LG TV does not power on

[mzeitlin3348]

I have a LG 65UK6090PUA television which no longer turns on. It worked flawlessly (covered outdoors) for years until today.
When I use the remote to turn it on, the TV displays a red LED at the bottom of the screen which blinks 3 times then stops.

Anyone have a similar LG TV and fixed this problem? I read it is likely the power supply board or it could be the LED backlight or even the main board.

The power supply board replacement is about $40 and would be worth doing if that is what is most likely the cause.