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

• Hot Air Gun Rework Station – 990AD
• Integrated Repair Platform
• Digital Multimeter
• Communication Maintenance Power Supply
• Electron Microscope 

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.