Quoted from fathermystic:I unfortunately didn't have time tonight to lift the playfield and troubleshoot it.
As with any game, be sure to remove the balls before lifting the playfield. In this game, it's especially important because you can damage the subway if you don't. There is an option in the test menu (the last one, 16 I think) to remove the balls from the playfield. After selecting it, you'll have to close the coin door or manually activate the coin door switch in order for the game to release all the balls (6).