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iPhone 7 Tristar Hell

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  • iPhone 7 Tristar Hell

    iPhone 7 comes in with no power, pulls 0.43A from USB, customer says it was working when he plugged it in the night before. Customer admits he uses cheap shitty cables, so I'm leaning towards Tristar already.

    Tested new battery/new charging dock still no change. Will not enter DFU, only ever pulls 0.43A.
    No water damage, but someone else has replaced the screen.

    I found Pin 21 (90_TRISTAR_DP1_CONN_N) had a diode reading of .088, when it should be around .750. This was enough for me to go ahead and replace Tristar, which corrected the low diode mode reading but the phone still would not power on or enter DFU mode. I started took voltage readings across the board, finding everything was correct except PP_ACC_VAR had 0 volts but no short to ground. I noticed Q2700 was a little cock-eyed on the board, possibly in conjunction with the Tristar failure. I removed Q2700 and Q2701, cleaned and re-soldered each of them back to the board. After that, the phone powered up normally, pulled good charging amperage, and operated flawlessly until the customer picked it up the next day. He wasn't interested in buying a new lightning cable, but promised he would throw out his cheap ones and use an original apple cable.

    Fast forward 2 days later, he returns with the exact same issue as day 1. USB = 0.43A, will not boot or enter DFU. First thing I went to was Q2700 & Q2701, just in case my solder job was weak. No dice, so I replaced Tristar again. The phone now boots and all functions work, but it only pulls 0.08A via USB and the battery charging indicator never shows. It will prompt to boot when plugged in.

    In my opinion, he is still using cheap crappy charging cables and burnt up another Tristar. I'm only second-guessing myself since it is now failing to recognize that it is plugged in and will not charge the battery anymore. Did I miss something the first time? It seemed pretty cut & dry.

    Update: It will show it is plugged and charge in when connected to PC. Customer says it was doing this before it died again.
    Last edited by AaronH; 01-10-2018, 09:43 PM.

  • #2
    Have you done anything with Tigris ?, as if tristar is trashed so is Tigris quite frequently. I'd at least test Tigris voltages as a starting point.


    • #3
      Sounds like Tigris, remember —tristar doesn’t charge, it only grants charging permission. Check a known good board—when is accessory voltage present? Always? Or just when you plug in an accessory like a dongle?


      • #4
        Both times once the phone was able to power on I measured 2.99v on the accessory rail (with a charger plugged in) so I believe it is supposed to be there. I don't have a good i7 board to test against so I'll be pulling Tigris from a dead one and seeing if we get some traction.


        • #5
          I'm fairly sure but I think the accessory line should read 0 volts unless you have an accesory plugged in


          • AaronH
            AaronH commented
            Editing a comment
            It's powered back up now, PP_ACC_VAR = 3.3V , TRISTAR_ACC2 = 3.3V, and TRISTAR_ACC1 = 2.8V when plugged in. All are 0v when running only on battery.

        • #6
          I pulled Tigris from a donor board, installed it and began powering on. It pulled .08 initially, then went to 0.0 while booting, but the boot process suddenly failed and the phone went back to completely dead, pulling 0.43A via USB. I replaced Tristar AGAIN and it is now powering up but still pulling 0 amps via USB. It was pulling 0.08A until I accidentally shorted TIGRIS_BUCK_LX to ground with my probe while trying to measure it. I believe that killed this Tigris chip but I have some on the way

          Based on the initial low current draw and the fact that Tristar seemed to commit suicide again, I do not believe replacing Tigris was the solution.

          This one will be on hold until new IC's arrive, but any thoughts in the meantime are appreciated.


          • #7
            I try and replace Tigris and tristar as a pair of one dies as one can kill the other if faulty so you might say replace tristar, only for Tigris to kill it again.


            • #8
              Thoughts are: 1--usb ammeter current consumption around 0.4-0.5 is what a phone does when it is in DFU mode, i.e.
              2--Tigris faults are known to kill tristar
              3--accessory voltages are not present when an accessory is not plugged in in the earlier iPhones, I would assume same is true for iPhone 7 although I've never actually checked---look at the schematic and see if you can figure out what the accessory voltage is doing for tristar, where does it go and why?


              • #9
                Alright, back on this one.

                After replacing Tristar and Tigris as a pair, the phone continued to power on as before, pulling .008A via USB. It would charge when connected to PC, very slowly. After a while, it simply shut off again and would not power up. .001 on the amp meter, no DFU, no signs of life.

                I found VDD_MAIN dead short to ground, ran the DCPS through battery terminal and found obvious heat coming from under Tigris. Removed Tigris and found the central ground pad melting between TIGRIS_BUCK_LX and VDD_MAIN. I dug carefully to try and remove the melted traces but unfortunately the damage is too severe. No matter how deep I go, it continues to glow red and boil everything around it. The SYSTEM_ALIVE trace bit the dust so there is really no point in continuing from here. This phone is officially dead and I am officially frustrated.

                I have a feeling the damage may have been there from the time the phone was dropped off with me the first time, only intermittently at first. Really can't be certain.

                It seems tangential now, but in regards to the accessory voltage, there are several accessory rails on the 7. Unless I am reading the schematic wrong, PP_ACC_VAR looks like a supply for Tristar so it seems like it needs to be present. TRISTAR_ACC1 and TRISTAR_ACC2 also both lit up when this phone was on. However, PP_ACC_BUCK_VAR was always 0.0 and had no enable signal coming from the PMIC. That is probably the one that turns on only when accessory output is needed.


                • #10
                  Argh the dreaded internal board short, really hate them !, ultimate rabbit hole.