Epson Apex-80 - Manual (Page 133)

Inserting the interface board
1. Locate the connector cover at the back of the upper case, shown in
Figure E-3. Push it down and in, toward the inside of the printer,
until it clicks. You need to move the cover to allow access to the
new interface connector when the case is reassembled.
Figure E-3.
connector cover
2. The screw marked CG at the rear of the circuit board is the
connection for the frame ground wire. Unscrew it and then use it to
connect the frame ground wire as shown in Figure E-4.
Figure E-4.
Connecting the frame ground wire
Choosing and Setting Up Optional Interfaces E-5