Checking and observing, we got the faults. The phone motherboard happens short circuit after being dropped into water.
And then, we disassemble it, and find that the power supply IC is corroded, so we may need to check the current carefully.
After cleaning the corroded part, it still won't turn on. The leakage is 6 Ma and the starting current is 50 ma by measuring with DC power supply.
Due to the fact that IC is more likely to cause this failure, we are going to remove it to retest, the problem is solved now. Then replace the display IC and install to test function.
All functions are normal, but it can not charge and also can not connect to the computer now, after replacing U2 u2300, fault still exists, then remove the shield cover, measuring its IC side circuit, we found that the end of the capacitor c2300 corrosion blackened.
Picture 1
After checking the drawings on WUXINJI dongle, the capacitor can not be removed because it is not a ground protection capacitor, but a coupling capacitor on the TIGRIS-BOOT circuit.
Picture 2
Finally, directly replace an old iPhone 6s motherboard with a good capacitor and replace it again, the problem is finally solved now.
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