Film-Tech Forum ARCHIVE: Dolby CP 650 Sound loss

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Posted by Jean-Michel Grin (Member # 1360) on 10-19-2003, 05:39 PM:

Tonight (09:45 PM CET) a projectionist from our multiplex called me on my cellular phone while I was drinking a beer.
He told me that one of our CP 650 made a strange noise in the right channel, sounding like a open ground buzz. I tell him to check the external crossover, check if a connection in the sound rack was loose. After the projectionist checked all he call me again to tell me all was fine. God thanks, I thinked thad I had time to drink anoher beer, but the projectionist called me again to tell me that the sound was noisy, again and verry low. I told him to switch immediately to bypass to finish the show, and I will go to the theater to check the Dolby.
I left my beer and the bar, crossing the half of the city to go to the theather.
But I my only constatation when I rebooted the CP650 was that the sound was fine [Mad]

No ways to check the fault, even in the log journal...
The problem appears sporadicly, only when the unit is hot.
Did someone experienced the same in Yours theaters ?
Thanks for Your replies.
I called the projectionist at 12:00 PM and he told me that was alway fine again...
An I was back to the bar to drink another beer [Big Grin]

Bye,

Posted by Gordon McLeod (Member # 33) on 10-19-2003, 08:00 PM:

Alot of time rebooting any DSP system makes the problem go away
I have one theatre that has almost every device dsp and they finally had to reboot it every show [Mad]

Posted by Manny Knowles (Member # 1171) on 10-20-2003, 06:01 AM:

There's that joke about the computer engineers sitting in a car that wouldn't start and one of them says: "I got an idea. Let's have everybody get out and then get back in again."

Posted by Liam Utley (Member # 1931) on 10-21-2003, 06:52 AM:

Yeah i heard that joke... i think there was something about "closing all windows" in there too.

Is it definately the CP650 making the buzz? it could also be a speaker/amp problem. You said that the sound was "very low", it could be a problem with the HF driver in the right channel.

Posted by Jean-Michel Grin (Member # 1360) on 10-21-2003, 07:12 PM:

Tonight I re-checked all the connections between the cp 650 and the amplifiers with a signal tracer, but I din't found a fault.
For more accurate safety, I cleaned up all XLR connectors with a special contact cleaner, all sems be fine to me, but the projectionist told me again that yesterday the sound was loss again during the show and the only solution was to reboot the CP650.
I suspect an internal software failure, because we experienced the same problem in a another auditorium with a another CP650. It was promptely returned to Dolby for exchange under warranty.