Solved: iPhone 6s no display fault (C4002 damaged)

A customer sent us an iPhone 6S to repair, the fault is that the iPhone 6S no display, it just shows black screen.  After we received the iPhone 6s, we start to repair.

Disassemble the iPhone, use DC power supply to provide power on it to detect it, the current is very normal. Even if the current it normal, but the iPhone screen still doesn't display. Observe it more carefully; we can see the faint light from the side, which means that this is faulty iPhone with a light but no display.

According our experience, most of the fault points in this situation are in the display touch power supply circuit. Open the power side; we can see the iPhone PCB board is very dirty, especially in the display touch power supply tube. And after check it, we can know that this display touch power supply tube has been replaced many times.

Now we're going to use Fluke 15B+ Digital Multimeter to measure positive and negative 5.7V on the iPhone display touch power supply tube, the voltage measured is less than 2V. Next to measure the voltage of boost capacitor, the voltage only is less than 2V. Now we know the boost circuit is a problem.

Because the display touch power supply tube has been replaced on iPhone 6S, so we don't need to replace it now, the emphasis is on boosting inductance and capacitance. After measuring the inductance, we found that it was no problem. Then the problem is centered on the capacitor.

Open WUXINJI Dongle to check iPhone schematic diagram, we know this boost capacitance is C4002, we decided to replace the capacitor. With the help of QUICK 861DW, we replace it smoothly and quickly.

Assemble the iPhone to test, the screen displays normally now. Continue to test other functions, all is fine, the fault has been solved. The fault is on this small capacitor.