SOLVED: iPhone 6S Plus cannot turn on after expand the NAND Flash

The lack of memory on the phone is very annoying, when you want to take photos, it this time your phone will jump out the tips which about the storage space is not enough, it make you very depressed. So, replace or expand the NAND Flash of the iPhone is a god idea. However, things don't turn out the way you want, after replace the NAND Flash, the iPhone dead. So, let's fix it.

Connect adjustable DCpower supply to test and the current reached 100mA when press power button to turn it on. But 2s later, current drops to 0mA.

This problem happens after enlarging NAND Flash Storage, so we first check whether there are any explosive tin balls around CPU. Remove the shield cover and find some unobvious bumps on the upper board of CPU. Observing under microscope, there are no explosive tin balls around CPU.

Directly short connect the power supply PP3V0_NAND of NAND to ground to force it enter DFU mode. Check whether iPhone can connect to WLAN (many motherboard whose current drops will not drop any current when it enters DFU mode).

 

Plug power supply and charging connector. Use tweezers to short connect non-grounding end of capacitor C1501 at the circuits of NAND Flash power supply PP3V0_NAND to the surface of NAND (The surface of all grey chips are connected to ground), and then plug USB cable. When power supply meter shows about 700mA~1A, loosen the tweezers. If the working condition is satisfied, i4 assistance on computer will remind that it enter DFU mode. If root iPhone right now, it is certain to report error 4005. The capacitor C1501 in bitmap is shown in picture 1. The capacitor C1501 and NAND power supply PP3V0_NAND in circuit diagram  are shown in picture 2.

1

2

We enter DFU mode is just to judge whether the CPU working condition is normal and whether the lower board of CPU is normal.

When this motherboard enter DFU mode, it can connect to WLAN. According the experience, when blow NAND, the air gun blow the CPU upper board up causing the damage or pseudo soldering. Slightly heat motherboard for 1h and remove the CPU upper board (control the temperature). Then cool it and energizing it. The current now can reach 80mA. Therefore, we can be sure that it is the problem of CPU upper board. Replace the CPU upper board and iPhone can be turned on. The iPhone is coming back to life.