Chosen Solution
I have similar problem with back light flashing about every 5 seconds. When I disconnect the cable to the main board the back light flickers very quickly.
@jmp1 when you separate the mainboard from the power board, the backlight should come on continuously. What you are describing sounds very much like a failed backlight strip. If you give us your complete model number we can probably guide you to the right replacements. Changing those is not a terribly complicated job, just tedious and a bit of a PITA depending on the size of the panel
