They did a revision to the sound Roms not the eprom stern has a service bulletin on how to check if you have the latest one my bet is yours is not up to date causing.this problem

I am going to be a little vague as it's been a but the out of date issue is like your phone getting a new firm wear I think the LED currently flashes 4 times and when upgraded will go to 8 but it's not the sound EPROM traditionally changed

http://www.sternpinball.com/upload/downloads/sb157.pdf

I realize your game is not mentioned but using an older sega board sort of said hey I Remember seeing this before

Plenty of people can burn that for you a wtb eprom post. can get it for about $10.00. Also I used to purchase EPROMs from ebay.com link: STERN MONOPOLY pinball eprom rom upgrade set
send her a pm and she will burn anything you want really fast shipping. The link is not for the roms you want just send a description of what your looking for. Also the board repair person should be able to do this EPROM for you it's inexpensive if you have a burner and easy.