IBM PCjr Manual page 232

Press each button on your Joystick,
one at a time.
Each block on the top of your screen
gets smaller, as if it has been pressed.
The inside each box can be
moved by moving the control stick.
Move each to the top of its box
and around the inside of its box.
Did your Joysticks work correctly?
YES - Press I I then press
^ and go to Step 4.
3^.
NO- Have your IBM PCyr and
your Joysticks serviced.
See "Service Information"
in this section.
6-90 Attachable Joystick Test