System 6 and System 7 driver boards can be swapped for testing

Williams System 6 and System 7 driver boards fit each other's games, so a board from another game makes a quick test when a coil or lamp circuit is dead. The System 7 version has some switch-matrix resistors replaced by zero-ohm jumpers for faster switch response, so a System 6 board in a System 7 game can show switch-matrix oddities, but nothing is damaged.