IBM PCjr Manual page 246

Press the keys you wish to test. As
you do, the character for each key
you pressed appears at the top of the
screen.
Are all the characters for the last
keys you pressed displayed at the top
of the screen?
thelastkeysyoupressed
YES-
NO-
6-104 IBM PCjr Keyboard Test
m
Go to Step 3.
Have your IBM PCjr
serviced. See "Service
Information" in this
section.