IBM Personal Computer AT Manual To Operations page 265

Example 7 Color Display only
Screen Response
Audio Response
Action
+
1 short beep
See below
Screen has
=)
wrong color
or no color
If you are using a TV as your display, check that the
color is correct by disconnecting your TV from your
IBM Personal Computer AT. Operate your TV
n6rmally to verify correct color quality.
If
you have an
IBM Color Display, go to "Test 9000" in this section.
Note: If you are using your home television or
non-IBM display, it must be U.S. television system
(NTSC) compatible. Also, you may experience data
errors while using your diskette or disk drive. You
can correct this interference by moving your display
or TV a minimum of 31 em (12 inches) away from
your IBM Personal Computer AT.
Error Examples 2-21