I had this and replacing the game ROM fixed it.
However, I went through everything to figure it out including full restore to factory which was suggested to me first as well as verifiying the trough and shooter lane switches were all good and the coil wasnt shorted. But like you mine always fired twice.
Mine came off route and always did this. It sounds like yours has also done this as far as your know? Can you ask the owner you bought it from if it always did it?
Its been over 10 years so I dont remember if it always did it or sometimes did it. I think it always did it so yours could be different.
One thing is I went to the home ROM 1.13 because I wasnt sure if the original 1.0 did this.
Good luck
Onekama, MI
