iPhone 7 has been repaired by no serviecs

Machine Model: iPhone 7
Fault phenomenon: the mobile phone has been no serviecs

iPhone 7 has been repaired by no serviecs Figure 1.

Fault analysis: Insert card no serviecs, first check whether the machine has Baseband, *#06# can not output IMEI, and then check whether there is receiving and transmitting in the setting operator interface.
Maintenance process: After checking, it is determined that the machine fault is Baseband but not IMEI, disassemble the machine to check the motherboard,Baseband power supply has traces of soldering, reproduce and replace an Baseband power supply, and measure the ground value of Baseband around the Baseband power supply after the replacement, and found that The low ground value of LDO3 Baseband is only 240 Baseband, and it should be 430 Baseband normally.

iPhone 7 has been repaired by no serviecs Figure 2.

I thought there was a problem with the Baseband power supply that I replaced by myself. After removing it, the measurement is still 230 or so. Check the RF chip connected to the Boardview and the LDO3 VCC. According to the experience of repairing 6S in the past, it is judged that the large RF is easier to break.diode value or 230 directly remove the small RF, and the diode value returns to normal.