Press the home button, we can see the display is working.Pry out the back cover with a pry bar after heating it for a few minutes.Take it down.
Apply a protection sticker on the camera module.Unbolt the screws for fixing the motherboard.Take the fixing cover down.
Disconnect the flashing light flex cables with this pryer, and the battery cable, the display cable, the charging cable,the power cable, the earphone jack cable and the sensor cable.
Take down the camera module,the motherboard.
Prepare a new screen assembly,install the motherboard.Connect the display cable, the charging cable, the power cable,the earphone jack cable and the sensor cable.
Turn it around,power on,wait for a moment.Now we test its touching function–it’s not working.Power off and try again, the problem still exists.
Turn it around,disconnect the battery cable, the display cable,the earphone jack cable and the sensor cable.
Take down the motherboard,observe the display connector and other connectors.Now let’s see this brief diagram of Huawei mate20 touching connector’ pins.
Their resistances are as demonstrated:
Next we are going to measure the resistances of each pin with a multimeter and see if there is any abnormality.
J1701 Pin 37, no reading, while its normal value is 450.
Move on, all performs normal.
Measure J1701 Pin 37 again, still 0.
This circuit connects a resistor R1722,observe the pin, it has fallen out.
Now we measure the resistance of R1722 Pin1, 450V.J1722 Pin2, 0, so R1722 is where the problem lies.
Put the motherboard onto the PCB holder.Apply some soldering paste on the bonding pad of R1722, and grab a new resistor of the same size with tweezers.
Set the hot air fun to 330℃, wind 30,heat R1722 and weld it to the motherboard.
After the motherboard cools down, measure the resistance of J1701 Pin37 again.It’s 450V,pin2’s value is 450V as well.
Take down the motherboard,install it to a new screen.Connect the display cable, the charging cable, the camera module,the earphone jack cable, the sensor cable and the battery cable.
Turn the phone around.Power on, wait for a moment,test the touching function,it works.
Problem well solved.
For further info, please check out this tutorial as below: