Honesty thinking about it. If the light boards don't work. I'd try replacing the caps if that doesn't solve the issue it's probably a board issue. Maybe try swapping with a known good working board. Or I'd you wanna ship your light boards to me. I'd be willing to test them in my machine.

Am particularly curious whether anything is supposed to be connected to J2 on upper right of the lamp driver.

This is the only loose connector in the cab.
And tracing it back it leads to the main harness here. @brokentoken thinks it may not be used as this is a JAMMA+ cab.The loose connector on the previous pic doesn't appear have a spot on any of the boards to mate up to properly. J2 is the only unused connector but the wires don't line up right and don't want risk connecting and blowing something out lol.



