IBM 5280 User's Setup Manual page 112

5.
Locate keyboard 0 and observe this display.
It may take a few seconds for this display to appear.
THIS IS YOUR 5280 VERIFICATION PROGRAM.
Press
ENTER
to continue.
Note: While running the verification procedure, you will notice some noises
from the diskette drives and some buzzing from the keyboard. Test patterns
will also appear on the display between some prompts. This is normal.
User's Setup Procedures 105