This is a graphics extension hardware for Robotron KC87, Z9001 and KC85/1. Those machines normally work only in the text mode. The graphics extensions adds memory and logic to display a new graphics screen on the output monitor, by switching between internal graphics display generator and computer’s text mode display.
An anecdote says, that this module was designed and created, because in the East Germany there was a shortage of paper and it was too expensive to test programs using a real plotter, that required real paper.
To better understand the theory of operation of this module, please read the User’s Manual – an English translated version is here: robotron-grafik-zusatz-english.pdf.
A video of a working system:
To discover what chips were broken and replace them, I installed sockets for all chips. It occurred the faulty ones were a few memory chips.
This connector was another reason for failure, since some of the delicate wires needed soldering back to their traces.