iPad Air 2 reboot issue: it shows red screen and reboot when enter IOS

Trouble phenomenon

We replace the new USB management chip on iPad Air 2, because it cannot be charged, then the charge function have become normal, but something wrong. It doesn't go into the system properly, and some times is show red screen and the auto restart.

Solution

Because we changed the USB management chip, then we worry about that the USB management chip is damaged or the solder is worse, so we replace the chip again. But the problem remains the same, this means the problem is not related to the USB management chip.

Then we unplug all the connection cable from other peripherals to motherboard to troubleshoot the problem, such as camera, sensitization, as shown in picture 7-14.

Put the single motherboard with display flex cable on electric tester. After unplugging all peripherals and testing many times, the problem remains the same, which suggests that the problem is unrelated with peripherals.

According our experience, after excluding the peripherals problems, damaged NAND FLASH and pseudo soldering could cause iPad red screen. The biggest possibility is that these two chips, CPU and NAND FLASH. We replaced the NAND Flash first, The motherboard without NAND FLASH is shown in picture 7-15. But after soldering NAND FLASH again, the problems still the same. So we re-solder CPU and test, the problem was solved, and the iPad back to normal work.