Even though the "Fab" or fabrication number for the board shows "Rev 3" (presumably indicating that there were at least 2 revisions before it), there are 3 main after-the-fact modifications made to the board.
Specifically, the board was modified by:
- At least 1 Trace cut
- 4 Resistors added
- 5 Wire Links
While there is no date code on the circuit board itself, a review of the data codes on the integrated circuits installed shows that the ICs have late 1981 date codes. Further, the CEM3360 (which was likely one of the more expensive chips on the board, and so would not have been purchased too far in advance of its need) had a date code of 8112.
This would tend to imply that the board was not made before mid 1981, and likely closer to late 1981.
Next: Rhodes (trace cut)