In today’s guide, we are going to show you how to solve the iPhone touch screen not working caused by different faults. Solving these problems is quite simple and straightforward.This guide offers you a very detailed logic board repair solution to deal with the problems that iPhone touch screen not working. Let’s dive right in:
Example of iPhone Touch Screen Not Working Problem 1:
iPhone 6 was broken and touching function was not working after replacing the screen.
iPhone Touch Screen Not Working Failure Phenomenon 1:
The iphone6 had fallen and the screen was creaked. The customer said that the touching function was still not working even after replacing with a good LCD screen.
iPhone Touch Screen Not Working Maintenance Procedures 1:
First we had to repeat the fault by removing the original screen and replacing with a good LCD screen then testing. It was true that the touch able to used, which indicated that it was caused by the mother board. So we had to take out the mother board and repair it. The defective mother board is shown in Pic 3-21.
The defective mother board Pic 3-21
Since the touch was unable to use, then we could directly check the touch circuit. Measuring the ground impedance values of the communication coupling capacitor between the touch processing chipset and touch control chipset, everything is fine. The position of the coupling capacitor on the bitmap is shown in Pic 3-22
The position of the coupling capacitor on the bitmap Pic 3-22
It was found that the ground impedance values of the TOUCH_I2C_SCL is under 100 when we were measuring the I2C bus of touch chipset, while the normal value should be around 300. Moreover, the clock and data value should be the same. Normally the low ground impedance values was caused by the short circuit. The main chipset of this signal was only the touch chipset. The circuit of touch chipset’s I2C bus is shown in the Pic 3-23. The measuring point of touch chipset’s I2C bus is shown in the Pic 3-24.
The circuit of touch chipset’s I2C bus Pic 3-23
The position of touch chipset’s I2C bus in the bitmap Pic 3-24
Based on our previous experiences, generally, the cause of touch unable to use was mostly from the damage of the touch processing chipset. Plus, the I2C bus had short circuit in this board, so we decided to remove the touch processing chipset. As shown in the Pic 3-25.
The removed touch processing chipset Pic 3-25
After removing the touch processing chipset, we needed to measure the ground impedance values of the 2 bus of I2C and the values of both signal lines were the same all in the normal range, from which we could conclude that the touch processing chipset was damaged. After directly replacing the touch processing chipset, the problem was solved.
Example of iPhone Touch Screen Not Working Problem 2:
iPhone 6 Plus screen sliding no response and the touch function no working
iPhone Touch Screen Not Working Failure Phenomenon 2:
Power on entering into the activation interface, there was no response on screen sliding and the touch function was not working. The phone was failed to activate.
iPhone Touch Screen Not Working Maintenance Procedures 2:
Taking out the mother board and it was found that there were the traces of welding on the hard disk. As shown in Pic 3-26.
The hard disk 3-26
We had repaired a lot of touch failure iPhone 6 Plus, which basically were caused by the M1’s pin broken of touch processing, judging by previous experiences. The position of M1 on the bitmap is shown in Pic 3-27.
The position of M1 on the bitmap Pic 3-27
The M1 pin signal of the touch processing chipset is called LCM_TO_AP_HIFA_BSYNC. The position of touch processing chipset’s M1 pin on circuit diagram is shown in Pic 3-28.
The position of touch processing chipset’s M1 pin on circuit diagram Pic 3-28
If the LCD display and touch processing chipset could not communicate with each other synchronously, then the touch screen certainly could be unable to use. After filling the soldering point of touch processing chipset’s M1 pin, we needed to weld the touch processing point and then power on. The touch screen could be used as normal. After activating, entering into the system to have the test, there was a blurred screen. Turning off the phone and then power on again, when the processing bar appeared, the phone crashed. As shown in Pic 3-29.
The phone crashed when power on with the processing bar appeared Pic 3-29
This kind of the fault were normally caused by a hard disk or a CPU problem. Since hard disk of this phone was welded so it was very likely to be the failure of hard disk. So we choose to reset hard disk to eliminate the possilbity of hard disk missing welded. Turning on the phone after the hard disk reset, there fault still existed. At last, we replaced the hard disk and had the phone recovery, then everything was back to normal. The replaced defective hard disk is shown in Pic 3-30.
The defective hard disk is Pic 3-30
Example of iPhone Touch Screen Not Working Problem 3:
iPhone 6 Plus touch screen sometimes not working with white stripes.
iPhone Touch Screen Not Working Failure Phenomenon 3:
iPhone 6 Plus had fallen before and it’s touch screen unusable sometimes with vertical white stripe on the top of the screen.
iPhone Touch Screen Not Working Maintenance Procedures 3:
It was a common disease of the iPhone6Plus model that the touch screen sometime could be used while sometimes not with vertical white stripe on the top of the screen. It was very easy to occur for iPhone 6 Plus that had fallen. As shown in Pic 3-31.
The failure phenomenon of iPhone 6 Plus Pic 3-31
The reason caused this fault was that the M1 pin’s soldering point of touch processing chipset was seems broken. The M1 pin was used for synchronous signal communication between the LCD screen and the touch processing chip, and the touch was ineffective when the synchronization is not normal. So we needed to remove the touch processing chipset U2402, and we noticed that the soldering point of M1 pin was teared down together with the chipset when we were the chipset was disassembled. As shown in the Pic 3-32.
The mother board after removing the touch processing chipset Pic 3-32
It was much easier to repair it, after we confirmed the failure. We just had to weld a wire to soldering point. As shown in Pic 3-33.
The touch processing chipset with welding finished Pic 3-33
After the welding point is filled with the wire, the touch processing chip U2402 is welded well, the starting test is normal and the mobile phone is repaired. After the welding point filled with the wire, we could soldering the touch processing chipset U2402. Boot test and the touch was working as normal. This problem solved.
Example of iPhone Touch Screen Not Working Problem 4:
iPhone 6S touch screen not working any more after cell phone dropped into water
iPhone Touch Screen Not Working Failure Phenomenon 4:
iPhone 6S touch screen not working any more after cell phone dropped into water, and the display touch base has been replaced already.
iPhone Touch Screen Not Working Maintenance Procedures 4:
There are big difference between touch circuit of iPhone 6 and iPhone 6S, and the touch chip of iPhone 6S is integrated into the screen display digitizer, moreover, the display and touch of iPhone 6s share same connecting seat. The display of the iPhone 6S is shown in pic 1-1.
iPhone 6S’s touch display connection seat Pic 1-1
AS the display and touch ICs are integrated into screen display digitizer, the motherboard only provides power supply, clock, reset, INT signal interruption and SPI bus communication to the touch circuit. When the iPhone 6S touch screen not working, as long as you can turn on the display, you won’t need to measure PN5V7_LCM_MESON_AVDDN, PP5V7_MESON_AVDDH and PP5V7_LCM_AVDDH, because touch and display also share these functions. The circuit of required voltage of touch and display is shown in pic 1-2.
It is generally required to measure the ground impedance value of the J4200, as well as the voltage of PP5V1_TOUCH_VDDH and PP1V8 when screen display assembled. The location of the measuring points is shown in yellow in pic 1-3. After testing, we find that the ground impedance value and voltage are normal. Then we changed a new screen display and assemble it for testing, the touch screen is still not working.
Since the iPhone 6S has a 3D Touch feature, the touch screen not working may also caused by the 3D Touch functioned abnormally. The 3D Touch is connected to the fingerprint connecting seat, after measuring the ground impedance value of finger print connecting seat, it is found that AP_TO_TOUCH_RESET_L signal is a little bit lower than normal at only 80, and normal value should be about 400. Then let’s check the bitmap and find that the reset signal of AP_TO_TOUCH_RESET_L is connected to the display touch connection, as shown in the yellow point in pic 1-4. Moreover, the ground impedance value of the AP_TO_TOUCH_RESET_CONN_L on J4200 is normal.
Required Voltage Circuit Diagram of Touch and Display Pic 1-2
Touch Display Seat Testing Position Diagram Pic 1-3
AP_TO_TOUCH_RESET_L Connection Diagram Pic 1-4
The measurement shows the AP_TO_TOUCH_RESET_CONN_L on the touch base and the AP_TO_TOUCH_RESET_CONN_L on the fingerprint base are disconnected. Remove the black glue on the edge of the fingerprint and find that FL4134 and C4134 and several elements on the side are all corroded. After replacing the the corrosion components, the touch screen and the 3D Touch function are back to normal during testing. The position of the corroded elements in the bitmap is shown in pic 1-5.
The Position of The Corrosion Elements in The Bitmap Pic 1-5
Example of iPhone Touch Screen Not Working Problem 5:
iPhone 5 touch function unable to use and after replacing the touch panel the fault still existing
iPhone Touch Screen Not Working Failure Phenomenon 5:
The touch function was unable to work.
iPhone Touch Screen Not Working Maintenance Procedures 5:
Power on and test the phone, the fault was exactly the same as the customer described. After disassembling the phone, we tested the phone with a good LCD screen to see if the fault was caused by the LCD screen or not. The fault still existed with the good LCD screen, which indicated that the problem was not from the screen instead it was caused by the mother board.
Measuring the ground impedance values of the connector of mother board touch screen by multimeter, and every thing was fine. The position of the connector on mother board touch screen is shown as Pic 3-1.
The position of the connector on mother board touch screen Pic 3-1
Then we measured the power supply on each circuit of touch control chipset U12 and touch processing chipset U14. The voltage of PP1V8_GRAPE, PP5V1_GRAPE_VDDH was normal. The circuit diagram of these 2 voltages is shown in Pic 3-2.
The touch control chipset U12 power supply circuit diagram Pic3-2
We also measured the power supply of PP5V7_SAGE_AVDDH, PN5V7_SAGE_AVDDN, which were also in the normal range. The circuit diagram of them is shown in Pic 3-3.
The touch processing chipset U14 power supply circuit diagram Pic3-3
The position of touch control chipset and touch processing chipset on the mother board is shown on Pic 3-4.
The position of touch control chipset and touch processing chipset on the mother board Pic 3-4
The power supply on each circuit of the touch chipset was all normal, so the problem was very likely to be caused by the damage of the touch processing chipset. Then we directly replaced the touch processing chipset. As shown in Pic 3-5.
The new & defective touch processing chipset Pic 3-5
After replacing the touch processing chipset, we assembled it to have a test again, and the touch function was working as normal. Therefore, the failure of touch function was caused by the damage of touch processing chipset.