Chosen Solution

Hi Community, Got a phone given to me of a repairer. Original repairer killed the phone after a screen replacement. I have managed to get power to return to the device after a tristar change, however, the phone now boot loops into DFU mode. I have attempted restore via itunes and it returns an error similar to “cannot find device” and using 3U which returns two errors: “Unable to switch DFU mode to recovery mode” however phone goes into recovery mode, so i try flash again and get the next error"Invalid serial number" I have checked for any other errors on the board with nothing visible, no heat, tried restoring with no screen, new screen, new charge port, different cable and different PC all with no luck. Any ideas would be great!! Update (12/08/2017) Anyone got any more info on this one?? Does anyone know which IC the serial details are stored in? I did have to replace the ‘5750 intermediate frequency IC’ , but dont see that having any impact on this….?

So today i decided to get working on the iphone 7 again. Plugged it into my computer, same old errors. I just had an incling to try again on my mac (had tried in the past), hey presto…. the phone restored nearly the whole way and then threw error 3 towards the end. Best thing was, when the phone reconnected, it had its serial number back again. I plugged it into 3u and the phone started to restore again correctly, however, now is hanging at baseband install. More digging to do!!! But thanks for the answers so far!

From what I have read (Not from experience) it is most likely caused by either a corrupt NAND or from overheating NAND during Tristar and caused bridge or cold solder joint. If you have the NAVIPRO 3000, you could remove it, reprogram and install, if not, you could reball and try again. But this is from “Reading” about the issue and could be wrong…just an idea and would seek out expert advice from @refectio or @jessabethany before going to such extremes. I did read on one post that to remove FMI if on but not sure if that would cause a SN issue. Please repost answer you find I’d be interested in knowing what repair worked for you

I would continue looking into the charging circuit. Boot loops, annoying, can happen from charging circuit issues. After that I would look into the voltage rails coming out of the pmic. You’ll need a zxw tool for that. They’re not expensive, and worth their weight in gold

Hmmm… Plugging the cord into the pc BUT NOT THE PHONE. then as your holding down the home button plug the other end into the phone. THIS WILL RESULT IN DATA LOSS!

Check nand reset line that was the culprit