Epson 10020 - Manual (Page 173)

Character Set Check
To check your 80-column character set, press 3 and Enter.
The characters that are included in the internal character
generator are displayed. Check the characters displayed on your
screen against this illustration:
After checking the characters, respond to the prompt:
Is the display correct (Y/N) ?
If the characters displayed match the illustration, press Y and
then Enter. If they do not match, press N and Enter to
display the error message.
D-16 Performing System Diagnostics