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iPhone SE no backlight can't find correct schematic

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  • iPhone SE no backlight can't find correct schematic

    Hello all,

    New to the forum and in advance I'd like to thank you for your help! I'm fairly experienced in electronics and macbook motherboard repair but I'm still learning my way around iPhone boards so please bare with me.

    I have an iPhone SE. The phone looks like an iPhone 8 and originally came in with no power. The no power issue was resolved by replacing the battery and charge port. It would only work if we replaced both of those things. After this it powered on perfectly but became intermittent. It eventually gave no display at all and it turned out to be a missing back light. I'm not sure if the back light may have been the issue all along and not a no power issue as we thought originally.

    Unfortunately I cannot seem to locate the right schematic. Checking into PhoneBoard software they have an iPhone SE listed between iPhone 7 and 8 however the board I have looks much more like an iPhone 8 with some differences. I'm a little bit lost as where to go from here without the schematic. I did some diode tests around the display connector and found nothing obvious. I see no corrosion and no physical damage such as burns.

    Where can I get this schematic and what are your recommendations for diagnosing this device. Thank you!
    Last edited by computerprodigies; 09-15-2021, 08:54 PM.

  • #2
    Hey there,
    welcome to the forum. The phone you have is referred to as “2020 SE” and it is quite like iPhone 8. There is no schematic outside of Apple right now.

    2020 SE shares common problems with iPhone 8.
    Before changing a dock and battery, the tool to use to differentiate “doesn’t turn on” from “no backlight” or “no image”
    is DC power supply at battery connector.

    If you are sure the phone turns on now (iPhone 8 can get intermittent doesn’t boot that is solved temporarily with pressure at CPU) then differentiate no backlight from no image by prying the backlight from the lcd and shining a bright light from behind. The image, if there, will be clear as day.

    One of the common problems in iPhone 8 is plugging in an iPhone 7 screen which stretches the connector slightly, so that a native screen doesn’t light up. With tweezers you can “gently smush” the connector under the microscope so that it fits the screen perfectly.

    Are you sure this is no backlight? Or is this no image? Or doesn’t boot?


    • #3

      The issue is definitely no back light. I can see the Apple logo on the display panel during boot up. I see a diode next to a bank of capacitors on the rear side of the board which looks like it may be the supply for the back light. A diode mode measurement here gives me 0.557V This leads me to believe the actual circuit itself is fine. I am wondering if perhaps we may have damaged something during our previous diagnostics and blew a back light fuse or something similar. Unfortunately I am not sure where that filter is on this particular board and without the schematic I'm pretty lost.

      I checked the connector for the damage you mentioned and all appears normal.

      EDIT: After some poking around it seems like some of the pin placements on the two display connectors are the same as on the iPhone 8. At least when it comes to the location of the grounded pins. I ran a continuity check from the anode of the diode I mentioned earlier as being the possible back light boost circuit and found that this connects to pin 37 of J5700 like an iPhone 8. On the Iphone 8 this would be PP_DISPLAY_BL_ANODE_CONN. On the iPhone 8 the two neighboring pins to the left and right are the cathode connections. Measuring these cathode connections gives me 0.734V and 0.736V. If these two pins are also Cathodes on the iPhone SE 2020 then it would appear these two lines are good and there is no blown fuse or short to ground. The same can be said for the Anode line as there is continuity between connector and diode and no shorts to ground.

      I also found that in this board pin 31 measures short to ground. However looking at the trace it looks like it connects to the ground plane but am not entirely sure about this. On the iPhone 8 it looks like this connection is called MAMBA_TO_DISPLAY_MDRIVE. This connection also leads to PIN 12 of J5800 through FL5860. On my iPhone SE 2020 this pin 12 of J5800 also tests short to ground and I cannot locate a FL5860. In short I'm not sure if on the Iphone SE 2020 these two pins are revised and connected to ground or if there is an actual short here.
      Last edited by computerprodigies; 09-16-2021, 08:50 PM.


      • #4
        On boot— you see a dim Apple with no backlight? Or you see the full brightness Apple logo that then goes dark?


        • #5
          Dim apple logo. Back light doesn't show up at any point.

          EDIT: Attempted replacing the chestnut IC as well as back light driver IC LM3539 with no luck.
          Last edited by computerprodigies; 09-17-2021, 07:35 PM.


          • #6
            For correct diode mode measurement on 2020 SE you can use zxw. Phoneboard is okay, but not as good as zxw. Pin 31 is indeed ground in SE 2020
            In my experience if you have image, and correct diode mode reading on backlight anode and cat lines in any iPhone the problem is the screen or the connector pins are microscopically too wide and not actually making contact with the screen. If you are getting battery voltage at the connector then you could replace the coil, if not, then you could replace the diode just to leave no stone unturned.

            This sounds like connector or screen.


            • #7
              I've been having issues with ZXW. It asks me to update or else I can't use it. Unfortunately the built in updater seems to crash and visiting the website gives me a security warning from my anti virus. Are you having any similar issues?

              I started looking at the connectors a little closer and it looks like you may be right after all about there being a bit of widening. I do see what I think may be some small cracks on it. When you first mentioned it I pictured this "widening" effect to be length wise along the connectors for some reason. I tried squeezing it back together a couple times but still no luck. I will be trying to replace it but I can't find the connector for sale on mobilesentrix. Is it compatible with that of another phone? Screens I've already tried a couple of different ones.

              Can you clarify what you mean about battery voltage at the connector? By coil you mean the backlight boost circuit coil/inductor?
              Last edited by computerprodigies; 09-20-2021, 06:12 PM.


              • Jessa_the_Professa
                Jessa_the_Professa commented
                Editing a comment
                ZXW--never use the built in updater. Whenever zxw makes a new version it breaks the old ones. Go to their website, download the latest version into a folder that you set as an exception in windows defender. Anti-virus will always think that zxw is malware. This is how it is for everyone--perhaps we are all now mining bitcoin for China, but I've never heard of any tangible ill effects.

                No need to replace the connector--just smush it. If that is the problem, it will be corrected by squeezing it. Worst case scenario--you may have to individually "pull" any connector pin that is slightly pushed into the center plastic more towards the outside edge of the connector. Show a detailed photo of the backlight area of your connector.

                Battery voltage at the connector--batt_vcc turns into vcc_main and vcc_main goes through the backlight coil (backlight boost circuit inductor) and proceeds through the diode out to the connector. If you have 4v ish at the connect it means your backlight circuit is not boosting. If you have 0v it means vccmain is not making it all the way there.

                Backlight will not be produced without a screen present, so you may have to solder a wire on the connector foot of the anode line to test.

            • #8
              Thank you. Unfortunately I can't download ZXW from the website as each time I try I get a "Secure Connection Failed" error. I cant seem to get around it. In the past I've been able to get it to load but sometimes it doesn't. I had the download hosts saved in history, one from a microsoft one drive and the other one from sendspace but when I download the file, it always fails at the very last second. When I try opening the file anyway, I get a request for password. Trying to get on the website to see if there was a password mentioned at the download page but can't get the website to load.

              Tried smooshing the connector with no luck. I tried doing it several times with no result. Unfortunately after the last couple of attempts the connector got a bit beat up. I measured for battery voltage at the anode connection using a piece of wire and the screen connected, I get battery voltage of aprox 3.8V. I still see the apple logo but still no backlight or boost voltage.

              Click image for larger version  Name:	2.jpg Views:	0 Size:	3.62 MB ID:	8413

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              Last edited by computerprodigies; 09-21-2021, 08:47 PM.


              • #9
                RE: ZXW. I just downloaded it and installed it on a new laptop. It works, but it is a pain. you have to first set a folder as a windows defender exception and then download it to that folder and extract from there. Otherwise, your antivirus will eat it. Even if you get it downloaded and installed if it's not in an exception then windows defender will eventually eat it. The onedrive link from zxwtools works.

                Re: the connector--on the backlight side, especially for the third pin from the end the connector pin has been pushed too far in. You can't see the center pin compared to all the others. Unfortunately this will require a connector replacement at this point. Be careful--heat at the connector has a habit of floating all the little filters and resistors buried in underfill near there. I was not able to see if your diode is on in the correct orientation--assuming you checked that.


                • #10
                  Thanks again!

                  I managed to install ZXW again by removing my antivirus all together. Making an excempt folder alone wasn't enough as it kept cutting the connection off every time I tried to download. It seems the only thing that was triggering it was the Update program included in the rar file. After re-installing ZXW and re-installing my antivirus however, none of the ZXW files show up as a virus if I scan the folder, weird. The only weird thing I did get was Microfish3.3 triggering a permissions warning with my anti virus. I just went ahead and allowed it.

                  As far as the issue with the phone. I replaced the connector. See picture below. Turns out the connector is the same as an iPhone 7. So display connector is compatible between 7, 8, and SE. Unfortunately the issue persists. Any other ideas? I may end up canceling the repair if the customer runs out of patience but would love to be able to fully trouble it.

                  Click image for larger version

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                  Attached Files


                  • #11
                    Replace backlight diode and coil, then you’ve rebuilt the whole circuit. Tell us which one was the failure. (These phones all use the same diode and coil)


                    • #12
                      Unfortunately no luck. I replaced both the coils in that area L5600 and L5100 as I wasn't sure which was the backlight coil. Looking at it now it looks like it's L5600. Do you know if both of these coils are interchangeable between themselves? IE can L5100 can be swapped in place of L5600? Either way I used a replacement from another phone for L5600. I also changed out the two diodes D5651 and D5650 and replaced chestnut and backlight IC again just in case I did something wrong the first time. I find no shorted capacitors around the area.

                      To make matters worse the phone is now boot looping. I'm not sure but it's possible that it was already doing that before but it was hard to notice due to the missing backlight. I wish I'd look closer before as it could be a clue to what the actual issue is. Via charge port the ammeter says it's drawing up to 2.1Amps and acts like it's getting ready to charge normally then after about 5 seconds the phone goes off and ammeter goes to 0, then it starts the cycle over again endlessly. Using the battery eliminator+power supply I get varying readings from around 73mA to around 200ma. Then the phone shuts off and doesn't try too boot again unless I press the power button. I'm still geting the dim apple logo during the moments the phone boot loops. I tried replacing the battery with no luck either.

                      Could any of the neighboring ICs such as the mesa and touch driver cause this issue too? Or any other suggestions you could throw at me would be great. Thank you!
                      Last edited by computerprodigies; 09-27-2021, 07:32 PM.


                      • #13
                        Chestnut and its coil--L5600 have nothing to do with backlight. Chestnut is a boost chip for image and touch. If you have image, then chestnut area is not the problem.

                        Backlight itself is always repairable---it's a simple circuit that consists only of the connector, the chip (U5650), the backlight diode D5650, the main backlight coil L5650 and that's it. Fault must be one of those.
                        Because SE 2020 is new, there may be more important role before in the selfie flash components that are part of backlight---selfie diode D5651 and selfie coil L5651.

                        Be sure your diode is in the right orientation, and because sometimes backlight coils don't like heat, try using an alternate coil like iPhone 5c backlight which is more robust just to rule it out. (i'm assuming the backlight coils are not embedded in an coil array (trinity chip) like in iphone 8, but if so then you have no choice but to reball trinity since the unique EEPROM is also part of that chip.


                        • #14
                          Unfortunately I had to give the phone back before I could figure it out. It was still a good experience and it was nice having some support along the trouble shooting process. Thank you!