All 56 UNIBUS signals are shown by diagnostic LEDs on card front. Also supply powers are routed out for easy testing.
The LEDs are of 1.8mm type, these fit in the 100mil grid. They should be mounted looking vertical out of the case, this needs a 3D printed mount:
The 3D model for the mount are attachements on this page.
When viewing onto the card front from outside the PDP-11 card cage, we see these indicators:
1. Far left power connector:
2. Left half of LEDs:
3. Right half of LEDs:
These LEDs ares not just to have a light show. Dead bus driver may cause constant "active" levels, these are visible immediately.
Also an open "GRANT" chain shows up immediately by "active" BG* signals.
The LED drivers are analogous op amps, the LEDs show the voltage level ... which may be of some use. Input impedance is very high, so an open signal input may cause irregular flicker.
Most LEDs are lit on "LOW" voltage on the bus, as this is defined as "active" or "asserted". Only BG4,5,6,7,NPG light on "High".