iTunes error 40: the iPhone 5S update IOS failed

Most the owner of iPhone 5S has been meet iTunes error code, what does that mean? When you want to update the IOS system, it is failed, and shows unknown error code on iTunes. Here is example, when we update the IOS, root it and then it reports unknown error 40. What's going on? We need to fix it.

Different computer may have different circumstances when root it, this is because of computer system software and other issues. We root iPhone 5S again, we found that when the progress bar goes about one tenth, as shown in picture 7-16, it reports error 40.

As our experience, when the progress bar goes about one tenth, it reports error 40, which may be related to NAND FLASH. Next, remove motherboard and pry up NAND FLASH, as shown in picture 7-17.

Then, use JC NAND FLASH Test Fixture to test NAND FLASH, finding no series number in NAND FLASH, as shown in picture 7-18. Thus we know that the NAND FLASH was damaged.

Next, we need to replace the new NAND flash, as the series number is stored inside NAND FLASH, at the same time; we have to replace the series number too. Because the original NAND FLASH is damaged, I cannot know the series number from original NAND FLASH, so I have to search the series number through original motherboard IMEI.

Finally, after writing the series number, we root again and the rooting goes smoothly. The IOS of iPhone 5S can be update restore now.

Note:

The method of getting motherboard IMEI without touch any chips:

Remove a NAND FLASH from a workable motherboard and assemble it on the faulty motherboard to root. When the activation interface is shown, clicking the icon that resembles exclamation mark, we can see the IMEI. Now I can search the series number through original motherboard IMEI and write series number into the workable NAND FLASH, the operation interface is shown in picture 7-19.