Solution: 1. After dissembling, we find the Wi-Fi chip has been replaced and there are enameled wires under solder pad. Therefore, the improper enameled wires and unqualified working condition may cause the trouble. 2. Remove the Wi-Fi chip directly and measure the diode data of each pin on solder pad. 3. Comparing with normal motherboard, the measured data is normal. When you after removing Wi-Fi, the measured diode data of PCIE bus is infinite. We can only measure whether the circuit is connected between PCIE bus and coupling circuit C0703, C0704, C0705, C0706, C0720, C0721.
4. Then, We find the circuits between solder pad and coupling circuit C0704, C0705 are open circuits through measurement. After checking the PCB circuit diagram, we find the circuits between solder pad and C0704 and C0705 will pass PP3169_RF and PP3166_RF.
5. Next, directly connect solder pad and test point with enameled wires, then paint UV Solder Resist . Reassemble Wi-Fi chip and test after power on. The Wi-Fi address still displays “unknown”.
6. Then, remove Wi-Fi chip again and measure the diode data of all pins on solder pad. We find the previous repaired places still in breakage. It connects or disconnects sometimes. In PCB circuit diagram, find the resetting pull-down resistance R0719.
7. Directly place enameled wire from resetting pull-down resistance.
8. Finally, reassemble Wi-Fi chip and test after power on. “About iPhone” displays Wi-Fi address. The trouble is removed. The tools we encountered in this article, you can find from vipprogrammer.com.