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Solution: iPhone 7 Won't Turn On Failure

We received an iPhone 7 device from customer, it is not turning on. This is a common failure for iPhone repair technician. How to test and repair the failure step by step? Let's check in the article!


Tear down the iPhone 7 and connect DC power supply to test, the reboot current stuck at 50mA, and the device can not be online.

We also met the same situation on iPhone 6 devices, so we know the 50mA reboot current is often related with CPU, U2 and display power problems.

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 CPU and NAND are measured, continue to measure clock, reset and bus.

We found 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 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 ok for flashing.

More iPhone repair tutorials, please feel free to contact on www.vipfixphone.com

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