Why is the iphone 7 not turning on

The iPhone 7 isn't turning on.In this article, I'll help you diagnose why your iPhone 7 won't turn on and show you how to fix the problem for good.

Disassemble the iPhone 7 and connect DC power supply to have a test, the restart current stuck at 50mA, and the device can not be online.

As we have repair experience on iPhone 6 generation, 50mA current is often related with CPU, U2 and display power preoblems.

Considering the online failure, we replace U2 chip first, the result is the same.
Disassemble the CPU shied cover and observe the iPhone 7 CPU chip under Stereo Microscope, we found the CPU attached well without any track of cracks. 50mA is unable to measure the voltage, so we have to first measure the resistance on the circuit of restart conditions. After the iPhone 7 CPU and NAND are measured, continue to measure clock, reset and bus.

The fault is from the clock. The output resistance of the first pin of 24M main clock is only more than 200, the normal value of the first and third pin should be more than 800. As shown in picture 17-3-1.

Picture 17-3-1

First remove the associated capacitance C0702, the result is same, so the surrounding small resistance is necessary to be replaced, directly take the main clock to measure the bottom pin (quickly taken down at high temperature , we use QUICK 861DW Hot Air Gun with straight nozzle at 420 degrees.)

The resistance of bottom is all normal. Replace a 24M main clock (common used on 6S). After replacement, it can connect online, and also normal for iOS flashing.

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