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.

  • Are you really stating that since the iPhone "looks fine inside" that it can't be a hardware issue? – fsb Apr 26 '17 at 17:02
  • @fsb Not at all. I'm simply stating that upon inspection, nothing blindingly obvious like a lose battery connector or a water damage sensor being triggered is visible. I just mentioned that I have had it open and have checked the obvious things. I also said that surely nothing much can be wrong as the phone does power up and start, and almost complete installation. If its alive enough to do this then nothing much can be preventing it from installing fully and booting up other than a failed check. – DevelopedLogic Apr 26 '17 at 17:40

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.


  • This didn't fix the error, but you taught me what DFU mode really is, and I now know its not the Connect To ITunes logo – DevelopedLogic Apr 26 '17 at 17:52

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