Why Toshiba 65ul2163dbc 65 " dim

@olio4336 nope! DO not buy a board! Don't waste your money :-) This "If i shine a torch in the display you can make out the toshiba logo on powerup" is pretty indicative that you have a bad backlight. You will need to have to replace the backlight strips. It's a PITA but not impossible to do. Just make sure you have a couple of hands available to remove the LCD so as not to flex it. Check something like this video Same idea, different model.

If in doubt or if you need further help with that, post some images so we can try and guide you remotely. Adding images to an existing question