Trouble phenomenon
The screw on motherboard is snapped, after fix it, then the touch function
not working.
Repair steps
1. 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.
2. Use digitaloscilloscope 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.
3. 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,
4. After solder jumpwire, 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.
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