We got an iPhone 6 to repair, the customer describes the faulty is that it is failed to flash. But the customer did not provide more details, such as what error code does it report, so we need to check it first.
Connect iPhone to computer with USB cable, and flash it, the result is that white Apple logo appear and remain motionless, and there is rotated gear shape icon appears under the white Apple logo, as shown in picture 8-5-1.
This problem is generally caused by peripherals or UART bus. Carefully disassemble cellphone by phone opening tools, and take out the iPhone motherboard. First remove all peripherals, and then flash iPhone, but the problem is still the same. Then we teardown the chips, and use multimeter to measure the UART bus, the data is normal.
Because the UART bus is connected to the A8 CPU, the data of UART bus is normal, so we only can replace the U2201 IC. After replacing the chip, a new failure occurred when we flashing iPhone 6, the iTunes reports unknown error (40).
The unknown error code 40 mostly caused by iPhone NAND flash failure. Teardown the NAND flash with rework station, we can found that the customer has removed it, and solder the green UV oil on it. Install the NAND flash and continue to flash iPhone, the progress line can move normally.
Finally, the iPhone 6 successfully finish flash. After activation, this iPhone repair completed.
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