Epson Equity 286 PLUS - Manual (Page 124)

There are four corresponding tabs on the inside back panel
of the computer which fit into the openings in the
subassembly slots.
Lift up the subassembly from your work surface and lower
the back end into the computer, guiding the top slots on the
subassembly into the top tabs on the computer, as shown in
the next illustration.
5-34 Installing and Removing Options