Power on iPhone 6 and test it, the touch screen has no response and there is no white stripes. In this situation, the generally black touch IC does not work or CPU can’t recognize the touch IC. According the trouble phenomenon there could be disconnect. After disassemble the iPhone 6, we can find that the iPhone has been repaired, and it’s more serious. As shown in picture 4-1-2 and 4-1-3.
First use digital oscilloscope to measure touch IC, it shows 5.1V, 5.7V, and also has the voltage of black touch ic. This result indicates that both the white and black touch IC all is working, probably it’s a sync signal problem, check it with schematic diagram. As shown in picture 4-1-4, 4-1-5, 4-1-6 and 4-1-7.
From display interface to backlight test point and CPU , and then to black touch ic and synchronous circuit, on this line, as long as there is a bad chip, it will lead to no sync signal. After measure the chips, we find that from the backlight IC to U2403 was disconnected, put it under the microscope, and then we directly solder jump wire. As shown in picture 4-1-8 and 4-1-9,
After solder jump wire, assemble the iPhone 6 and power on, and then test it, touch function has been restored, as shown in picture 4-1-10. The trouble has been solved.