Getting the Transistor Specialties 1519 back on the bench for some overdue continued exploration.

I’ve found that I can get the ‘B’ channel to increment it’s count by toggling the gate Start/Stop switch.  It’s a center return switch, and only by running the switch all the way from Stop to Start, across the center detent, can I get it to increment.

Some further discoveries:
this toggle trick only works around 110v line voltage.  I’m running it on a vairac, limiting it to 115v.
Earlier I think remarked that it was either 3 different flavors of boards, then I realized it might only be two?  It’s three.  The first counter card is different.  Though the layout is largely the same, some components are different, and it dawned on me only now that it’s probably because that card is the one’s counter, and thus needs to have a much higher bandwidth than those following it.  duh.

Here’s the beginnings of a schematic for the input card (one of two) ignore the ‘trigger level controls’ note.