UN50J5200 only part of screen lights up then fades to dark

I have a Samsung UN50J5200AFXZA that powers up and shows just a white bar about 2” wide all the way across the top of the screen when you first turn it on, but then that bar gradually fades to black over the course of about a minute or less and the screen remains completely blank.

I’ve pulled the back and verified that the backlights are definitely working and keep working for as long as the power is on. I have measured 12V at the points where you would expect it on the power board. The main board is in the range of 3V where you would expect it. The T-CON board is in the range of 1.2V to 1.8V in the areas where it’s sending signals to the LED drivers, and I detect a range of voltages up to 1.8V along the LED drivers along the bottom of the panel. None of these checks appear to point to any of the boards having gone bad, although I become much less certain about my diagnostics the further down the signal path I travel (as voltages get smaller).

Should I just conclude I’m looking at a bad panel here? I can’t seem to locate any way to verify a bad panel other than simply process of elimination.