Installation manual

Dolby
®
Model CP650 Installation Manual Digital Soundheads
6-2
6.2 Adjustment with Oscilloscope
Note: The Cat. No. 701 Digital Soundhead is optically aligned at the factory and
should not require adjustment unless the CCD Circuit Board has been disturbed.
The following test setup will enable adjustment of focus and confirmation or
adjustment of light level and optical alignment.
1. Make sure power to the digital soundhead is provided. Power to the CP650 should
also be on.
2. Open the CP650 front-panel setup access door.
3. Connect a probe from Channel 1 of an oscilloscope (with 20 MHz or greater
bandwidth) to the VIDEO Test Point, with the ground lead attached to the ground
test point.
4. Connect a second probe from the scope’s Channel 2 to the CLAMP signal test
point to trigger the scope. Connect the second probe’s ground wire to the ground
test point.
5. Set the trigger source on the scope to Channel 2.
6. Adjust the Channel 2 vertical trace position to move the trace off the screen. It is
not necessary to view this signal after triggering has been established.
7. Adjust the scope for one horizontal trace across the screen, and adequate vertical
gain (approximately 2 µs/div. horizontal, 1 V/div. vertical).
8. With digital film threaded and running in the projector, observe the video
waveform. (See Figure 6-2.)
6.3 Focus Adjustment
Cat. No. 701 (or 700) Digital Soundheads are factory adjusted and should not require
adjustment during installation. If the soundhead has become misadjusted, it may be
necessary to re-focus. Using the setup as above, adjust the objective lens/CCD
assembly in the reader head by loosening the 2 mm hex socket set screw (located
below the lens bore), which holds the lens/CCD assembly in place, then moving the
assembly back and forth. There are two methods for moving the assembly. A flat
blade screw driver inserted in the oval slot above the lens can be twisted to slide the
assembly. Alternatively, if the CCD circuit board cover is removed, the assembly can
be moved back and forth with your thumb and forefinger. The best focus is achieved
when the scope pattern has minimum brightness in the center of the trace. (See
Figure 6-2.) Look for the most “in-focus” display possible, while maintaining
minimum brightness inside the envelope. Setting the best focus will help minimize
the digital error rate.
Re-tighten the lens-holding screw.