As has been discussed on this board, the "Trouble with Tribbles" diagram actually is from "Space Seed." It was originally made for the script direction of Scene 44 where Khan is reviewing diagrams for a Constitution Class Starship." The close-up of the graphic ended up on the cutting room floor, but the drawing was dusted off and repurposed later for "Tribbles."
Are you sure about that, Greg? I bow to your expertise in this area, but I seem to recall reading that the two displays were not in fact the same. And that clip I posted a link to above would seem to confirm that. It doesn't appear to be the phaser schematic.