Dolby Laboratories CP650 Installation Manual Page 126

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Dolby
®
Model CP650 Installation Manual Maintenance and Troubleshooting
9-4
Clamp (Trigger) Trace
(CH2)
Light through perf holes
VIDEO TRACE (CH1)
Left Graticule
Right Graticule
Data
SET HORIZONTAL SWEEP
Figure 9–5 Scope Display of CP650 Video Test Point Signal
3. Adjust the LED Position.
a. Switch the Channel 1 video input coupling back to DC.
Figure 9–6 Adjust LED Assembly for Optimum Video Signal
b. Loosen the 2.5 mm hex screws and carefully rotate the LED assembly while
watching the scope image. Adjust for maximum video signal voltage
(unobstructed light through the perf hole) on the upper trace. Also, the
waveform must be reasonably flat. (It should fit within one scope major
division.) In other words, adjust for peak voltage with minimum ripple.
4. Check/Set LED drive current.
The optimum peak video signal voltage (unobstructed light through the perf hole)
is 4 V, measured from the 0V reference baseline to the upper trace. If necessary,
adjust the Cat. No. 701 power supply output to achieve the correct video voltage.
See the Figure 9–7 for adjustment location (VR1). The back cover of the digital
soundhead must be removed to gain access to the output adjustment.
Output Adjust
(VR1)
Figure 9–7 LED Drive Current Setting
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