The iPhone 6 has been drooped and the front
cover glass has broken. The touch function is lost even after replacing a fine LCD screen. What happened to this iPhone 6?
Firstly, replace the old screen with a fine
LCD screen and test. The touch function cannot be used, which suggests the
problem existing on motherboard. Take out
motherboard and check, as shown in picture 1-1.
1-1
Secondly, as the touch function is lost, we
check the touch circuit directly. Using multimeter to
measure the diode data of communication coupled capacitor between touch process
chip and touch control chip, finding no
problem. The coupled capacitor’s location is shown in picture 1-2.
1-2
When measuring I2C chip bus, find the diode
data of TOUCH_I2C_SCL is several tens. The normal one should be over 300 and
the clock should be the same as data. Generally, the low diode data is caused
by short circuit. The main chip of this signal is only the touch chip. The circuit diagram of I2C chip bus of touch chip is shown in picture 1-3 and its measuring points
in bitmap is shown in picture 1-4.
1-3
1-4
According to the experience, the damage of
touch process chip will cause the failed usage of touch function in addition to
the short circuit. Thus, we decide to remove the touch process chip, as shown
in picture 1-5.
1-5
Finally, remove the touch process chip, the
diode data of the two bus circuits of I2C chip are the same, which becomes
normal. We know the touch process chip is damaged now. Replace the touch
process chip and the touch screen of iPhone 6 was back to normal.
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