iPhone stuck in a restart loop, the phone continuously restarts and became totally unusable, the Apple logo appears and disappear, over and over again.
The repair steps as following:
1. Take down the LCD screen assembly
2. Test voltage of the battery with the digital multimeter. Battery voltage is 4.21V, battery test signal voltage is 2.02V. The battery is normal, so we install the LCD screen assembly to check other malfunctions.
3. Failure detection: connect the phone to computer, it could not be restored by iTunes, an unknown error occurred (9) so that we can draw a conclusion that NAND flash or CPU is cracked.
4. Detach the motherboard from the phone, and fix it on PCB holder.
5. Remove the NAND flash chip from motherboard carefully.
6. Clean the bonding pad with the soldering iron, knife, BGA paste flux, rosin, solder wick and PCB cleaner.
7. Connect the NAND flash programmer with the computer, transfer the data from the old NAND flash to a new one.
8. New NAND flash chip BGA rebelling.
9. Install the new NAND flash chip to the motherboard.
10. Install the motherboard to the phone.
11. Connect the phone to computer, it can be restored by iTunes successfully.
12. Test if it works well.
