Jim asked: “My iPad mini updated to 9.3.4 and now 2/3 of the screen is dark and 1/3 of the screen is light. What happened and how do I get rid of it?”
Jim, that really sounds like a hardware problem. Maybe the update heated up the iPad enough that a faulty piece finally gave, but it doesn’t sound like it’s a software problem.
The same thing happened to a batch of iPad 3s a few years ago, half of the screen would be dimmer, in some cases it would work normally after a restart and then suddenly the problem would reappear.
You have a Mini, not an iPad 3, but it does seem to be the same kind of problem: a faulty backlight.
Your best bet is to take it into an Apple Store and have it looked at, you won’t really be able to roll back the installation and make it go back to normal, there is almost certainly a physical component at fault here.
If you’re still under warranty it shouldn’t be a problem they’ll just bring you another one and you’ll walk away with a new one, if you’re not… well, from what we’ve seen from other backlight problems, it may not even be repairable.
Take it in and see what they say, we’ll keep our fingers crossed for you, but it’s probably a hardware problem and those are rarely easy to deal with on mobile devices.