OK, just took a look at the trough and optos and made the following observations:
In the trough assembly, there are two optos and 3 microswitches.
One of the two optos records trough jambs and the other opto records trough position one.
The three microswitches record trough positions 2, 3, and 4.
So when ball three is in play (namely when my premature game-over occurred), there would have been no physical ball present in trough position 4 (while the other trough positions had physical balls closing their respective switches). There are four balls in this game.
Wondering if the above data now points to a false closure of the microswitch controlling trough position 4 (when ball 3 was on the PF)...or do you guys feel my focus should still be on the opto PCBs and their respective IDCs?
(I did observe one IDC was slightly not fully seated--in fact the pic shows how I found it. Got an IDC insertion tool and reseated all 5 wires in the connectors and reseated the connectors to the IDCs.)
Suppose the thing to do now is just play some test games--or does anything else come to mind per the above and attached pic?