Phone water damage would cause all kinds of malfunctions. Here we have a Samsung A70 that gets a flicking screen because of water damage. How to fix it? We will give a detailed demonstration here. Phone water damage repair is quite difficult. If no traces of corrosion, we must measure and analyze to find out the cause.
The flickering screen could be caused by the screen itself. Therefore, the first step is to replace the screen. Disconnect the battery, the screen BTB, take down the screen. Then install a new screen.
After screen replacement, we test again. However, the blue light still exists.
Main Flex Cable Replacement
If the main flex cable has been damaged, the flickering screen also might happen. So we try to replace the main flex cable. Connect the SUB port to the sub-board, and the MAIN port to the motherboard, and connect the flex cables and battery.
However, when we boot up the phone, the screen is still flickering. We conclude the motherboard has been faulty.
Which parts of the motherboard need to be checked?
The display circuits include a power supply, clock, reset, and data. Clock and reset signal faulty will cause the phone no display. While the power supply and data faulty will cause distorted display. Therefore, if the phone screen display distorted pictures, we just need to check the circuits of the display power supply and data.
We decide to check the display power supply circuit, the display PMIC
Display PMIC Testing
The display PMIC lies inside of the motherboard, thus we need to separate the motherboard to test it.
- Take down the flex and sub-board
- Take down the motherboard
- Fix motherboard on the PCB holder
- Set temperature to 200℃ and heat up the BT, then take down the BTB buffer foam
- Afterwards, at the same temperature, heat up and remove the cooling foil on the shield cover
- Set temperature to 380℃, wind power 40, and heat up the tin around the shield cover for about 60s
- After the tin melted, take down the shield cover with tweezers. Please do it carefully, or the motherboard parts could be removed by the shield cover.
Find the display PMIC with the help of the motherboard inode bitmap, then measure the large inductor around the IC.
As a result, the LED- grounding diode reading is 0, normal. While the LED+ is also 0, abnormal. Apparently, the display PMIC has been faulty. We need to replace it.
Display PMIC Replacement
Three steps for display PMIC replacement:
- Apply some solder flux on the display PMIC, and heat it up at temperature 360℃, wind power 40. Then take it down.
- Pick up a spare A70 motherboard, and take down its display PMIC in the same way.
- Weld the backup display PMIC on the faulty motherboard. PS: since there are few welding spots on the tiny IC, and the welding spots are even after taking down, so no need for GBA.
The display PMIC has been replaced. We install the phone and test again. Needless to say, the screen has no flickering anymore. Problem solved.
Please check the detailed operation here: