Generally, power issues would start at your iphone 6 plus, today I will explain how to check and repair you turned black screen iphone 6 plus. You can follow my step to try fix. If you need some cellphone repair tools, you can try vipprogrammer.com. Hoping it is helpful with you.
IPhone 6 Plus suddenly turns black under normal use and the display and touch screen power chip and main power chip have been replaced. Repeatedly turn it on and off and get into IOS test. IPhone can display only once, but it turns black in a minute.
1. According customer’s feedback, we presume that the CPU is pseudo soldering. Let us put the experience aside and measure the working condition one step by one step. The customer only sent one motherboard. We use it to connect the display screen that is going to be tested and plug adjustable power supply to turn it on. The current is above 1A, but the display screen is still blank.
2. Measure the working condition of the two ±5.7V voltages display screen circuits PP5V7_LCM_AVDDH and PN5V7_SAGE_AVDDH and find that there is no voltage. The two voltages were not produced normally generally because the working condition of display screen has not been satisfied or does not communicate normally with CPU.
3. After removing the display screen, turn iPhone on and measure the pin 35 1.8 V voltage and pin 26 I2C bus voltage of display screen socket J2019, no problem has been found. The circuit diagram of display screen socket J2019 is shown in below picture.
4. Unplug the power supply, measure the diode data of display screen socket interface and compare the data with that of a normal motherboard, finding no problem. The bitmap of display screen socket is shown in below picture.
5. After the above measurements, nothing wrong has been found. However, the two ±5.7V voltages display screen circuits PP5V7_LCM_AVDDH and PN5V7_SAGE_AVDDH are still not produced. Thus, CPU or the display and touch screen chip have something wrong. First measure the pull-down resistor R0702 of 45_LCM_REXT signal. If the pull-down resistor R0702 is damaged, the MIPI mode used to communicate between CPU and display screen will not work. The circuit diagram of R0702 and the location of R0702 in bitmap are shown in below picture.
6. One end of the pull-down resistor R0702 is connected to ground and the other is connected to pin A7 of CPU. Measure diode data of the end towards CPU is 700 and after careful observation, there is no mark of pseudo soldering. As the customer changed the display and touch power supply chip in the process of previous repair, the next testing points are lying on the display and touch power supply chip. The real material object of display and touch power supply chip is shown in below picture.
7. Teardown the display and touch power supply chip and measure the diode data to ground of display and touch power supply chip solder pad. The data is normal. Replace a tested-workable display and touch power supply chip and turn iPhone on. The white Apply logo can be shown normally, but it turns black in a few seconds.
8. Reboot it and the result is still the same. when teardown the display and touch power supply chip, the board of motherboard is heated. Does it become abnormal after it cools down?
9. Teardown the display and touch power supply chip again and blow the display and touch power supply chip by a cooling fan for 10mins. When it cools down completely, measure the diode data and we find the data still exists. However, experience tells us that if the diode data is normal, the voltage is not necessarily normal. Plug power supply and turn iPhone on. Measuring the voltage of several important signals on display and touch power supply chip solder pad, now we find something wrong. The voltage of pin C2 of display and touch power supply chip U1501 is changing constantly. Pin C2 is RESET_1V8_L which is the reset signal connected to CPU.
10. Under normal circumstances, after turning on, the voltage of the pin is a balanced 1.8V voltage rather than a changing voltage. There is only one possibility that causes the unbalanced voltage. The board of motherboard has something wrong. The location of RESET_1V8_L in bitmap is shown in below picture.
11. Reset signal RESET_1V8_L is connected to testing point TP2508 near the EEPROM, as shown in below picture.
12. Measure the voltage of the testing point TP2508 is 1.8V which is normal. Measure this point and pin C2 of display and touch power supply chip, we find that the two points are disconnects. Thus we are sure that the circuits in the board of motherboard are broken. Solder a wire from testing point TP2508 to pin C2 of display and touch power supply chip. After turning iPhone on and off many times, the display screen function is normal. Trouble is removed.