The iPad 4 touch screen doesn’t work with you, because it’s screen has a some weird issues. The iPad 4 lost touch response in particular area of screen and could not be used normally and it has changed two brand new touch screen to test, but the problems are still the same. So, what’s going on? According to the experience, we can be sure that the problems happen in motherboard.
First, turn on iPad and install the ketchpad software to test. We find that a part of vertical screen touch is unresponsive to touch. Then teardown the iPad, measure the diode data of touch screen interface by multimeter and we found that one of the data cables’ diode data is infinite, as shown in picture 1-1.
Second, Opening the bitmap software, we can see that the data cable is connected with the touch screen chip and testing point TP169 at the back, as shown in picture 1-2and 1-3.
The measured diode data of test point TP160 is more than 600, as shown in picture 1-4. The data is the same as that of other cables’. Thus we conclude that there is line barrier between touch screen socket and its back.
Finally, after confirming the problems, solder a wire from touch screen socket to the test point at the back, as shown in picture 1-5 and 1-6.After the jumper wire is down, restart iPad and get into IOS test. Using ketchpad software to repeatedly test the place where the original problems happen. And everything becomes normal. IPad now is working normally. Using ketchpad software to test whether the iPad now is working normally is shown in picture 1-7.