What to do when the touch screen becomes not working or the screen die for your phone or iPad? The iPhone and iPad users depend on the touchscreen most of the time, and any issue with the screen can spoil the fun. How to fix the touch screen on my iPhone or iPad is a pretty common question. We will provide you with some potential solutions to fix iPhone or iPad touch screen issues.
IPhone 6 touch function is completely lost.
1. Enter system to test, finding the touch function is completely lost. After replacing a display screen, the result is the same. Remove the motherboard and observe, finding little soldering paste around touch process chip, which suggests touch control chip and touch process chip have been welded.
2. First measure the diode data of two ends of coupling capacitor that is used to communicate between touch control chip and touch process chip. The data is normal. One end of coupling capacitor near touch control chip is connected to touch control chip, while the other end of coupling capacitor near touch process chip is connected to touch process chip.
3. Next, measure the power supply voltage of PN5V7_SAGE_AVDDH, PP5V7_SAGE_AVDDH, PP5V1_GRAPE_VDDH and PP1V8_GRAPE. The relevant circuit diagram.
4. After measuring, we find touch control chip ‘s PP5V1_GRAPE_VDDH and PP1V8_GRAPE have no voltage, which suggests there is abnormal communication between CPU and touch control chip. Generally, the damage of touch control chip or abnormal weld and the SPI bus, clock and reset between touch control chip and CPU. Measuring points are the yellow points shown in below picture.
5. After measuring, the diode data of these points is normal, so there is no problem in communication bus circuit between CPU and touch control chip. Then power on again to test the 32kHz crystal oscillator, finding no voltage. If 32kHz crystal oscillator is normal, there should be 0.9v voltage
The material object is shown in below picture.
6. The function of 32kHz crystal oscillator is to send its frequency to main power chip. Then main power chip sends its clock signal to CPU. After receiving the clock signal from main power chip, CPU sends it to touch control chip clock signal. Find the clock pin of touch control chip and measure the diode data. The data is normal. Therefore, CPU has no problem. The damage of 32kHz crystal oscillator and the faulty chips that use 32kHz clock will cause the abnormal of 32 kHz clock, especially the Wi-Fi parts.
7. Replace crystal oscillator and power chip first, finding the problem is still the same. Then remove WiFi chip and measure. Now the 32 kHz clock has 0.9v voltage. After assemble touch control chip, the touch function becomes normal. Trouble is removed.