Mensagem original de: arbaman ,
If you had to replace the back housing I would think the iPhone took a bad hit and it would be quite likely the issue was already there before replacement and/or the handling of the board made the damage just evident. No service flag with request to update is typical of a hardware damage to the logic board where the processor can’t find the baseband. It could be due to a number of components and will require deep microsoldering skills to be fixed. The only thing you can try is a DFU restore, but there are serious risks it won’t complete and phone will be stuck in restore mode until fixed.