Dolby Laboratories CP650 Installation Manual Page 139

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Dolby
®
Model CP650 Troubleshooting Chart Maintenance and Troubleshooting
9-17
Symptom Probable Cause Recommended Action
You can hear pops or thumps during
projector changeover.
If the projector changeover relay power is DC, a diode
should be soldered across the winding of the relay to
prevent switching noise from leaking into the audio
wiring. This diode may be missing or defective.
If the projector changeover relay is AC powered, a
capacitor soldered to the relay coil terminals may be
defective.
Malfunctioning Cat. No. 772 board.
If possible, check that the diode is installed across the
relay winding. If you are familiar with such electronic
components, check to see that it is not defective. If the
diode is not present or if it appears to be open, install a
good diode. Activate the changeover and use a multimeter
to find the polarity of DC that appears on the relay coil.
Install the diode with the band end soldered to the positive
terminal. The diode should be a 1N4004 (1A, 400 V), or
1N4008 (1A, 800 V), or equivalent.
Install a 0.01 µF 600 V capacitor across the relay coil
terminals.
Call service engineer to correct the malfunction.
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