Dolby Laboratories CP65 - Manual (Page 29)

A-Chain Alignment Procedures
Step
No.
4-4
Indication Action
70 TO 80%
OF RATED VOLTAGE
a. Preliminary Procedures
✓
4
5
A-Chain Alignment Procedures
Notes
4-5
a. Preliminary Procedures
Remove the existing exciter lamp and replace with a new lamp.
Adjust the exciter lamp DC voltage to 70% to 85% of the rated voltage and verify that there
is no more than 3% ripple present with the lamp on, using an AC millivolt meter or
oscilloscope. Do NOT attempt to extend the exciter lamp life by running at too low a
voltage; the center of the slit may receive higher illumination than the edges, causing
signal distortion.
LAMP VOLTAGE DC ADJUSTMENT
6 V 4-5 volts
9 V 6.5-8 volts
If the projector uses a plastic light pipe or tube, verify that the light output is not appreciably
affected by dirt, cracks or flaws, yellowing, or foreign matter. Replace if necessary.
Place a white card at a point behind the film plane. Then adjust the position of the exciter
lamp until the image of the filament is centered both vertically and horizontally as shown.
You may find that obtaining an image of the filament is difficult in some projectors. Place
a piece of tissue paper over the lens to assist in seeing the image of the filament. Some
projectors do not use adjusting screws to change the position of the lamp; shims are
sometimes used for positioning.