IBM Personal Computer XT Manual To Operations page 182

3
Set the Power switch on the system unit (and
expansion unit, if attached) to Off.
4
Turn the Brightness and Contrast controls fully
clockwise.
Contrast
Control
5
Turn the Vertical Size control fully
counterclockwise. A black area should appear
across the top and bottom of the screen.
, ----==--­
o
Vertical Size
Control
9000-2 Test April 1984