I picked up a very nice JD to upgrade over the one I had and I noticed the planet ring had holes instead of slots. It was also running the original software. On IPDB it says: The test game version would lock balls on a ring that rotated slowly around the planet, until the third ball was locked, and then all three balls would be released by the Space Station Robotic Arm (a magnetic crane) for multi-ball.
In the production games, the locks are virtual and only the third locked ball is actually diverted to the planet, where it goes directly from the loading ramp to the crane and is lifted out immediately. The holes in the ring were cut open so if the crane ever failed, the balls will just fall off the ring as it turns.
Does anyone know of any other differences I should look for? Was someone just lazy in replacing the ring, or could it be something special? Or can anyone with the original ring call theirs a prototype?
Any answers/history would be great. Thx