IBM Personal Computer Manual To Operations page 216

26
Is the screen white?
YES - Have the unit to which the display was
attached serviced.
NO - Have the display serviced.
27
Turn the Brightness control fully
counterclockwise.
Brightness Control
28
Does the intensity of the characters decrease?
YES - Go to the next step.
NO - Have the display serviced.
9000-10 Test April 1984