I have the Flash Baseball schematics for sale ($30USD includes postage
to US, Canadians have HST/PST tax to be added depending on their
province, International costs a bit more...), but I too am missing the
Ball Detect schematics. I have the large main one, amp, bat control, and
game over as well as the troubleshooting info on those and the parts
manual with 1970 prices.
I did sketch on the large schematic the beginning of the PC554-912
schematics at some time in the past, enough to give you a clue as to how
it works. The main suspect on these old PCBs is always the electrolytic
capacitors first (replace them if original!) and go from there.
(Please post followups or tech inquiries to the newsgroup)
John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9