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☝️ For a detailed guide on how to disassemble this smartphone, check out: [how to disassemble Xiaomi Redmi 12]
⚠️ Before disassembling, do not forget to turn your phone off.
We heat the back cover to 50°C or 140° F and carefully pry it open.
Upon inspecting the motherboard, we notice that the water only reached the area under the metal shield on the upper part of the main board.
When connected to a lab power supply, it shows a short circuit on the board.
1️⃣ We desolder the metal shield and see that water entered through a small hole, directly onto the power controller (Mediatek MT6358VW), and moss has grown around it 😂
2️⃣ Using a soldering station, we remove the power controller.
There’s a lot of dirt underneath and around it. Additionally, two nearby capacitors are blown and are causing a short circuit across the entire line.
3️⃣ Fixing this is relatively straightforward, but while cleaning the pad under the controller, we discover a burnt-out contact. This makes things a bit more complicated.
4️⃣ Using a scalpel blade under a microscope, we carefully clear away the burnt PCB material to expose the contact in the second layer.
5️⃣ With the finest soldering tip, we tin the remaining contact in the second layer.
6️⃣ We take a very thin copper wire and solder it to the exposed contact. Then, we apply UV mask to secure the soldered area.
7️⃣ We shape the remaining wire into a contact pad.
8️⃣ We re-ball the controller, apply flux, and reattach the chip to its original position 😊
9️⃣ Using a multimeter, we confirm there’s no short circuit. Then, we connect the board to the lab power supply and check its response to the power button.
Finally, we reinstall the board into the chassis and test it 🙈
The phone turns on! We reinstall the capacitors, the metal shield, and the cameras.
We test all the phone’s functions and fully reassemble the device 👍
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