I've had seemingly random problems (though consistent in symptoms) on both my Xenon & Centaur, both were caused by shorts, Centaur from a wire stripped of insulation shorting on the chamber drop target casing, Xenon by a short from a broken off wire in the coin door, this problem tended to appear and disappear on opening/closing door, I'd check the wiring carefully for bare or loose wires. The Centaur problems particularly seemed weird and disconnected but were solved permanently when I insulated the bare wire.