Malfunction Phenomenon
Power on the phone and check, SIM card cannot be recognized and no service.
Restart the phone and test again, the SIM card still could not be detected.
Trouble Shooting
Normally, most iPhone 7 No Sim Card Issue was caused by the detective pin on the SIM card reader, and sometimes it might be caused by 2G Power Amplifier and baseband CPU.
First, we checked the appearance of the SIM card reader detective pin, and we found a little bit water damaged trace on the pin, clean the motherboard with PCB cleaner thoroughly, and tested again, problem resolved.
Summary
From this repair case, we can see sometimes the motherboard chip level is not so difficult.
Just need to follow the basic repair rule, from the easy part to the difficult, from the outside to inside, from check the appearance to measure diode/voltage/current value.
Plus with enough good repair handwork like soldering, jumping wire, etc. Then the cause can be found and the issue can be resolved gradually.
