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Author Topic: Dolby Digital/Surround Sound Problems Justin Schroepfer Film Handler Posts: 8 From: Moorhead, MN USA Registered: Dec 2010 posted 08-29-2011 05:50 PM                     I don't know what the problem is, but here are the symptoms: Recently, while playing a 35mm print, the sound has been switching back and forth from digital to surround, when it should just be staying on digital. This has happened on more than one print, but also seems to be sporadic: Sometimes the sound would be fine with a print, then later it wouldn't. However once it does happen, it doesn't go away for a while, but eventually will. Then it happens again... I've tried cleaning the sound head thoroughly and the light bulb in it was changed only a month ago. I need help diagnosing this problem so it can be fixed. If you need anymore info just ask and I will respond as quickly as possible. Thank you.  |  IP: Logged Tom Wienholt Master Film Handler Posts: 371 From: Towson, MD, USA Registered: Dec 2002 posted 08-29-2011 06:16 PM                     Have you noticed high error rates?  |  IP: Logged John Wilson Film God Posts: 5438 From: Sydney, Australia. Registered: Dec 1999 posted 08-29-2011 07:03 PM                     Equipment type and model please. A photo may assist.  |  IP: Logged Justin Schroepfer Film Handler Posts: 8 From: Moorhead, MN USA Registered: Dec 2010 posted 08-29-2011 07:48 PM                     Soundhead: Dolby Digital Cat. No. 700 Processor: Dolby CP500 Projector: Simplex 35/70  |  IP: Logged John Wilson Film God Posts: 5438 From: Sydney, Australia. Registered: Dec 1999 posted 08-29-2011 08:04 PM                     Does the film bounce about on its way to the reader? What error rate is the film reading in the 500? Does it fault? Has anything in this booth changed that could correlate with the arrival of the problem?  |  IP: Logged Justin Schroepfer Film Handler Posts: 8 From: Moorhead, MN USA Registered: Dec 2010 posted 08-29-2011 08:54 PM                     I found this in the CP500 manual. It describes the symptom perfectly... ...but it says the problem would be caused by a print without dolby digital, but the print we are using now played in dolby digital in the past. It also suggests that maybe the data blocks in between sprocket holes could be damaged, but the print is in very good condition so I doubt that would be the problem.  |  IP: Logged Manny Knowles "What are these things and WHY are they BLUE???" Posts: 4247 From: Bloomington, IN, USA Registered: Feb 2002 posted 08-29-2011 10:18 PM                     do you have another projector that you could use -- with this print -- to see if the problem goes away? if the problem goes away, then the fault is not with the print, but instead it would lie somewhere in that particular SRD system. Alternatively, do you have other SRD material you could try with this projector, to see if you get the analog reversion continuing to happen? The data blocks may look good to the human eye, but there may be enough going on there to confuse your system. Is there a predictable, repeatable pattern with the reversions to analog? does it happen in the same portions of the show? if so, that would point to damage to the SRD data blocks between perforations. in that case, there may be something in your film path that is scratching that area of the print. I've also seen this with improper threading of the reader -- lack (or loss) of tension. You are new to this website...are you also new to projection?  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 08-30-2011 12:45 AM                     Change the bulb in the CAT 700 soundhead, using the one from Dolby, NOT any other type/brand. Make sure it is seated properly in the holder. Check the condition of the electrical connections to the CAT 700 power supply and to the bulb..if any are loose/burned replace. Check the condition of the lightpipe with the CAT 700 lamp powered up..if it is yellowed or has dark spots, replace it. Gently clean the CAT 700 reader lens with a clean cotton swab. Make sure the reader is being threaded properly...especially if you have new booth staff that started work recently.  |  IP: Logged David Stone Film Handler Posts: 75 From: Hornsby, Sydney, Australia Registered: Jun 2008 posted 08-30-2011 02:59 AM                     Hi Justin, Do you have a SRD tag, trailer etc that you have run recently that did not fault ? If you do I would splice together a 8-10 foot loop that you can run thru the reader and projector. Run it for say 10 mins ocnstantly checking the error rate. Also I found using filmguard on a print to actually decrease error rates by cleaning the srd blocks on the print. Cheers, David.  |  IP: Logged Justin Schroepfer Film Handler Posts: 8 From: Moorhead, MN USA Registered: Dec 2010 posted 08-31-2011 05:19 PM                     Thanks for all the replies. I'll start looking at the things you have all suggested soon. We did move the problem print to another projector and will be played tonight, so if I have similar problems with this other (newer) projector then the print itself could be at fault. As for my projection experience, I'm not completely new but I'm not a veteran. At this theatre, I probably have the most projection experience, or close to.  |  IP: Logged Richard Hamilton Phenomenal Film Handler Posts: 1341 From: Evansville, Indiana Registered: Jan 2000 posted 09-01-2011 08:16 AM                     quote: Justin Schroepfer the light bulb in it was changed only a month ago Was it properly aligned and what are the error readings? Sounds like this could be the culprit. Rick  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 09-01-2011 11:58 AM                     I've seen light pipes get knocked out of alignment when one is lacing that reader..  |  IP: Logged Justin Schroepfer Film Handler Posts: 8 From: Moorhead, MN USA Registered: Dec 2010 posted 09-21-2011 05:31 PM                     UPDATE: The problem still exists. But, I have noticed now that the 'tension arm rollers' on the Cat. 700 sound head are wobbling and bouncing up and down much more than I think they should be. Could that cause the problem of not picking up the digital audio track and switching back and forth between surround and digital? Also, how could this problem be fixed? Thank you all, once again, for helping me out with this.  |  IP: Logged Ron Lacheur Jedi Master Film Handler Posts: 650 From: British Columbia, Canada Registered: Feb 2002 posted 09-21-2011 09:07 PM                     Most likely the airpot inside the 700 has been damaged. Call your tech.  |  IP: Logged Carl Martin Phenomenal Film Handler Posts: 1424 From: Oakland, CA, USA Registered: Feb 2002 posted 09-22-2011 02:43 AM                        what kind of platter do you have? does the problem correlate with what deck you're feeding from?  |  IP: Logged

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