Defect Phenomenon
An iPhone 6s with water damage, and when connected with 4G network the iPhone 6s cannot make phone calls normally.
Troubleshooting
Normally, when we make phone call with 4G network connected, there should be 4G signal bar displayed on the screen. But this phone displayed nothing on the signal bar.
Since it’s a water damaged phone, so we should check the water damaged part first. And based on the repair experience, making phone call failure with a high chance is caused by the 2G amplifier IC () get damaged.
Repair Process
First, let’s disassemble the phone, and we find the cooling paste sticker is gone. Obviously this phone has been disassmbled or even been repaired before.
Besides that, we can see the small components around the shielding cover is dirty and with corrosive signs. So just tearing down the shielding cover on the signal related chips, and go for the 2G amplifier IC directly.
Remove the chip and measuring the diode values on the PCB pads.
After measuring, there is no diode value on the pin 8. The pin is the power supply pin for the 2G Power Amplifier IC, normally, the diode value should be around 300!
So there must be some components which related to the pin 8 with problem. Check the bitmap and schematics
It’s related with R4501_RF, C4501_RF, C4503_RF. The three components.
And among them, the resistor get corrosived very seriously. We can remove it with tweezer slightly.
So go for it! Replace the R4501_RF with a new one. Then measure the diode value on the pin 8 again, it’s back to normal.
Then solder back a new 2G PA IC, assemble the phone, and make phone calls to test again.
Phone call function back to normally.
Cannot make phone calls issue get resolved by the resistor replacement.
Summary
The water drop damaged phones are not as difficult as the drop damaged phones.
We can always start from checking the cosmetic carefully and deal with the abnormal components. Maybe the serioud issue can be resolved by a small operation!
