Normal Current While iPhone 6S No Display

Got this iPhone 6S which happens no display but normal current, we doubt the  iPhone PCB Board  may occurred something abnormal. We check it by   DC power supply, of courser, the current and voltage shows normal, but the screen still can't show normal. But during we check it, we found a faint light in the side and the pcb board is very dirty which has some solder flux, we doubt this isn't new phone. We decided to disassemble it.

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.

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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.