Well, these sets know how to bamboozle one. A UA557100AM that works perfectly one day, then goes into a continuous boot loop the next. Even with main disconnected, the reboot continued and the backlights didn't automatically come on, so i thought power supply fault. With each reboot I could see a glimmer of light in each corner.
Could it be the edge-lit strips? So I stripped the panel only to find that the LED tester lit up all LEDs in the many sectors of the strips, but running the TV only caused about 10 LEDs in each corner to function. All honky-dory. So it's back to the power supply where I've resoldered most joints, checked as much as I could and went over it with a magnifier. Drew a complete blank.
So now to hunt down another PSU, as they're NLA ex mfr.
Bruce.