According to the attached file, we found there happens a ineffective touch, we use a replaced screen to test it, but still no works, so we may need to disassemble it.
The bottom of the UMT board is easy to be disconnected, so we plan to dealt with the no- touch fault at first. There are two ways to take the IC: one is to take out with tweezer; the other is to pick up from the side of IC. After removed the iPhone touch IC, reinstalled the machine, and the phone boot White Apple restart, turn on start current run at 300mA.
Picture 1
We haven't repair other place else, only remove the touch IC and check the resistance of the bottom of the board. The resistance is normal after tested by digital multimeter, such problem we haven't meet before. I am a little anxiety see the fallen UMT. Since the start current is too large, take U2 down and look at the starting current, he result is the same without any change. Measure the resistance value of U2 pin habitually.
Picture 2
We found that the PP3.0V on F4 pin is short-circuit, and this line has a large power supply, fingerprint power supply and U5411_RF of the head.
Picture3
Power-up again, we found U5411 - RF heating, disassemble the two components connected with U2, then turn on, we can determine the damage is caused by U5411. Turn on, the iPhone jump from 300mA and White Apple does not enter the system, after replaced U5411, the problem was being resolved. Install the touch IC and test function, occurs a new fault. There is no service after turned on, and no serial number. For this fallen UMT motherboard baseband failure, we remove the baseband CPU directly with QUICK 861DW Rework Station, then the fault will be resolved through welding wire on the left upper left V1, U1.
Picture 4
Finished solder a wire well, then apply UV fluxes oil, re-plant tin on baseband CPU, and installed , finally, test function, all is normal. Repair work finished successfully.
Nice post, thanks for sharing this informative article.
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