Defective Phenomenon
Received an iPhone 11 Pro no service and keep searching network issue.
The issue happened during normal use.
Troubleshooting
Double check the issue, the defect phenomenon is the same as customer described. Insert another SIM card to test, no signal and keep searching.
Dial the *#06# and the IMEI number can be displayed.
Which means the RFFE relative rails should be OK.
And can also find the available operators at Setting > Cellular > Network Selection
Based on the above information, we can judge the reception process relatd parts should be OK.
The defect phenomenon should be caused by the transmission related part.
Repair Process
First, Disassemble the phone and take out the motherboard.
Then put the motherboard in the heating platform. Power on heating and seprate the two layer of motherboard.
After that, measure the diode values of the bonding pads on the middle frame.
All diode values are OK.
The we just go to the transeiver IC (XCVR_K) directly.
Apply some rosin around the chip, then heat with hot air gun. When the tin on the pads get melted, hold the chip with tweezer and take it off slightly.
Once the Transceiver chip get removed, we can measure the diode values on the PCB pads.
And the measured diode values on the PCB are also OK.
So based on the repair experience, let’s replace the XCVR_K chip with a new one.
For the XCVR_K chip, we can find the specification from schematic (PMB5765-B2), or from the surface of the chip directly.
Find the exactly same spec. chip to replace, and when you solder it back please pay attention and do not reverse the chip direction.
Test
After get the new XCVR_K chip replaced, put the motherboard into the test fixture to test. Service back to normal, with 4G sign and can make phone calls normally.
Issue get fixed by transceiver replacement.
