These machines typically have a min amount of money that needs to go in before it will pay out. If you want to test if the machine is ready to let you win when you play a turn and push stop for it to go in, if there is any 'lag' or delay before it stops (to make it hit the top of the key) or it stops instantly when you're too low it's not going to pay out. There are quite a few videos on Youtube showing how it works.