Epson 20 - Manual (Page 155)

Character Set Check
To check your character set, press 3 and then Enter. The character
fonts that are included in the internal character generator display on
your screen. Compare your screen display to this illustration:
CHARACTER SET CHECK
Is the display correct (Y/N)?
After checking the character fonts, respond to the prompt:
Is
the display correct (Y/N)?
If the characters match the illustration, press Y and Enter. If you find
a problem with the characters on the screen, press N and then Enter
to display the error message.
Video Check
To check the video output of your monochrome adapter, press 4 and
Enter. This check displays two different screens: black and intensified
white. First you see the black screen; press any key to display the
intensified white screen. Then press any key to end this check.
You can use this test to adjust the size of the display on the screen.
The vertical and horizontal adjustments are located on your monitor.
Sync Check
This test is provided for service purposes only. If you accidentally
select this option, press any key to end the test.
Performing System Diagnostics C-11