Wise Way for iPhone 6 No Reply

Fault Description:

No series number shows up when dialing *#06#  and kept searching state without signal.

First step is to disassemble the basic, we found  iPhone 6 LCD Screen was replaced ever, we doubt there occurred an Baseband CPU false Welding error, Following our repair process:

From the simple start, measuring the single iPhone 6 motherboard baseband power supply, first measure the main power supply 4.2V (C3221_RF)

                                                                                              14-7-1

Then testing baseband output voltage of power supply on C3262, C3252, C3259, C3256, if there is a voltage without first measuring resistance, if resistance is normal, then replace normal baseband power test; if four of them are simultaneously without resistance, then you need to reinstall the baseband CPU. There is a small glass tube base strip above the baseband power supply, it must be noticed when the main board is disassembled, if it gets damaged, the iPhone 6 will not be repaired.

Before the iPhone 6 CPU is removed, we must deal with the shielding cover carefully. We need to cut it off with professional cell phone repair scissors. This is relatively safe. The shielding factory is very strong in welding, and the risk of heating and blowing is relatively large.

The baseband CPU can be mounted on the fan to avoid heating IC.  It doesn't matter if you see some empty solder points. It takes two parts to solder jumper wire on the pad: U1 and V1 pin.

14-7-2

It may be okay to see two points on the naked eye, but under a Trinocular Stereo Microscope, it will be found that the two points are at the top of the layer, and the line is very thin. Sometimes there will be baseband faults when the line is disconnected. For the sake of insurance, solder jumper wire first.

14-7-3

The small U is thicker. When do CPU reballing, you can cut out a small square on the paper towel and put the small U in it. After installing the baseband CPU, you can first test the C3402_RF to determine whether whether the baseband CPU is installed ok.

After we confirmed it again , boot it. Both baseband and signal shows normal!