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5s - Short circuit PP1V8_SDRAM

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  • 5s - Short circuit PP1V8_SDRAM


    My iPhone 5s doesn’t boot anymore.

    I only had 0,8V at the battery connector when the battery was removed and the lightning connector plugged in.

    So I removed the Tristar but it didn’t change anything: nothing happens and instead of booting it gets very hot around L16 (near PMIC) and around Audio IC U21.

    I noticed that PP1V8_SDRAM is connected to ground (but VCC main seems ok).

    There are a lot of capacitors that can be responsible of this short on PP1V8_SDRAM.

    I also noticed that audio IC U21 had a strange aspect : as it has been getting hot on its right side (look at the 2 photos).

    There are also these 3 capacitors on its right which seems to be ok but made with a black color, and the 4th capacitor on the top right corner which is half black and half brown (!). But it doesn’t look like a burned color...

    Have you already seen this kind of short?

    Thanks for your advices.

  • #2
    IF you are sure that PP_1V8_SDRAM has a short to ground apply 1.8V on that line and try to see what is a hot spot by using one of these:
    1- Thermal Camera
    2- Freeze Spray
    3- Rosin Flux


    • #3
      And try alcohol sprayed lightly and find one shorted component that boils off dry first.



      • #4
        Let's start at the beginning. You have an iPhone 5s that does not boot. How did it get to be like that? When was it last working? What happened to it? This will guide our thinking substantially!

        Next--I am not a huge fan of the 'measure the voltage at the battery connector' strategy---that is not a native state of the device and I'm not convinced that it tells us very much to ask tristar to detect usb and output a signal to the PMIC and have that signal then open the mosfet and send usb to the battery---there are too many failure points on that path. This is not a test that I use. I have never suggested that anyone use this method, so I'm not sure where this is coming from out in the wild, I'd like to know who is advocating for this method. Similarly, we don't want to ask a phone that has no tristar on it to try to boot either.

        So with a dead phone, our first step is DC power supply. A DC power supply power consumption pattern will tell us a lot--we can see a normal boot sequence, or a short after the pmic, a short on main before the pmic, a brain dead phone, an crystal or reset problem, a boot loop---lots of different patterns. Which one did you have? We don't know and that's unfortunate. Before changing tristar, I'd like to know what the result is from the tristar tester---if we knew that tristar was indeed bad because we saw a FAIL, then that would help us here as well. That ship has also sailed---I'm pointing this out just because our goal is to learn as much as we can from any one phone, even if it is with 20/20 hindsight.

        Next--physical presentation. The only thing remarkable about the physical presentation of this phone is if the black coating has come off of the top of the audio ic between your two pictures. (it is hard to see if that is the case or if the light is just reflecting off the chip and making it appear shiny) If the coating has come off, that means you've used an ethanol containing chemical treatment (or similar) and we don't want to do that. In general, outside of light brushing with isopropyl alcohol or 3-4 minutes in a sweep frequency ultrasonic bath, all other chemical treatments are bad for diagnosis and bad for the phone, and do no good.

        The physical markings that you are concerned about are normal "splashup" of the underfill that is under the audio ic.

        Next--electrical presentation. IF you actually have a short on 1v8SDRAM that would be an unusual fault in an iPhone 5s, and certainly not a native fault. So we have a few possibilities--ONE: this is misdiagnosis. Check a few different spots to see if you have a bona fide short on 1v8SDRAM. A common way to get misdiagnosis is when multimeter probes are actually touching ground (a bracket or edge of something) when we are measuring. See if you can find a good spot to test 1v8sdram with no chance of touching any ground.

        TWO: We caused a 1v8SDRAM short by bridging balls under a chip during the tristar removal. I would remove the shield on the opposite side of tristar to see if there are any signs of heat at the baseband CPU there. I would look to see where 1v8SDRAM goes and see if there are any likely candidates that are chips. IF the device did not have a 1v8SDRAM short to begin with (DC power supply would have pointed us toward finding it if it was there at the beginning) and it does now, then there is no chance that this is a bad cap because there is no mechanism for a sudden death of a cap sitting on your bench for a while.

        THREE: IF there is a bona fide 1v8SDRAM short AND the short was present all along, then in theory you could pursue short detection on that line. I think this is VERY UNLIKELY because I've never seen a 5s get a short on that line as a native failure.

        Double check on your 1v8SDRAM short.


        • #5
          Thanks for your kind advices.
          I read everything, tested everything you explained.
          And it was actually a short circuit in PP1V8_SDRAM.
          With the freeze spray I found the guilty component : it was the C443.
          I removed it and the short disappeared ! Now when I try to boot, the apple displays.
          I'm so happy
          Then nothing happens cause I haven't put a new tristar yet, but I juste need to find a european supplier now (I live in France) and I think it will be ok.


          • #6
            I’m trying to complete this repair.
            With a new Tristar the phone is booting (that’s great!), but it takes a very very long time to reach the home page (around 2 or 3 minutes!).

            And then nothing happens: it is impossible to enter the passcode because the touchscreen does not respond. Even with a new touchscreen.

            Moreover iTunes does not detect the phone, and the battery level is stuck on 1%, even if the battery has been fully charged with another iPhone 5s.
            I have checked the charge current with a multimeter: there’s no charge current : 1 mA (if it was charging there would be around 1A).

            I’ve tried to remove Tristar again and to resolder it, but no change.
            (It’s a 1610a3, I’ve read that it is compatible with iPhone 5s)

            If someome has any advice it would be nice.

            Thanks a lot!
            Last edited by JoeBouvier; 12-30-2018, 02:37 PM.


            • #7
              The 1% reporting is a diagnostic keyword. You have a problem with the battery data line BATT_SWI. The common spots on a 5s for this to fail are pry damage at FL11. Other failure points are bad battery, or bad connection of battery, or damage to pmic.


              • #8
                I checked FL11, it has a very low resistance (less than 1 ohm) so I think it’s ok for a filter, isn’t it ?

                But while looking at it, I noticed that C25 is missing. Can it explain this iPhone slowly booting, not charging, not connecting to iTunes? On the schematic there is C25 and C23 (which is ok) between the same line (PP Bat VCC) and the ground, so I don’t think it can be the explanation?


                • Jessa_the_Professa
                  Jessa_the_Professa commented
                  Editing a comment
                  Show us the top of the board. Measuring FL11 by itself is okay, but it is better to make sure that FL11 is soldered to the board. Measure from inside the connector to the outside edge of FL11 and make sure that a gentle poke doesn't move FL11. ESPECIALLY if you have other missing "little peckers" near battery, it is very likely that FL11 is not soldered on its pads.

                  C25 missing is not important.

                  Are you SURE that you are using KNOWN GOOD parts, and not just the battery and screen that came with the phone? You have a lot of problems that are unrelated to each other, however damaged screen, wet battery etc---would make these symptoms fit together.

              • #9
                You were right ! FL11 was ok but C279 was half disconnected.
                But it’s really difficult to connect this tiny capacitor again! I have to look at some videos to learn how to do it.


                • #10
                  Only FL11 matters. You have a BATT_SWI line problem and FL11 is a common failure point. Your goal is just to determine where along BATT_SWI you have damage. Don’t get side tracked by missing caps.

                  Are you SURE that FL11 has continuity from the connector through it? If yes—move on.

                  If yes, then the next most common BATT_SWI fault is in the battery itself.

                  send us a picture of the battery connector area


                  • #11
                    I made a bridge when I was trying to replace FL11, and I decided to keep it and to test my iPhone like this.
                    It doesn’t change anything : my iPhone is still stuck on 1%.

                    And now I’m sure that the Batt_swi line is ok from the battery to the 2 pads of FL11 : I’ve tested it with a multimeter.

                    I’ve also tested the motherboard with 3 batteries and 3 screens.

                    I was reading your advices again and you say that another reason for this 1% battery can be the PMIC.

                    My first problem on this iPhone was the short on C443. Is it possible that it would have damaged the PMIC? It could be a logical explanation of what happens now with the battery gauge ?
                    On the schematic it is written « 0.454A max » for PP1V8_SDRAM, but with a short on C443 I think there has been much more current.

                    Last edited by JoeBouvier; 02-06-2019, 11:43 PM.


                    • Jessa_the_Professa
                      Jessa_the_Professa commented
                      Editing a comment
                      What is the voltage you get on fl11? And does 3utools recognize the battery data?

                  • #12
                    There is 2,02 V between the ground and the 2 pads of FL11, with my battery which is around 100%.
                    Same value when the phone is off, when it is booting and when it is waiting for the passcode.

                    For 3uTools, it’s impossible because my phone doesn’t connect to the computer.
                    The cable and the dock connector are ok, I tested them with another motherboard.

                    I’ve read somewhere that sometimes on iPhone 5s the Tristar 1610a3 doesn’t work, and it’s necessary to use a 1610a1. Do you think it might be the reason?



                    • #13
                      5s can use any 1610 version tristar, we sell the one tristar 610A3B that we use for all tristar jobs:!/%E2%8...egory=33031512

                      It is possible that you have a damaged PMIC, but I would get usb detection working first which is pretty much tristar+dock+cpu. It sounds like you reballed tristar once on this job---reballing is a skill that creates variables---are you experienced with reballing? Did it go perfectly with no oxidized pads? I would change tristar to a brand new chip, I'd use 610A3b chip and be sure that the chip orientation is correct.


                      • #14
                        I’ve tried 2 new 1610a3 Tristars.
                        All the pads on the PCB were ok, they were perfectly round and gray.
                        « Reball » is when you use an old IC? I used new tristars, and the problem of the 1% battery was the same with the 2 new Tristars.

                        I send you some photos.
                        Last edited by JoeBouvier; 02-10-2019, 10:29 AM.


                        • #15
                          That work is not acceptable. This is typical of what I call “dog damage”. Laptops motherboards can be treated like dogs, but IPhone logic boards must be treated like cats.

                          ”dog damage” comes primarily from using the wrong tweezers on the board. You need a set of extra fine bga tweezers that allow you to carefully place the chip like delicate ultra thin chopsticks—barely touching the chip itself. *any* damage to the die of the chip is unacceptable.

                          The visual quality appearance of this chip on a scale of 1-10 is about a 2. You need it to be a 10.

                          The amount of flux on this board is very excessive—the sticky flux is messy and prevents you from being able to even evaluate—is this chip 100% perfectly centered and balanced on all balls in every direction when the chip is viewed from different angles? We can’t tell. Are all small resistors and caps nearby perfectly on their pads with no damage to the ends? We can’t tell.

                          What about the pads themselves? You said the pads were gray. Gray is bad. Gray is oxidized. Flat gray pads can not make joints. You must find all gray pads and make them shiny silver puffy pillows.

                          I think you have a lot of work to do here in order to bring your skill level up to the point that you can do any diagnosis.

                          my advice is this:
                          1–keep clean. Ultrasonic this board and start with a full crisp visual examination. Note any minuscule inconsistencies and problems on the board. Look at the board from many angles. Show us anything you find.

                          2–become cat like. Use very fine tweezers. Extremely gently. Be hesistant to touch the board at all, and when you do, ONLY under the microscope and think “PRECISION” at all times.

                          3–remove that tristar and throw away—it is damaged. Show us the pads under—AFTER cleaning/ultrasonic when you think the pads are ready for a new chip.

                          4–practice first. Complete at least one tristar job on another 5s that does NOT have a charging problem. Confirm that it charges normally before and after the repair. You must be confident and 10 out of 10 with technical proficiency in order to be sure that changing tristar solved your problem.

                          5–don’t give up. I see many students that start out with work like this. These problems can be solved with effort to become precise, and experience. Keep trying.