How to fix an unknown error occurred (1600) − iPhone, iPad, iPod touch (Nothing else worked)

If restoring your device using another USB cable worked, this means that your USB cable was defective. As fixing it is next to impossible, the best course of action is to replace it with a new one.

Note: Make sure to buy a new USB cable from authorized Apple resellers, as fake USB cables can be responsible for a wide range of issues, too.

If you tried all the other options to fix this issue, including plugging in your device to another computer, even with a different USB cable, but nothing worked, consider taking your device to a repair shop so that they can investigate this issue further and address it.

Consider restoring your device from DFU (Device Firmware Update) mode as a last resort, as it involves data loss, and only if you are 100% sure that there is nothing wrong with the USB cable and the computer. The procedure would be the following:

1. Put your device into DFU mode - consult this article on imore, if you are not sure how;
2. Connect your device with your computer, via the USB cable;
3. Restore your device, following the on-screen instruction on your computer.
   
   

Note: If you use a laptop, make sure to plug it in a power outlet first, as interrupting the restoration process is not advised and can be dangerous, and even damage your device.