Malfunction Phenomenon
The phone had been dropped before, it kept on booting loop and showed error code 4013 when restoring it with iTunes.
Trouble Shooting
For the iPhone X Error Code 4013. Because the phone was dropped before, the possible reason might come from the connection between the top and bottom layers, especially the connection related to CPU or Baseband.
Take out the motherboard and connected it to the DC power supply machine to check the current, the current reading on the ammeter was normal. Then detach the two layers, and we found there was a crack on the middle frame nearby the SIM card connector, and some of the pads had been lost.
Check with bitmap to find out the pins which were useful, and apply the jumper wire method to fixing the bonding pads that had been missed.
After fixing the missing pads, then we used fixture iSocket to test, the function back to normal, no boot loop anymore. Then solder the two layers of motherboard together and restored. The phone can be restored normally, the problem was resolved.
