Russian
Spanish
Portuguese
☝️ How to disassemble this smartphone, you can see our detailed instruction: link
1️⃣ Problem Identification:
One of the most common issues with network loss on this model is water ingress through the SIM tray gap under the modem shield.
The water often affects the switch IC located at the edge of the board.
Using a soldering station, carefully remove the metal cover and inspect the damaged components.
The photo shows that only a small amount of water has entered, but it's enough to cause issues.
2️⃣ Cleaning the Damaged Components:
Use a brush with a degreaser* to thoroughly clean the damaged areas from oxidation. Even though everything looks fine visually, the network is still not working.
*cleaner and degreaser with high impact action
3️⃣ Removing the IC:
With a hot air soldering station, lift the IC. It's immediately noticeable that the contacts where the voltage is supplied have burnt off on both the board and the IC.
4️⃣ Restoring Vbat Power:
The Vbat voltage* can be supplied from the nearby capacitor. Use a thin copper wire to connect the capacitor to the missing contact under the IC.
*voltage from the battery
5️⃣ Applying UV Mask:
Apply UV mask to the restored contact and place it under a lamp for curing. Under a microscope, the contact on the IC was successfully restored, and it was re-balled without any issues.
6️⃣ Removing Flux Residue:
Use Flux-OFF* to clean off the remaining flux and prepare the area for soldering.
*a balanced mixture of solvents, quickly and reliably removing flux and other contaminants after soldering
7️⃣ Soldering the IC:
Solder the IC back in place over the restored contact.
8️⃣ Testing:
Reinsert the board into the phone and check the network. The network indicator is now showing, 4G is working, and the signal strength is full! 👍
If you have a question, ask us, and we will try to answer in as much detail as possible. If this article was helpful for you, please rate it.