Film-Tech Forum ARCHIVE: Problem with Dolby CP-500

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Posted by Christian Volpi (Member # 2370) on 12-29-2004, 07:37 PM:

One of my theaters is having a problem with there Dolby CP-500. I haven't had a chance to make the 80 mile trek to listen to it but the projectionist told me that the 'dialogue' cuts out but the musical soundtrack is still audible. When he cuts all power to the unit and starts it back up it works fine. I'm assuming when he says that the 'dialogue' is cutting out I think he means that either the left, center, or right screen (or a combination of all three) is cutting out. Could this be a card? An amp? Any advice would be helpful.

Posted by David Yauch (Member # 2754) on 12-29-2004, 08:08 PM:

If it sounds fine on the booth monitor then it's a problem with the amps as far as I know. Here we have breakers by each projector so we can kill each channel one at a time and reset them creating only a minor disturbance, which usually fixes the problem, we use CP-500s as well. Anything to keep sound going is a plus. I know we've had this problem a couple of times due to shorts in the wiring for the amps, but the other guys here should be able to fill you with slightly more useful information.

Posted by Rick Long (Member # 213) on 12-29-2004, 11:24 PM:

My guess would be a bad centre-channel amplifier. This should be confirmable with the monitor (provided the monitor can monitor both processor and speaker outputs). Get them to run in by-pass for now, until you get there. (This should get you dialogue out the left and right stage speakers).

BTW. The 500 starts up in by-pass mode until it "kicks in". This is why you have sound at start-up.

Posted by Monte L Fullmer (Member # 2797) on 12-30-2004, 12:03 AM:

Also another possibility..and this could be the processor itself: The chassis backplane momboard could be giving you fits as well.

Shut the unit down, pull out all the cards, clean the contacts with a pencil eraser and reinsert the cards. See if that clears things up some. I've replaced two backplane momboards that developed hairline cracks in these CP-500's during my term with EDW's with similar problems.

If you want to see if amp problem is the source: switch wiring (either output or input) with another amp to see if the problem follows to that amp. If not, then you've "condemned" that area of the problem.

Next, is the switch out cards from another processor, one at a time between the two processors running some sort of dialog loop from a trailer for test,(course switching each unit off before card pulling...) to see if you can "condemn" this area of the problem. Even the power supply can be "condemned" if necessary.

There's lot's of possibilities that can be "condemned" to find lots of problems with sound - the "A" chain and the "B" chain of the line.

It's worth a try and an idea. good luck-Monte

Posted by Darryl Spicer (Member # 711) on 12-30-2004, 12:22 PM:

does your monitor have the abillity to check the source. Does it have processor mode or amp mode on it. If you hear sound in the processor mode but not in the amp mode then the problem lies in the amps. If you can hear no sound in either mode then the problem is in the processor.

Posted by Steve Scott (Member # 630) on 12-30-2004, 08:45 PM:

Monte's on the right path. One of my 500's did this on and off, throughout a few different films until I pulled everything and cleaned the dust off the boards. You should dust out thos units fairly regularly.

Posted by Maddison Lake (Member # 2876) on 01-02-2005, 12:51 PM:

I have two theatres on the CP-500, I hate the processors with a passion! The SDDS systems I have found has major compatibility issues with certain prints, for instance spanglish works great on them, and meet the fockers pops in and out like crazy. I have checked the amp system and it seems that it is fine. The SDDS systems are old, quarky, and malfunctions all the time, believe me, I have been begging for them to upgrade those houses to DTS soon. I still havent figured out my problem, any help would be great!

Posted by Thomas King (Member # 2745) on 01-02-2005, 01:13 PM:

Dialogue is mainly center speaker, try setting the box so that it sends center channel to left or right, that should tell you if it's an amp problem or if the box is glitchy. I'd also reccomend a through going-over of all the boards with compressed air and an anti-static brush for the pin connectors. Doing that improved our box no end.

Posted by Christian Volpi (Member # 2370) on 01-02-2005, 02:40 PM:

Thanks! I'll give your advice a try as soon as I can mosey down into that neck of the woods again.