I'd try JWJs suggestion.
Boot the game and get into sound test and let it run.
Remove the ribbon connection that goes from the sound board to the dot controller at the dot controller. Any change?
Next remove the 2nd connector from the four position ribbon at the FlipTronics board. Any change?
This can be done with the game on, generally. If you hear anything lock on, power down.
The display will not work, as you've removed its data source. No biggie.
If these tests don't yield anything, my next suspicion is the sound board RAM. I've seen only one failed sound board RAM, but the results were similar to yours. That RAM isn't tested by the boot diagnostics.
It's not socketed, so use the diode test, comparing between your TAF and Creech boards, looking for differences. You'd like to be more sure before attempting repair or sending the board out. If you haven't acquired good PCB repair skills, send it out. Those boards are pricey and you don't want to hack it. While it's out, replace all the 47uf caps on the board. They are generally dried out and not doing there job.
Chris Hibler - CARGPB #31
http://www.PinWiki.com - The new place for pinball repair info