There is nothing more frightening than your iPhone suddenly turn black. When your iPhone screen can' t work, you have nothing to do and don' t know how to fix it. If it is the hardware issue, you generally require an iPhone professional repair. Unless you are very tech savvy, have the fully phone repair tools and equipped, and willing to take the risks of getting the iPhone bricked in the process, then you can go ahead and do the repair yourself.
The problematic iPhone 6 has the fault that is cannot turn on. Need we remove the motherboard and connect it to DC power supply, at this process, we found that the process of current jump is normal, which shows that iPhone 6 is not unable to boot, but not display.
So we initial judgment of the iPhone 6 motherboard without maintenance, maybe caused by the water damaged, fall pieces and so on. we carefully check the display adapter, there is no obvious fault. And now we measure the data of display adapter (reference schematic diagram and phone repair system), the resistance data of display adapter all is normal. As shown in picture 1-1 and 1-2.
Then we use the multimeter to measure the power supply, it shows +5.7V,-5.7V, the backlight boost circuit is only about 4V. However, on the normal case, the backlight boost circuit should have a voltage of about 11-17V. As shown in picture 1-3.
At this process, because the backlight boost circuit is not normal, so we need to check the circuit and find the problem. As shown in picture 1-4, 1-5, 1-6.
The display screen working principle and analysis:
1. The machine is powered on 1.8V, through a small inductor to reach the display screen.
2. The CPU detects the display screen through the MIPI line.
3. The CPU sends the reset signal to display screen.
4. The display screen sends the power supply signal to the display screen power supply IC.
5. The CPU outputs the video signal through the MIPI line, the LCD screen can display.
At this time, we find the backlight power supply is abnormal, but the +5.7V is normal, this situation is usually caused by damaged backlight IC, damaged backlight chip peripheral components and backlight IC solder pad disconnect or virtual welding.
So we use the exclusion method to check the perimeter first, finally check the chip. We need measure whether the peripheral inductance of the backlight IC is open or not, whether the resistance has become larger, and whether the diode breakdown. However, none of this has found fault. As shown in picture 1-7 and 1-8.
Then measure the data of each pins on U1502 backlight drive IC, all is normal. As shown in picture 1-9. So we suspect the chip itself is damaged, replace the new chip.
After measure the voltage of C1503 with multimeter, it has 16V, which is the normal data. This error repair completes. As shown in picture 1-10, 1-11 and 1-12.
More information about phone repair tools and guides, you can choose Vip Fix Shop Team.