First, disassemble the iPhone and energize the motherboard. The DC power supply displays 1.7V current that is short circuit and the adjustable power supply voltage is pulled down to 3.4V. The whole motherboard gets hot, especially the main power drive chip .
Second, deenergize it and measure the power supply of each circuit at motherboard through digital multimeter, find that the power supply of PP3V0_NAND of EEPROM is short circuit to ground and the resistance data is 0. The test points of PP3V0_NAND are shown in picture 1-1.
Third, use solder iron to make rosin in the capacitance which connect PP3V0-NAND, then slowly turn the current button of adjustable DC power supply to increase the current limit, the inductor that is connected with PP3V0_NAND melts when the current is 3A. Therefore, this inductor is short circuit. Deenergize it and remove this inductor, as shown in picture 1-2.
Fourth, after removing this inductor and plugging adjustable power supply, it is not short circuit. IPhone can get into IOS normally. Remove a inductor from the same place of the accessories pad to replace the old one. This problem was been solved.
As this 3V voltage is parallelly connected many capacitors. It will take long to tear them one by one. Thus we use burn-in method to find the short circuit point. Put rosin on motherboard and set the adjustable power supply to 3V. Adjust the current limit to the lowest. Connect the negative pole of adjustable power supply to ground and connect the positive pole to the short circuit point. Then energize it. Slowly turn the current button of adjustable DC power supply to increase the current limit. The place that rosin melts fastest is faulty.