How to fix iPhone 6P boot fault ?

Most of fault needs to disassemble, the next one can't be avoided.

The customer sent the iPhone 6P to us which along with the boot failure. Before we check it, we need to know the normal value, the data can show everything.

Disassemble the iPhone 6 motherboard and connect DC power supply while open the wuxinji diagram on the computer, there is no short circuit, then triggers we find that the current directly jump from 400mA to 1A, the main board is short circuited, now taking off the main board to observe, the iPhone 6 Nand was repaired before.

Use Fluke 15B+ Digital Multimeter to measure the power supply around NAND, it shows 1.8V short circuit, we are going to remove the NAND to observe under Trinocular Stereo Microscope. As shown in picture 15-8-1.

picture 15-8-1.

It's a little dirty on Nand chip parts. First, we reprocess the pad. There were 2 points were dropped, as shown in picture 15-8-2.

picture 15-8-2.

Measure the two points and see if there is any problem. The point is measured as ground connection (the normal point value should be infinite).

Disconnect the jumper wire soldered by the last repairman.

After processing, measure the iPhone 6 NAND CHIP, we find it's normal power supply 1.8V. Without NAND installation, we connect DC power supply to see the triggered current is 70mA, it's DFU mode when connect with computer(it happens when no NAND on motherboard or NAND doesn't match with CPU), then we remove the NAND on WL PCIE Test Fixture to see if it can be read, the result shows the NAND chip is not bad, now we re-install the NAND.

The triggered current is still 70mA, so we suspect that the NAND chip is not original, install the motherboard back and connect a computer with recovery mode, we want to check whether it can read the serial number of NAND. It can be read, so we continue to recover the data til succeed.

Unfortunately, we need to the ID identified  during the next repair process, if we unlock it, it may cause the data damage. So we have to request to our customer, we need to assemble it now. Later  we will continue this fault, thank you for your reading.