I just came across an identical problem like You have. The second button from the right, ( MAX BET ) works but It doesn’t light up. When i went to go try replacing the bulb, I noticed that the wires with the terminals on the end came out of the socket with the bulb. I tried reseating them and ended up putting a new button/ bulb in it. Works fine now. Looking at it closer I found one of the wires for the bulb was connected to the terminal, but ONLY by the insulation. The wire is broken and it can’t be seen by the naked eye.