Follow this guide to repair iPhone 6 plus display problems. This guide offers you a very detailed logic board repair solution of the problems which there is no display suddenly of iPhone 6 Plus in normal use and the right side of iPhone 6 Plus screen was off while the left side could display normally.If you want to learn more about iPhone touch screen logic board repairing guide, follow the more comprehensive version that covered most of the iPhone model HERE.
Failure Phenomenon 1:
There was no display suddenly of iPhone 6 Plus in normal use and the chipset of touch power and main power was replaced. Then we tried to power on and power off repeatedly and only one time can start to display, about 1min later the screen off again.
Maintenance Processes:
Based on the customer’s description, we guessed the fault might cause by the missing weld of CPU. Well, this was just judged by experiences, we still had to test all the working condition step by step on repairing. We only received a single motherboard from the customer and we connected it with the testing LCD screen and plugged in the adjustable power supply. The current was above 1A but the screen was still off.
The circuit working condition on the measurement showed that there was no voltage on circuit PP5V7_LCM_AVDDH and PN5V7_SAGE_AVDDN , which was supposed to be±5.7V. The fault of 2 voltages not produced was normally caused by the screen working condition unsatisfied or the communication with CPU is not normal.
After disassembling the LCD screen, then we had to power on and measure the pin 35’s voltage of LCD screen connector J2019, which was 1.8V. There was no problem found on the voltage of pin 24 and pin 26’s I2C bus. The circuit diagram of the screen connector J2019 is shown in Pic 1-1.
The circuit diagram of the screen connector J2019 Pic 1-1
After the power was pulled out, we measured the ground impedance values of the connector, and compared with this value of normal motherboard. Everything was normal. The bitmap of screen connector is shown in Pic 1-2.
The bitmap of screen connector Pic 1-2
After all the above measurement, no problems were found, while the±5.7V was still not generated. So it was very likely that there was something wrong with the CPU or display touch power chipset. First,we measured the pulldown resistance RO702 of the 45 LCM REXT signal, and if there was something wrong with resistance then the CPU and LCD screen ‘s MIPI mode would not work. The circuit diagram of R0702 is shown in Pic 1-3. The position of R0702 in the bitmap is shown in Pic 1-4.
The circuit diagram of R0702 Pic 1-3
The position of R0702 in bitmap Pic 1-4
Connecting one end of the resistance to the ground and the other end to CPU’s pin A7, by measurement the ground impedance values of the CPU end was around 700. There was no trace of missing weld on R0702 after the careful observation. Since the customer had replaced the display touch power chipset before, so we would focus on the troubleshooting of display touch power chipset. The position of display touch power chipset on the motherboard is shown in Pic 1-5.
The position of display touch power chipset on the motherboard Pic 1-5
After removing the touch power chipset, the ground impedance values of the pad of touch power chipset were showed in the normal range. Then we replaced with a good touch power chipset and booted test again. The phone could be powered on with the white screen, but after few seconds the screen was off again. Starting up again after power off, the screen was still off. Is it possible that the main plate layer was heated when we removed the touch power chipset? Then after the motherboard cooling down, it was unable to work normally.
We removed the touch power chipset again and used the cooling fan to blow the motherboard touch power chipset for 10 min. After the complete cooling, we re-measured the ground impedance values and it was found that there was a value for it. But based on the repairing experiences, even the ground impedance is normal, the voltage is not necessarily normal. We plugged in the power immediately and started up the phone, and then we measured the voltage of a few important signals on the touch power chipset pad. We found the abnormal that the voltage of C2 pin of touch power chipset was hopping continuously. C2 pin is RESET_1V8_L, which is the reset signal connected to CPU. The C2 pin of a normal motherboard from a good phone should be a stable with 1.8V instead of a hopping voltage. There was only one possibility that there was something wrong with the motherboard plate layer. The position of RESET_1V8_L in the bitmap is shown on Pic1-6.
The position of RESET_1V8_L in the bitmap Pic 1-6
The reset signal of display touch power chipset’s C2 pin also connected to the TP2508 next to the hard disk. As shown in Pic 1-7.
The TP2508 test point on the bitmap Pic 1-7
By measurement, the voltage of the TP2508 test point next to the hard disk was in normal range 1.8V but this test point was not connected to the touch power chipset’s C2 pin, from which we were sure that the circuit of plate layer was broken. So we needed to solder a connection line directly from the TP2508 test point to the C2 pin of touch power chipset's pad. After that, we booted test many times and the screen could display as normal. This problem solved.
Failure Phenomenon 2:
After the power on, the right side of iPhone 6 Plus screen was off with black color, while the left side could display normally. After the screen off, it was unable to display again when activated.
Maintenance Procedures:
This kind of screen fault was caused by the backlight circuit problem. First, we had to repair from the backlight circuit. After the motherboard was disassembled, we noticed that the right side of the backlight was coated with green oil and a line was welded on it, which was from the A1 pin of backlight chipset U1580 to the yellow test point of fingerprint connector J2118. As shown in Pic 2-1.
The position of the flying line connecting on the bitmap Pic 2-1
The I2C bus of the left side backlight chipset U1502 and the right side chipset U1508 was not the same one. The left side is normal while the right side is not, even after the chipset was replaced. So we doubt that there was something wrong with the I2C bus on the right side of backlight chipset U1508. The 2 backlight chipsets on the motherboard are shown in Pic 2-2.
The 2 backlight chipsets on the motherboard Pic 2-2
Checking the stub under the microscope, it was found that on both sides of the left and right the screw whole was twisted off. As shown in Pic 2-3.
The screw whole was twisted off Pic 2-3
We scraped the left screw hole with the blade and did not find the broken line while we found the broken line on the right screw hole. As shown in Pic 2-4.
The broken line on the right screw hole Pic 2-4
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