Are all the diodes the correct bias? Was the machine previously working properly.
Not sure how others would diagnose it but this is what I would do. Disconnect the row plug from the driver board. With a piece of wire somehow only jump the lamp row that the lamp you are testing is on from the plug to the pin on the driver board. If the second light still comes on it must be a short in the field. If not it could be on the board.
