Update: I found out that the board is likely compatible to the HP12554. At least the corresponding diagnostic program runs without error. Also the cable edge connector matches to that of a 12554.
The only question is now, what is the meaning of the four dip switch arrays. I can only guess the function is similar to the jumpers on the 12554, but there is no obvious correspondence between these.
I would really appreciate if someone could share a manual. Otherwise I would have to reverse engineer the logic.