Home » Cell Phone Repair Guide » iPhone Repair » iPhone 7 Series » Fix iPhone 7 Won’t Turn On – CPU Repair
iPhone 7 Series

Fix iPhone 7 Won’t Turn On – CPU Repair

Fix iPhone 7 Won't Turn On - CPU Repair

What should you do if your iPhone 7 won’t turn on after being dropped? The problem may be caused by a software crash or a complicated hardware issue. We have published an iPhone 6 won’t turn on and iPhone X won’t turn on guide video, and this time, we received an dropped iPhone 7 Plus which cannot turn on. The problem was finally detected as CPU being short-circuited. Here we have detailed troubleshooting procedures.

iPhone 7 won't turn on

iPhone 7 won’t turn on


Take apart the phone and disconnect the battery, then connect the phone with the DC Power Supply and press the 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.

fix iPhone 7 plus black screen

disassemble the phone and detach the battery

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.

iPhone 7 CPU short circuit

diode measurements on capacitors around power IC


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.

CPU SDRAM chip grinding

CPU SDRAM chip grinding


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

connect the phone with the DC Power Supply

connect the phone with the DC Power Supply

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.

Current reading on ammeter

current reading on the ammeter

For more details about iPhone 7 won’t turn on repair and iPhone repair videos, please check our YouTube video.

Need cell phone repair replacement parts or tools? REWA offers wholesale and retail mobile phone repair parts/tools with affordable prices for 10 years. Welcome to check our online store shop.rewa.tech.

a new way to fix iphone 7 plus button
A New Way to Repair iPhone 7/7Plus Home Button
Find The Faulty Component With Rosin - iPhone 7 Plus Won't Turn On Repair
Find The Faulty Component With Rosin – iPhone 7 Plus Won’t Turn On
How To Repair iPhone 7 Touch Screen Not Working
How To Repair iPhone 7 Touch Screen Not Working
  • Ashi
    01/07/2020 at 7:08 pm

    Hi Team,
    Iphon6 CPU has broken due to physical damaged, possible to repair and take the back up from phon.

    • REWA
      01/11/2020 at 3:35 pm

      Data recovery needs the CPU, Logic board EEPROM, NAND flash, baseband CPU/ EEPROM IC do not damage.

  • Arthur Wu
    11/14/2019 at 3:51 am


    I watched your video on how to fix iPhone 7/plus won’t turn on issue at https://www.youtube.com/watch?v=eMYQ8oaIHO8

    The job is a amazing.

    My iPhone 7 Plus 256GB seems having the similar symptoms:
    * Can’t turn on
    * I have to shake it very hard, and it might turn on, but the screen turn into color lines, and then shut down, and won’t turn on again
    * I will have to let the phone sit for a long time, let the battery drains. Then, probably, with another shake, I can turn it on, just by luck.

    Some questions:
    * How can I get the SDRAM?
    * How much does it cost?
    * Is it fully functional?
    * Is the SDRAM where all the data stored?
    * Instead of using the CNC machine, can I just use hot gun to melt the solder to remove the SDRAM?

    Thank you!

    Arthur Wu

Leave Your Reply