IBM 5155 Manual To Operations page 183

17
Is your screen blank?
NO - Go to the next step.
YES -
Have the unit that the display was
attached to serviced.
18
Is your screen steady?
YES - Go to Step 21.
NO - Go to the next step.
19
Turn the Vertical Hold control clockwise as far
as it
will
go, then turn it counterclockwise until
the screen stops rolling and is steady.
Vertical Hold
Control
January
1984 Test 9000-7