This goes out to all nine of you who are following my project. I'm terribly sorry for the lack of updates, which accurately reflects the lack of progress. Real life sort of gets in the way, you know how it is.
However, one notable thing happned: it occurred to me that I'm an idiot. Yeah, no, to be honest I kind of knew that already, but I've found a new way of being one. See, I swear had I the Accom keyboard working perfectly, and I had the VFD working perfectly, too. Put them together, and havoc ensued. Courtesy of a shower thought, I'm pretty sure I now know why that is, and two plans of moving forward.
The keyboard, using the ribbon cable, passes active-low signals back to the main board. The main board also holds the 18 lighted key switches, which don't go through the ribbon but directly to a bank of PAL chips (which I've lifted out in order to tie in a separate 34-pin ribbon that goes to the other box socket on my fancy red PCB).
...only, the signals to the PAL chips are active high. 🤦
I know, right? Since I'd drawn up this fancy red PCB with the dual 34-pin box sockets, apparently it never occurred to me that the signals might be incompatible. So, now, I'm thinking: do I redesign my board and "spend more pins" on separating the bus into two; do I create a little daughter board to invert the signals; or do I attempt to program the Teensy to switch pin modes from active low to active high smack in the middle of each scan?
Currently, I'm considering buying set of male/female 34-pin connectors and a couple of TI 74HCT14N logic inverters, and build a small daughter board. I don't think I want the mess of mode switching in my source code, and I definitely don't want to allocate more I/O pins as I'm not sure I even have enough to fully support the 7 rotary dials and the track ball. This final issue might have been less critical if I hadn't destroyed the solder pads of a bunch of the I/O's on the underside of the Teensy ... or if new Teensies were expected to be back in stock sooner than 10 months from now. Talk about long-term lingering effects from the Covid pandemic.