Easy Guide: How to fix iPhone 7 Plus Multi Fault Problem

We received an iPhone 7 plus, after disassemble and test, we find this iPhone is severely corroded by water. In this case, we can't clean the phone blindly; we should observe the corrosion under a microscope first, and then the corresponding phone schematic diagram to understand the role of corroded components in iPhone.

Rip off the motherboard sticker that can be ripped, and remove the iPhone PCB shield cover that can be removed. According observe, we find the most serious is the display backlight part. Now we can clean the iPhone motherboard first, and then measuring power supply C3405 with multimeter, it directly to the ground, careful observation under the microscope found that C3722 was severely corroded. After removal, the diode data of the main power supply becomes 298. At this time, connect it to power and phone standby leakage 30mA, press the iPhone power button, the iPhone screen is lit, but the left screen is dark. Leave it alone, enter the IOS, and insert the SIM card to test, we find there is no 3G、4G， the fingerprint is normal. It not only stuck on fingerprint setting, but also the restore network, restore all settings. Observing it under the microscope, we found that FL3901 corrosion seriously caused the left iPhone backlight IC cannot supply power. After soldering jump wire, it's back to normal. Picture 10-2-1

Then found R7109 corrosion damage caused the power supply to high-frequency power amplifier circuit impassability, resulting in no 3G and 4G.  After soldering jump wire, it's back to normal. Picture 10-2-2

Now we're going to solve the problem that stuck on iPhone. We want to backup first and then brush iPhone, then we found it can connect to PC, but when you connect to iTunes, it times out, dis U2 cause it? So we replace it with iPhone 6S U2 IC, but the problem still exists. So now we directly use DFU mode to forced brush iPhone.

However, when the progress bar shows 60%, it reports unknown error 56, re-flash several times, it still the same, the unknown error 56 most caused by NFC. iPhone Baseband CPU、camera power supply could also cause the problem, but these function all is normal, so we judged NFC. Observing NFC under the microscope, we found that it had a little corrosion. Picture 10-2-3

Remove the NFC, and measure the diode data of NFC, we found the G2, D5 and C7 all is connect to ground. From the phone circuit diagram, these three points are connected to the NFBST_RF, as shown in picture 10-2-4, we directly remove it, G2 still short circuit. After remove the C7517, the resistance is normal; D5 and C7 also back to normal. Replace the chips on motherboard, and weld well, flash it again, it still reports unknown error 56. Water-damaged motherboard power supply is the easiest to burn, so we remove shield cover of iPhone CPU.

It can be seen from the schematic diagram, there is a group of power supply PP_VDD_MAIN_NFC converted by NFCSW_RF which from main power supply, so we can weld the jump wire from the A1 pin to the A2 pin. Picture 10-2-5

Brush the iPhone again, now it can be successfully brushed iPhone. Enter the IOS system and test all functions, now it is not stuck on iPhone fingerprint setting, seems it was caused by system issues. Now, the iPhone 7 Plus has been repaired! Picture 10-2-6

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