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iPhone 7+ with 0.98a Short

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  • iPhone 7+ with 0.98a Short

    I have a 7 plus that according to the customer stopped working in his pocket, he knows this because he felt the phone get hot and realized it was off. I asked if it had had liquid or drop damage and he said it just got hot and was off when he checked.
    I thought could be short (heat) and hooked up to dc where it pulls 0.87-0.98a @ 3.7v. I Then isolated parts to rule them out (hooked just the board to dc) and the same happened.

    Edit ...... Phone pulls 0.98a as soon as power is connected (before being prompted)

    I thought ok must be pp_vdd_main or pp_batt_vc, this should be an easy find, of course thinking that is a bad idea as both lines have no short and seem fine in diode mode.
    I then thought where do I go from here as I have no clue? so logically followed pp_vc_batt from fpc measuring as I went and there was nothing out of ordinary, so far I am at tigress and Tristar and the only line that I have seen that seems remotely odd is when I got to pp_5v0_usb (1.404 on diode mode) I don't have a known working to test but I have seen lines this high as the norm.
    I then removed Q2101 to test for heat from dc and it seemed to be getting warm around tigress so as there are only a few caps on the pp_5v0 line I thought quickly remove these to test as that line leads to tigress.
    This wasn't the problem as line stayed high and tigress was still getting warm, so I thought maybe tigress has a fault so replaced tigress and the fault still remained and tigress still gets warm.

    As it stands I have come for advise as I think guessing is bad form and that is what I will be reverting to from this point if I continue, has anyone got any suggestions?


    Small scuffs on one corner of the housing, the phone is in generally good condition.
    Customer says the phone got Hot in his pocket and was off when he checked.


    pp_vdd_main 0.316 in diode
    pp_batt_vc 0.325 in diode
    pp_5v0_usb 1.400 in diode
    Tigress Changed

    Thanks in advance
    Last edited by Shrimply Pibbles; 04-17-2018, 08:36 PM.

  • #2
    Is it pulling 0.98A when the phone is off or when you are trying to boot?
    Did you check PP_VDD_BOOST for a short?


    • #3
      Originally posted by Shrimply Pibbles View Post

      As it stands I have come for advise as I think guessing is bad form and that is what I will be reverting to from this point if I continue, has anyone got any suggestions?

      You are already guessing! And you're right--stop doing that!

      What you know is "this board has a shorted line somewhere" Your next goal is to determine "What exact line is short?" And once you know that, figure out why. Pulling components off a board when you don't know what line is short is adding variables to the problem instead of simplifying the problem.

      So how to figure out what line is short?

      One method is to use your multimeter and probe around checking lines in diode mode as you have done. Like GuruFix above is asking you--was you 1A short BEFORE prompt to boot? If so, then the short must be before PMIC, if not, it must be after. You have unfortunately pulled off components that we would need to do that test now, so hopefully you remember. If short was BEFORE prompt to boot then check vdd_boost---look at schematic. Figure out what this line is for and how it is related to vddmain.

      If short is after pmic (before current was 0.000A before prompt and only 1A after prompt) then you can check some common faults---1v8SDRAM be at the top of my list. Other than that, probe around randomly looking for a shorted line, and then confirm in diode mode.


      • #4
        Jessa_the_Professa GuruFix Sorry i thought i had put that in the post my bad

        It is pulling power as soon as it is connected (hence me only checking out those two lines and not elsewhere) and there's me thinking i proof read durr.

        GuruFix i will check that line out now to see what hes all about and update tomorrow.

        Fyi both the caps were replaced along with new Tigress (all be it adding variables) , I know what your saying Jessa That's why i stopped there , there was some thought behind removing it as there was a what i assumed was a high line and heat from tigress. That cap is right next to tigess, so that was my thought process i removed tigress to see if the line returned to normal (if it was even high in the first place). I wanted to see if that was the issue or was it being caused by tristar or a line leading to tristar.

        I was trying to think logical as the two lines that normally cause this problem were fine, i thought by tracing the problem from the power source i mite get a clue on what line was causing the issue before asking for help.

        Any thoughts after that where guesses and i stopped and thought i know some guys who can help, i will however in future ask before removing as i know it makes diagnostics harder.


        • Jessa_the_Professa
          Jessa_the_Professa commented
          Editing a comment
          Always find what line is short before you remove any components.

          You got trolled by the mosfet---look at the schematic. There is no path to ground for the batt/vccmain mosfet. It will ALWAYS get hot on any phone with a vccmain short when voltage comes in at battery. But since it has no path to ground it can't be the cause of any short. Tigris appeared hot just because it was next to mosfet.

          Regardless---if you know you have a short, but you don't know what line is short---then don't take off anything until you figure out WHAT LINE.
          Tristar has no connection to main or battery, so it can't be part of a problem on a before prompt to boot current leak.

          Use your multimeter and find the shorted line. You already got a big hint from GuruFix!

      • #5
        Thanks for the advice Jessa_the_Professa I will certainly do this from now on. I will also have to get better at writing these posts too as I also left out removing and bridging the mosfet for testing and that is information you need eeek.


        • #6
          GuruFix That line was short on C2527 removed/replaced and all running fine Happy Days Thanks for the help GuruFix . and Jessa_the_Professa

          On a side note, PP_VDD_BOOST seems to boost a lot of sections of the board LDO Input PMIC, WI-FI, Audio IC (Codec), Mesa, Mamba and a few other connectors. Am I right in thinking this is pre-PMIC and generated solely off VDD_Main? If so are there any other lines that are like this in the 7 and 8 range? I only ask as before The 7 range It was Normally just vc_Batt and vc_Main that would be short when pulling power before prompt.


          • Jessa_the_Professa
            Jessa_the_Professa commented
            Editing a comment
            somewhere in the schematic it says that vdd_boost is the same as vccmain and used to boost vccmain when battery is very low or something like that.