I've added several layers of randomness, so I'm not sure what the odds of winning actually are. I just know they're low.
There are 3 slots, and each one will change if you press the button to spin. If it's spinning, the light is on.
Each slot has 4 possible options: blank (glass), gold, iron, or diamond. If all 3 match, you win the respective jackpot. The slots are obviously piston feed-tapes. Each piston feed tape moves randomly, and there is a 1/9 chance that your spin will end at any given moment.
The brains of the machine are actually these smaller piston feed-tapes up top, which all 3 have cauldrons inside them so that 1/3 full correlates to an iron block, 2/3 full correlates to gold blocks, and the full cauldron correlates to the diamond block. If all 3 match, which I detect using orange redcoders and the grey, white, and black AND gates, you get an output, which is the brown circuit.
This machine could definitely look nicer. The brown circuit can go to whatever you want (mine looks ugly since I made it go back to front), and the purple circuit (which controls the lamp) will just go wherever you want the lamp to go.