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Fix iPhone 7/7 Plus Can Not Turn On - CPU Repair

Fix iPhone 7/7 Plus Can Not Turn On - CPU Repair

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Video Introduction
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iPhone 7/7 Plus won't turn on after it is dropped? Due to the imperfect technology of CPU supplier, the SDRAM of iPhone 7/7 Plus series can be easily damaged. Once dropped, the SDRAM might be short-circuited and the phone won't turn on afterward. Let's click the video to know how we fix iPhone 7 plus won't power on the issue in a more efficient way.


Diagnosis


Take apart the phone and disconnect the battery, then connect the phone with the DC Power Supply and press power button to power on. The current reading of the ammeter jumps to 350mA and then stays still, which is abnormal and indicates that the logic board is short circuited.


Disconnect the power supply and take out the logic board. Run diode measurements on capacitors around power IC one by one. All the values are normal except  C1823 – It displays 0, which indicates that C1823 is short-circuited. From the schematics, we can see that C1823 is the filter capacitor of PP1V8-SDRAM, and it is directly connected to CPU SDRAM.


Attach the logic board to the PCB Holder, and take down the shielding cover by heating with Hot Air Gun, then remove CPU SDRAM with CNC Chip Grinding Machine. After chip grinding, attach the logic board to the PCB Holder and clean it with PCB Cleaner, then remove the black adhesive around with Sculpture Knife. After that, apply some BGA Paste Flux to the bonding pad. Align the new SDRAM to the right place(Don’t reverse the direction),  and then solder with Hot Air Gun. After cooling for 5 minutes, clean thoroughly with PCB Cleaner.


Testing


Connect the phone with the DC Power Supply, then short Pin 13 of J4504 to the ground with tweezer to trigger the power on system. This time, the current reading on the ammeter is normal.



Get the logic board assembled and buckle the display assembly. Connect the phone to the computer, then press and hold volume down and power button to get into DFU mode. Restore the phone via iTunes. Once done, insert the SIM card and activate the phone. After testing, All the functions work normally.


If you want to see the detail by pictures please go to REWA Blog We have published  iPhone 6 won’t turn on and iPhone X won’t turn on guide video


Tools Used:

DC Power Supply

Digital Multimeter

Integrated Mobile Phone Repair Platform

PCB Holder

CNC Chip Grinding Machine

Screwdriver

Solder Wick

Solder Wire




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