In this mobile repair course, we addressed an unusual issue with a Redmi 8 device unable to make calls, displaying a message to turn off airplane mode. To begin, we disassembled the device.

At the 2:19 mark, we identified the RF IC under a shield on the right side. To access it, we removed the shield using 400°C and 70% air, employing high temperature and airflow for a short duration. We then found the problematic circuit, the U2500, which likely malfunctioned due to overheating.

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To fix the device, we re-balled the circuit by first removing it with a little flux, 380°C, and 40% air, using a JBC air station for power. We then cleaned the old solder with a de-soldering mesh, preferring to replace it entirely with new, high-quality solder. Upon inspection, we noticed that some pads were burnt, causing a loss of connection between the IC and the base plate and preventing the device from making calls.

We proceeded to re-ball the integrated circuit by removing the old solder with a soldering iron tip and using a compatible stencil to re-ball the RF IC. After applying solder paste and cleaning the area, we soldered the circuit with 350°C. It is essential to maintain a clean workspace.

Next, we soldered the circuit to the base plate using 380°C and 10% air, gradually increasing the airflow. To ensure proper soldering, we gave the circuit small taps; if it returned to its original position, the soldering was successful.

After reassembling the device and performing checks, we observed that the coverage was activated, indicating the device was functional. This repair demonstrated that with a solid foundation in mobile repair, no issue is too complex. The main challenge arises when a device has been handled by another technician, making it difficult to determine the device's history. However, by taking measurements on the base plate, such complications can be resolved.

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