IBM 3270 Option Instructions page 7

4.
Move your keyboard and all external options away from
the work area.
5.
Position the system unit to allow access to the rear.
6.
Using a flat-blade screwdriver or a 1/4-inch nutdriver,
remove the cover mounting screws by turning them
counterclockwise as shown in the figure below. Save
the screws for the installation of the cover.
Cover Mounting Screws
(These three screws may not be
present on your system unit)
APA Adapter 3