IBM 5155 Manual To Operations page 178

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