Blue Screen / Bootloop / Black Screen "Not" U6 Long Srew Related

Hi Guys,

Hope you can help..

Shortly before Christmas I was tasked with refurbishing an iPhone 5s for a client. On pre-testing the phone (which already had a damaged LCD) I noticed it wouldn't charge, in fact my first charging cable used burnt out. I ended up changing the charging port assembly and battery, at which point the phone began to charge.. The next problem happened when I came to boot the phone, the Apple logo appears, the screen dims as its supposed to.. then a blue screen would flash and then just a black/blank screen. however, I spent a lot of time going through DFU and trying various suggestions from forums, I also removed the U6 screw holder to inspect for damage beneath, There is no visible damage to the circuit board, so I re-soldered it back in place, and after lots of fiddling & messing about the phone started to work and I continued with the refurbishment.. Two weeks later and the phone has fallen over, it will boot intermittently but 9x out 10 you will only get the blue flash and followed by a black screen..

Are you aware of any particular components like the U2 IC chip or other that may be causing this issue, has anyone successfully rectified this issue.. also, some links to some schematic diagrams of the iPhone 5s logic board would also be very helpful..

Many Thanks in advance..

Paul