Hey there Ben3362,
It sounds like you are attempting to restore your iPhone 6s Plus through iTunes and are unable to complete the restore due to receiving error 51. You've done some great troubleshooting steps thus far, which is awesome.
To begin, let's ensure you've completed all the steps listed in this article:
If you see an error when you update or restore your iPhone, iPad, or iPod - Apple Support
https://support.apple.com/en-us/HT201210
If those items don't resolve the restore error, there are a few more helpful suggestions found here:
Get help with iOS update and restore errors - Apple Support
https://support.apple.com/en-us/HT204770
Specifically, I'd take a look at the section below. Even though it lists error 53, the specific troubleshooting would still be relevant:
If you see error 53, learn what to do. If you see one of the errors below, you might have a hardware issue:
- 1, 3, 10, 11, 12, 13, 14, 16
- 20, 21, 23, 26, 27, 28, 29, 34, 35, 36, 37, 40, 56
- 1002, 1004, 1011, 1012, 1014, 1667 1669
Here's what to check:
- Make sure that you have the latest version of iTunes.
- Check for issues with third-party security software.
- Make sure that your USB cable, computer, and network are reliable. Then try twice more to restore your iPhone, iPad, or iPod.
- If you still see the error message, you can check for outdated or modified software or contact Apple Support.
As an additional isolation step, if you have access to another computer with iTunes, you can try to restore your device using that computer. This can also be accomplished by visiting an Apple Retail Store or an Apple Authorized Service Provider. If you want to visit an Apple Store, do be sure to book an appointment. Here's a link to help you find nearby service locations: https://locate.apple.com/country
Best of luck to you and have a great rest of your day!
