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  • Troubleshooting A Dead iPhone CPU Repair

    Troubleshooting A Dead iPhone CPU Repair

    The CPU of mobile phones functions much like the brain of our body, making it a critical component.

    When it comes to mobile phone repair, addressing CPU issues can be quite complex.

    In this article, we will explore how to troubleshoot and repair a common problem with the iPhone 7 not turning on, attributed to pseudo soldering of the CPU.

    Problem

    1. No Response When Turning On the Phone

      • Press the power button, but there’s no response.

    2. Power Supply Test

      • Disassemble the phone.
      • Connect the phone to the DC Power Supply.
      • Press the power button.
      • The current pointer remains static at 50mA-60mA.
      • Connect the phone to a computer; the device cannot be recognized, suggesting USB IC or logic board power supply issues.

     

    Diagnosis

    To diagnose and potentially resolve the issue:

    1. Testing Power Supply

      • Remove the logic board.
      • Connect the battery connector to the DC Power Supply.
      • Test power button functionality.
      • Measure the 16 rails of the logic board power supply, ensuring the values are within normal ranges.

    2. Replacing USB IC

      • If power supply measurements are normal, replace the USB IC.
      • Attach the logic board to the PCB holder.
      • Carefully remove part of the shield plate.
      • Detach the USB IC using a Hot Air Gun.
      • Clean the bonding pad.
      • Solder a new USB IC and test; if the problem persists, proceed to troubleshooting the CPU.

    Troubleshooting

    Upon identifying CPU-related issues:

    1. Re-soldering the CPU

      • Remove the shield plate with a Hot Air Gun.
      • Apply high-temperature tape to protect nearby components.
      • Carefully detach the CPU from the board using a Hot Air Gun.
      • Clean the bonding pad and remove the solder from the CPU.

    2. Reballing the CPU

      • Position the BGA Reballing Stencil.
      • Apply Solder Paste evenly on the stencil.
      • Heat the solder balls evenly with a Hot Air Gun.
      • Allow the CPU to cool for 2 minutes.
      • Apply BGA Paste Flux to the bonding pad.
      • Position the re-balled CPU and solder it with a Hot Air Gun.
      • Clean with PCB Cleaner.

    Reassemble and Test

    Now that the CPU-related issue has been addressed:

    1. Reassembly

      • Install the logic board and the display assembly.
      • Connect the battery and press the power button.

    2. Testing

      • The phone should turn on normally.
      • Run a function test to ensure that all components are functioning correctly.

    Conclusion

    By following these steps, you can successfully troubleshoot and repair CPU-related issues in mobile phones. In this specific case, the iPhone 7 not turning on due to pseudo soldering of the CPU, our comprehensive process has resolved the problem, allowing the device to function as expected.

    Tools Used

    Free Schematic Software: Refox

    Visit our online shop for more parts and tools.

    You can also visit REWA YouTube Channel to check our video and learn how to repair a dead iPhone step by step.