Malfunction Phenomenon
The phone turns on normally, but the touchscreen unresponsive.
Trouble Shooting
For the iPhone X Touch Issue. First, we need to take apart the phone and run the cosmetic inspection of the motherboard first, to see if there are any components missing, corrosive, etc.
After checking the cosmetics, if everything is OK. Then measure the diode value of the touch connector J5800 of the motherboard, the measured diode value of pin 6 is 0.003, which is abnormal.
From the bitmap and circuit block diagram, we can see that pin 6 of J5800 is connected with C5802 and FL5802.
So we can check it with the rosin detecting method. Finally, we found the rosin on the C5802 gets melted immediately when connected with the DC power supply.
So we confirm that the fault is related to C5802.
Remove the filter type capacitor directly, and test. Touch function back to normal. Then assemble the two layers of the motherboard, the issue resolved.
