Someone had already replaced and socketed i3 (a 6116 type ram) and this made no difference to the error.
Checking the very nice schematics there was pretty much only one thing that could be the issue.
The 051960 konami custom chip. I had one left in my little box of customs, in unknown working condition. It came from a Main Event board that I'll be harvesting for more parts later in the repair.
Anyway back to the 051960
Replacement custom in place.
Yay the ASIC is good.
This just left the sound section, four capacitors were broken off the board.
The electrolytics I have plenty of but I didn't have the correct value for the mylars so I dug out the scrap Main Events board and pulled two from that.
Sound fully restored, repair complete.