shield above the processor gets warm (ever so slightly warm, not hot by any means).

    As this is a data recovery mission, I haven't looked at the screen or it's associated circuitry, but I may do so if I can confirm the phone's brain isn't a total loss. My current thinking is that maybe data isn't passing to the USB connector, but I am not sure what I can do to validate this. What are your thoughts.

    Matt

    EDIT: I did some additional checking under the "soft" shield where the U1202 is located. It seems that numerous capacitors are showing shorted: (C1226/10/75/90/94/45/28 and C0447/8/9 and C0435. There are also some smaller ones in a cluster near C0435 that have four pads each and I think they may show the same thing, but I'm not as familiar with that packaging to know if I tested them correctly. So, my thoughts are now that there is one thing that all of these have in common which is likely shorted and causing them all to appear shorted. I am working to see if I can figure out what that may be.

    Last edited by plutonium233; 06-08-2018, 03:22 PM.

  • #2
    Welcome to the forum--unfortunately your post is my worst fear! I ABSOLUTELY DO NOT ADVISE that anyone work on a phone with someone's important data on it until they are have a well established experience base for iPhone repair. It is very easy to make a recoverable phone become unrecoverable---this one is a great example. You are putting electricity into a phone that you know has corrosion that hasn't been cleaned, especially one that once had red screen (which is often a deal breaker and a super dangerous fault--it leads to an unrecoverable state). My strong advice is to send this phone to a competent professional and not risk anyone's data.

    Let's assume that this is your own phone and that you're not going to send it for data recovery and that you are willing to risk losing a potential path to data with your own data. If that is the case then:
    1: Do nothing until you have the shields off if there is any evidence of water on the shields or the board near the edges of the shields. Practice on a donor board first. It is not easy to take off the bottom shield on the top of the board and the one by the CPU is often overheated by folks on their first couple of tries which will kill the CPU and the phone will not be recoverable. After shields are off, then do a full microscope exam and ultrasonic cleaning. Only then apply power to the board.

    In the meantime, look up on the schematic what line C1226 and brethren are on and then tell me why this line is not short despite the fact that your multimeter beeps to ground on both sides of the caps.
    DO NOT put heat on the board near these caps or attempt to remove any of them!

    Comment


    • #3
      Jessa,

      Thanks for the reply, and I appreciate your concern. You are correct in your assumption that this is my phone, any data that is on the phone has already been counted as a loss and of little consequence. I would not attempt to recover someone else's important data on my first or even 10th attempt. My goal here is to learn more about and do something I enjoy both as a profession and hobby. In this case, I'm coming back to a portion of the field that I haven't explored much since college as my job is mostly in power/control/instrumentation engineering rather than microelectronics. Again, I am no stranger to a soldering iron by any means.

      I'll admit, I jumped the gun on some of my diagnostics, but that was on the basis that my initial visual inspection did not indicate anything more than very localized water damage in one specific area. I agree that I should have at least done an ultrasonic cleaning before anything else. My thought on using the power supply was that I was relatively safe since I had the current limited to a very low value and had already performed initial short circuit checks with my multimeter.

      I am going to move forward with shield removal once I find a board on which to practice. Do you have any recommendations on max temperature, distance, and/or duration to avoid damaging the CPU? I would assume that, as with anything else, the technique is to put the heat only where it's needed and be mindful of thermal mass and heat transfer so that I don't apply too much heat for too long? I'll take a look at some more videos in case I overlooked any good information there as well.

      I have gone back and reviewed the schematic and re-tested those capacitors. I see that my meter was beeping due to the relatively low impedance on this line (0V95). When I made those measurements before, I was relying on the feedback from the sound instead of looking at the display (yes, I know better) since I was attempting to focus on what I was doing with the probes. I also see that there are several chips and capacitors connected to this line which is the reason for the lower impedance (that, and the low voltage normally present on this rail.

      Matt

      Edited to add: When I say visual inspection above, that was with both no magnification and a microscope. The board actually looks really good, better than many I've seen in videos. All the capacitor ends and plated contact pins on connectors look shiny and clean.

      Last edited by plutonium233; 06-11-2018, 04:00 PM.

      Comment


      • #4
        Ok, fair enough. If you do not think you have evidence of water under the shields then it is not unreasonable for now to choose to leave them on. If you do take off shields try to aim the air directly down on top of the shields, with max heat and max air flow on a nozzle around 8mm--this will "sear" the shields off quickly. Practicing on some dead boards is a great idea. Grip the shield with tweezers and allow the board to drop a few cm away from the shield by gravity. The solder holding the shield on the board seems to be a lower melt alloy than the regular lead free so you can usually get the shields off without disturbing anything else.

        You have focal corrosion on this board and it is only around C5202_RF. You have a 30mA current leak before prompt to boot. Assuming that you know that with this DCPS on a normal board it is 0A before prompt to boot then you know you have a leak somewhere before the power management chip. This combined with corrosion on a known signature failure point that is on vccmain points to C5202_RF being a problem. You claimed that this line is not short----are we sure that the resistance of this line is normal and not partially short? The standard way to ask this question is to take a diode mode measurement with red probe on ground and black probe on the line. iPhone 6 vccmain should read about 0.334v diode mode reading. If is 0.289 or less this is why you have a 30mA leak--knock off with a razor blade.


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        • #5
          Thanks for the reply. I did decide to proceed with shield removal and was able to easily remove the processor shield with no issues. Under the microscope, I see no signs of movement or reflow on any components. That said, I do see some signs of hidden corrosion near the edges of a couple chips. Actually, the ones I see could have been detected without this step as they were on the side where the soft shield lives. I had to turn the board sideways and make a few adjustments to see it. Under the processor shield, there are minute signs of corrosion near a resistor and capacitor at the corner of the processor (I am away from the board now, but I think at least one of these is associated with the backlight anode). At this point, I will move forward with ultrasonic cleaning before going any further (with all shields removed now that I know water DID go further than expected).

          As you suggested I did question the 30mA leakage current as that seems very excessive even if the design included room for standby current to some component(s). However, I did not know that it would be isolated to VCC main upstream of the PMIC "black box". It does make sense though since I would assume the prompt to boot is what tells the PMIC to send voltage to all of the downstream voltage rails feeding other components.

          Regarding C5202_RF, I now know why my initial resistance measurement on this cap did not show a partial short. I had not received my microscope as of the time when I identified the corrosion on this capacitor, and it turns out that, after cleaning, the top of the pad had actually corroded away on one side so my test was invalid. For anyone else reading this, don't make any decisions without observation under a microscope! So now, I will remove this capacitor and re-test VCC main. I did not see the partial short on VCC main when I did my first diode mode check because I did not know the nominal values to expect, again my fault.

          I appreciate your help and patience with me on this!

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