Xiaomi Mi 9 Not Turning On Issue Repair
Model: Xiaomi Mi 9
Announced: 2019, February 20
Case 1
The phone back case has been replaced before and can boot when pressing the motherboard.
Based on the repair experience, it should be the power IC U4200 and U4700 poor soldering.
Take out the motherboard and heat with the hot air gun to reflow the two chips.
(As there are two openings on the shielding cover, no need to remove the cover.)
Cool down the motherboard and then assemble the phone to test the function, it works fine.
The issue gets resolved by reflowing the two power chips.
Case 2
Cannot boot issue, and it has been repaired in another repair shop before.
First, check the motherboard carefully, and find the U4200 and the U5200 have been resoldered before.
Try to resolder the two chips
- Heat with the hot air gun to remove the two chips
- Clean the pads on the PCB with solder flux and solder wick
- Reball the chip then solder it back
After the resoldering process, assemble the phone to have a test. The phone still can not be booted.
Based on repair experience, the power IC is a common issue, chip damage or poor soldering can cause
- Won’t turn on
- Sometimes can turn on, sometimes cannot turn on
So let’s remove the two power IC first, then replace another two with the same specifications.
After the chip replacement, let’s solder back the shielding cover assemble the phone, and have a test. The phone can be booted normally and all the functions are tested OK.
Summary
The Xiaomi Mi 9 cannot boot is a common issue, might be the board design problem. The power IC like U4200, U4700, and U5200 are easy to get poor soldering or damaged. For the won’t turn on issues we can resolder them or replace them directly to repair.
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