The issue isn't sammobile. It is just that att never realeased a full firmware file beyond 4.1.1. All updates were pushed to i747 owners via Ota updates.
Installing custom ROMs will require a custom recovery. That being said, try this:
download Odin 3.07: https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CBwQFjAAahUKEwiE_-vg54nJAhVGVh4KHdhyAUQ&url=http%3A%2F%2F...
The purpose of my post was to clarify the items that make up a phone display. When searching eBay, a person can purchase the digitizer, lcd, and frame as separate pieces. I have done so in the past and have replaced 3 digitizers because the LCD wa...
dawgdoc is correct about everything said.
It is not Knox that prevents downgrading from 4.3 to an earlier version, it is the code in the bootloader itself.