Though iPhone series products had updated to iPhone X and iPhone 8/8P , their predecessor iPhone 6 still have many its users . As the time going by , Those users who bought their iPhone 6 many years ago found more and more malfunction . Today let us discuss about that why iPhone 6 touch screen becomes uncontrollable and it opens APP automatically .
Customer says that other maintenance staff has fixed his iPhone before. The touch screen becomes uncontrollable and it opens APP automatically. The screen assembly, iphone touch control chip and touch process chip have been replaced.
Power on and enter system to test, finding the trouble is the same as the customer’s description. In general, disturbance to touch chip or unstable power supply cause such problems. Use oscilloscope to measure PN5V7_SAGE, PN5V7_SAGE_AVDDH, PP5V1_GRAPE_VDDH and PP1V8_GRAPE on touch control chip and touch process chip, finding the voltage is stable, as shown in picture 3-6 and 3-7.
Picture 3-6
Picture 3-7
The real location of touch control chip U2401 and touch process chip U2402 is shown in picture 3-8.
Picture 3-8
Measure the diode data between the touch screen socket interface and touch process chip U2402, finding it is normal. The material object of touch screen socket is shown in picture 3-9.
Picture 3-9
Measure the diode data of two ends of coupling capacitors that is used to communicate between touch control chip U2401 and touch process chip U2402.
These coupling capacitors’ circuit diagram is shown in picture 3-10. The material object is shown in picture 3-11.
Picture 3-10
Picture 3-11
The working condition of touch chip is normal, but why the touch function is not normal? Does the touch process chip that the previous maintenance staff replaced not work properly?
According to the repair experience before, the problems of touch control chip will lead to the failed usage of touch function. While the problems of touch process chip will lead to partly failed usage, vertical bar of touch function. Although the later case have not been met, we still doubt about the touch process chip is abnormal. Replace the touch process chip and the problem is still the same. Exclude the abnormal working condition of touch process chip and touch process chip’s damage, leaving the only possibility of the disturbance to HF signal. The assistant NFC chip beside touch process chip is very likely to disturb it, as shown in picture 3-12. The assistant NFC chip has HF signal output. If it is damaged, it will affect the normal work of touch chips.
Picture 3-12
Remove the assistant NFC chip and power on, finding the touch function can be used normally, which we can be sure it is the assistant NFC chip that causes the problem. Replace a fine assistant NFC chip and trouble is removed.
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