IBM Personal Computer AT Manual To Operations page 302

YES
NO
Press each key once. As each key is
pressed:
•
The corresponding character appears
in each block on the screen.
•
The three squares in the upper right
,.-......,
corner of the screen will intensify.
•
The three status lights on your
keyboard come on.
• Go to Step 4.
Press N and then press Enter
(~
).
Note the error and have your keyboard
serviced.
300-4 Test