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Author Topic: No center channel Fernando Caldeira Film Handler Posts: 45 From: Lisbon , Portugal Registered: Mar 2010 posted 02-14-2015 07:54 PM                        We have - Nec NC3240s Doremi IMB Dolby Digital CP650 Cat. № 790 - Neutrik 110/75 ohm converter Problem: It has happen 3 times now and we haven´t been able to find the problem or even make it happen. Sometimes it just happens, and with the usefull help of the Murphys Law, allways with full house. The center channel just goes. nothing else happens. just the center channel. I go to the back of the processor, wigle the cables arround a bit and the sound comes back on. But I don´t think moving the cable around has anything to do with it. Have checked all cables, all 4 ohm converters, have removed cat790 and everything seems to be ok. Installer as no idea what it could be. We are going to start by changing the ohm converters. Does anybody have any ideas for what might be causing this? Thanks Fernando  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 02-14-2015 08:19 PM                     Can you post a picture of the back of the CP650 please so I can see the wiring (and more specifically the type of DB25 connector)?  |  IP: Logged Harold Hallikainen Jedi Master Film Handler Posts: 906 From: Denver, CO, USA Registered: Aug 2009 posted 02-14-2015 08:45 PM                        Does LFE disappear at the same time? If it were an AES/EBU problem, I'd expect them to disappear together. Good luck! Harold  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 02-15-2015 04:18 AM                     As Harold said, if an impedance converter was to blame, the LFE would disappear as well. I know it sucks but next time you'll have to check that when it happens (you can turn the amps off and check the 650's display to confirm. Keep a C/LFE CPL handy). But the main question is: when that happens, does the 650 still show centre channel activity on the main display? If so, your problem is after the 650 (or the 650 itself) and I would begin by checking the output wiring and maybe by swapping amplifiers. If not, your problem is elsewhere, probably the IMB or the cabling or the 650 itself.  |  IP: Logged Fernando Caldeira Film Handler Posts: 45 From: Lisbon , Portugal Registered: Mar 2010 posted 02-15-2015 10:37 AM                        Hey Brad, I´ll post the picture tomorow. Harold and Marco, Only the center channel goes, and it is inactive on main display. All the other channels keep working normaly on the display. One of the times it happened I switched the converters to see in another channel would stop workin but only the Center one was inactive.  |  IP: Logged Harold Hallikainen Jedi Master Film Handler Posts: 906 From: Denver, CO, USA Registered: Aug 2009 posted 02-15-2015 01:12 PM                        If the center goes away and LFE stays, I don't see how it can be an AES/EBU problem on the processor input. If the output indicator on the processor says the center is gone and the LFE is there, it seems like it's either in the processor or MAYBE routing in the server. If possible, it'd be nice to substitute another multi-channel AES/EBU source when the problem occurs and see if a known good source can drive the center channel. This stuff is lots of fun when it's intermittent. Good luck! Harold  |  IP: Logged Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 02-15-2015 04:30 PM                     quote: Fernando Caldeira Only the center channel goes, and it is inactive on main display. All the other channels keep working normaly on the display. So, the little bar graph of the Center channel drops to zero bars and stays there? Any other messages on the display? I'm just wondering here... what would be the expected behavior if the connection between the analog out of the CP650 and the amplifier behind it on the Center channel would be shorted?  |  IP: Logged Fernando Caldeira Film Handler Posts: 45 From: Lisbon , Portugal Registered: Mar 2010 posted 02-15-2015 06:03 PM                        Marcel so you´r saying switch the amps, say L with C, and see if L goes?  |  IP: Logged Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 02-16-2015 01:03 AM                     I guess switching the Center amp with e.g. the Left amp wouldn't be a bad idea. Because by process of elimination you can at least get a problem in your B-chain off your list if the problem remains the same.  |  IP: Logged Fernando Caldeira Film Handler Posts: 45 From: Lisbon , Portugal Registered: Mar 2010 posted 02-16-2015 05:11 AM                        Brad, here are the pictures. It´s a bit of a mess a I know but...  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 02-16-2015 06:07 AM                     This main audio out Y-Cable/adaptor looks a bit suspicious to me. However, if the signal goes away on the CP650 display already... - Carsten  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 02-16-2015 12:26 PM                     I think you are actually losing subwoofer too and you just don't realize it. In looking at that pic the DB25 used in the option input is the same type that has given me issues in the past. Once I replaced them, the problem went away forever. That's why I wanted to see it.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 02-16-2015 02:35 PM                     It's probably easy to overhear a missing LFE, but if the center signal disappears from the display signal indicator while the LFE signals stays visible there...? It's hard to imagine what goes on there. The 790 has such a pile of issues, but losing a single channel from an AES/SP-DIF pair... In theory one could assume a very weird channel mapping on the IMB, but who would do that ? There have been some reports of lost channels or swapped channels in certain Doremi firmware versions. - Carsten  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 02-16-2015 05:22 PM                     if you are 100% positive the LFE is there, I'd think of a CP650 issue or a Media Block issue. As it has been said, make sure you are on the latest version on your IMB. Make sure your ethernet cables from the Doremi IMB is as short as possible, that IMB does not like them - among many other things. Make sure your CP650 is running the latest sw - you may want to ask Dolby for the latest beta version (it won't be further developed) which drastically improves the 790 reliability. Finally, does the sound come back if you reboot the 650? I know it takes ages and you have patrons in the auditorium. I am not sure a bad connector could cause the issue you noted, if Brad is right and you are also losing the LFE, by all means your problem is likely to be the connector or a cold joint in it or the IMB adaptor.  |  IP: Logged Fernando Caldeira Film Handler Posts: 45 From: Lisbon , Portugal Registered: Mar 2010 posted 02-18-2015 05:26 AM                        Brad, I´ll try to have the instaler change de DB25. Marco, I´m 99% shure. Has It happened during a show and the stress lvls were high but I had that question on the back of my mind so i was paying atention to that detail. I will check the Ethernet cables and probably make new ones. As for the softwere I´ll have de instaler do it. A cold joint is like a bad welding? Thanks for all the help. I´ll keep you guys posted. Cheers Fernando  |  IP: Logged

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