Trying to fix my brothers UN70NU6900FXZA YA02 with the same issues. Tried swapping the mainboard, no luck. I get the startup sound with old board, or replacement board, but have never been successful getting the picture back after re-connecting the ribbon cables. About to dive into the wire jumper trick and/or replacing the resistor. I wonder if my replacement board is not "new". Maybe has the same issue as the original.... Seems like one of them would work unless the problem lies elsewhere.