HELP! My iPhone 6S Plus no service, what can I do?

 Yesterday, we got a message from our customer, he said his iPhone 6S Plus has no service, even if the phone is restarted, it doesn't work. So, he send the phone to us.  After we check it,  the phone cannot recognize the SIM card, but it can search the operator manually. We suspect that this problem was caused by the launch part.

Disassemble the iPhone by phone opening tools, and carefully take out the motherboard. Using multimeter to measure the diode data of PP_1V85_SMPS4, the diode data only have 59, as shown in picture 1. Because this voltage is supplied to RF IC, so we remove the RF IC.

 

After we remove the RF IC, we measure it again; the diode data back to normal. So we replace the new RF IC on it, we can check it under the microscope, as shown in picture 2.

 

Now we turn on iPhone, and test it, the signal is back. However, during the testing process, we found the 3G shows no signal, when we choose 3G signal, it will be no service, 4G and 2G is normal.

Other signal all is fine except 3G; this trouble is mostly caused by the UMBPA_RF. After we replace the new UMBPA_RF with phone rework station, 3G signal is normal.

Finally, test other function on the iPhone 6, all is fine, the repairs are over!

Troubleshoot: there is no service on iPhone 6

Customers sent us an iPhone 6 to repair; the faulty is that there is no service on iPhone 6. It's been repaired, but it's not fixed.
After we received the iPhone 6, we started checking the iPhone. We can't find the operator in manual condition. As shown in picture 8-3-1.

 Disassemble the iPhone 6 by phone opening tool, take out the motherboard, we can found that the colleague has been repaired RF parts, now we need to fix it step by step.

Let's start with the easiest. Soldering jump wire on U1、V1 pin, still no service. Because the colleague repaired too many chips, as long as the chip on the RFFE bus has problems, it will affect this. Remove all chips except 2G power amplifier on RFFE bus, the iPhone still no service. Then we replace the antenna switch and RF IC, the problem still the same. It seems that colleagues have amplified the problem.

Now we use multimeter to measure the power supply on RF IC U_WTR_RF, we found that the resistance at both ends of the R38808_RF resistor on VDD_XO_2V power supply is incorrect, one side it 438, the other side is 564. U_WTR_RF and R38808_RF in the circuit diagram position as shown in 8-3-2 and 8-3-3.

When we use multimeter Lead Probe to press it, it's back to normal, so we can judge that the resistance is virtual welding. Now we find the problem, so we solder it with soldering station. After finish it, we assemble the iPhone and test it, the signal was back.
Finally, we put the removed RF IC back in iPhone motherboard. The repairs end here!