The iPhone 6 we are going to fix is accepted from customer last week, according to his description, the fault is no service on iPhone 6. It's been repaired before, but it's not fixed. The first step we are going to do is to diagnose the fault from 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. As shown in picture 8-3-4.
Finally, we put the removed RF IC back in iPhone motherboard, as shown in picture 8-3-5. The repairs end here!
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