You can't tell from the outside, but this is a Lear Siegler ADM-3A terminal with GraFix add-on board installed. It also has a numeric keypad adapter cable that appears to have been cut off. The terminal has the typical screen rot bubbles of an ADM 3. .Click image for larger view.
Note the cables connecting from the main board to the GraFix board installed underneath. Click image for larger view.
I assume these mods are for the GraFix board, but they could also be related to the external number pad. Need to find out. Click image for larger view.
The terminal powers up and displays a cursor at the bottom of the screen, but does not reply to keystrokes in line or local mode. I have only taken a peek at the GraFix board from the side.