Does the machine acknowledge the ball is ready to fire during game play? The cannon lights up when ready to fire. I'm not surprised about the fire button not working - I've had to replace the ribbon cable twice, and after about 30 games, the membrane switch dies, and you're forced to use the flippers to fire.
One of these days, I'll modify the assembly and use a cherry switch instead of a membrane switch. Someone else did that, have to search the Black Rose club to see how it was done.