I've been trying to repair an iPhone 4S for a friend, but can't get it to play ball. It almost fully succeeds (75%) to reinstall iOS, however iTunes then says Unknown Error (-1). I have read online that this could mean a hardware failure, but since the phone is able to get 75% of the way reinstalled, and it looks fine inside, surely nothing too serious has occurred. I don't care if I have to reinstall officially or via special software or jailbreak, as long as I can get this phone running again. Also, after iTunes displays the error, the phone just sits at the 75% mark on the installation screen (Apple logo with bar underneath).
Thanks for any help.
Best Answer
I'd try putting the phone in DFU mode (Device Firmware Update). It's a method of last resort, but it's worth a try since it's not working now.
http://m.imore.com/how-to-iphone-ipad-dfu-mode