Rick is absolutely right! The pay-off odds are on a computer chip, installed at the factory! They cannot be reset, on the ship, without all sorts of equipment, etc; that they just don't carry aboard.
Because the pay-offs are random, they can come in "spurts," and it looks like the machine loosened up. However, over a period of time, the house will make it's percentage of play, and some will have won and some lost.