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Author
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Topic: Missing right channel on analog (sometimes)
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Stephen Furley
Film God
![](http://www.film-tech.com/ubbmembers/1277b.jpg)
Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002
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posted 03-28-2010 12:14 AM
quote: James Waite one of the two green LED at the very left was dark which I believe means it was getting no signal from the right channel.
Can you confirm that these LEDs are on the Cat. 240A optical pre-amp card? This card has two LEDs which indicate signal present on the Lt and Rt channels; the Lt one is just above, and the Rt one just below, the centre of the card. If you're getting nothing on Rt at this point then it rules out everything after the pre-amp card. In general, the signal present LEDs on Dolby cards indicate that the signal is there at the input to that card, so the fault is before that card, but in the case of the pre-amp the fault could be on that card itself.
The far left slot in a CP-65 should hold a spare pre-amp card, since the processor will not work even in by-pass mode if this card is faulty. This spare card will have no LEDs lit; the next slot contains the active pre-amp card. Of course, it's possible that the spare pre-amp card is missing. If it is there, or if you have a spare card in another processor, power down and swap the cards. If you still have no signal on Rt, which will probably be the case, then the fault is with the soundhead light source, the cell, or the connections between the cell and the processor.
If swapping to the spare pre-amp does happen to cure the problem then you'll need to check, and possibly adjust, the Dolby levels. If you use a pre-amp from another processor then you should have the A-chain alignment checked, but you may not have the equipment to do this yourself.
You don't say if you're running one projector, or a pair, and if a pair, whether both machines are affected.
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