The board still works today. At least at 2MHz — it's a bit iffy at 4. I guess all those long wires don't help much. Also, I noticed that by the time it gets to the left hand side of the board the voltage has dropped from 5V to about 4.5V, so I put some wires directly across there. I also added a buzzer.

I then made the same mistake I keep making — changing more than one thing in the VHDL code at a time, and then not being able to track down where I broke everything. Fortunately I sorted everything out, and was able to send a small programme to the board to turn the buzzer on and off:

ld a, 1
out (6), a
nop  # about a hundred of them
ld a, 0
out (6), a

Yep, that's the biggest programme this computer has run so far.