IBM PCjr Manual page 226

6-84 Light Pen Test
Do the shapes of the blocks and lines
on your screen match the figure
helow?
YES - You are ready to test your
light pen. Press the light
pen onto the surface of
your screen anjrwhere in
the large block and go to
Step 2.
NO - Have your IBM PCyr
serviced. See "Service
Information" in this
section.