Apple Macintosh Performa 577 - Manual (Page 158)

Adjustments Yoke - 37
2 Switch on the computer.
3 With one hand, grasp
the plastic yoke collar
and rotate it until the top
and bottom edges of the
picture are parallel with
the top and bottom of the
bezel.Switch off and
unplug the computer.
4 Discharge the CRT.
Plastic Yoke Collar