I would try these steps in order.
1- Open the phone, take out the board and check ( J1111 ) if it's damaged
or shorted repair it. Try to restore the phone without connecting the
front camera flex.
2- Check ( U0301 ) IC if it's cracked or damaged, resolder or replace.
3- Take out the board and remove the metal sheild over the NAND chip
(the U0604 chip in the picture). check if ther is any damaged component
around the chip, or if there any water damage (clean it ).
Check if there is any shorted (capacitor, resistor, coil) around the chip
then replace it.
4- resolder the NAND chip using heater (use the same tempereture you
use usually to remove ICs). heat for about 15 seconds and don't forget
to protect the ICs around the chip.
5- Replace the NAND chip but be carfull ( don't heat to much cause you
got the CPU in the other side). Don't go to this step befor being sure
that you did all the previous steps and there is no problem connecting
to Apple server.