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Author Topic: CP750 channel issue
Richard May
Phenomenal Film Handler

Posts: 1057
From: Floral Park, NY USA
Registered: Aug 2004


 - posted 05-30-2018 01:23 PM      Profile for Richard May   Email Richard May   Send New Private Message       Edit/Delete Post 
Has anyone had this issue? Center channel is being sent to left surrounds only. Bar graph on front says center channel info is present but audio is coming out of left surrounds. A reboot fixes it but after a while, it goes back. Non Sync also comes out of left surrounds only when I put decode mode to Center only.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999


 - posted 05-30-2018 03:11 PM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
I have a LOT of CP750s out there. Never had that problem. My biggest problem with the CP750 (and it hasn't been too huge) has been power supplies.

I hear that circa 2010 CP750s can have a problem where the level steadily decreases on the output though (still haven't had that one either).

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Leo Enticknap
Film God

Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000


 - posted 05-30-2018 06:05 PM      Profile for Leo Enticknap   Author's Homepage   Email Leo Enticknap   Send New Private Message       Edit/Delete Post 
I've had it, but it was left and right (stage channels) going to LS and RS. Again, a hard reboot fixed it. The unit in question just started to do this one day - no settings were changed, or anything like that.

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Tony Bandiera Jr
Film God

Posts: 3067
From: Moreland Idaho
Registered: Apr 2004


 - posted 05-30-2018 07:58 PM      Profile for Tony Bandiera Jr   Email Tony Bandiera Jr   Send New Private Message       Edit/Delete Post 
Richard and Leo, one question for you both: Are your CP750's on a UPS (or at minimum, a high quality surge protector?)

Reason I ask is, of all the screening rooms I and my former colleague have done, with CP650's and later 750's, we ALWAYS put the processors on a UPS with the projector electronics, and never had any such issues with either processor. (Not even the dreaded CP650 "robosound")

I firmly believe that since most projection rooms and cinemas in general have very noisy power, all it takes is for a rogue surge/spike/undervolt to make microprocessor based hardware do strange things.

A UPS, even a basic one, IMHO is cheap insurance against such problems.

Your actual mileage may vary, some assembly required, but at least batteries ARE included. [Big Grin]

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Dave Macaulay
Film God

Posts: 2321
From: Toronto, Canada
Registered: Apr 2001


 - posted 05-30-2018 08:19 PM      Profile for Dave Macaulay   Email Dave Macaulay   Send New Private Message       Edit/Delete Post 
If I remember correctly, there is some weird thing that happens when you use nonsync to centre only. Avoid that.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999


 - posted 05-31-2018 03:29 AM      Profile for Steve Guttag   Email Steve Guttag   Send New Private Message       Edit/Delete Post 
I do use surge protection on sound electronics but rarely UPS.

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Leo Enticknap
Film God

Posts: 7474
From: Loma Linda, CA
Registered: Jul 2000


 - posted 05-31-2018 07:46 AM      Profile for Leo Enticknap   Author's Homepage   Email Leo Enticknap   Send New Private Message       Edit/Delete Post 
I can't remember if the unit I experienced this glitch with is powered through a UPS or not. It is normally left on 24/7, though.

The venue in question was in Hawaii, and I was helping them by phone and Teamviewer to hook a laptop to their system for a one-off screening of video files from it.

They connected the Macbook to one of the cat745's HDMI inputs, and I talked them through setting the video frame rate and audio outputs correctly. The audio in their files was a L/R TV mix, and when they started to play, they reported that it "sounded funny, like it was coming from the sides of the room." I opened the CP750 utility on the remote access PC through Teamviewer, and sure enough, a signal was registering on LS and RS, but not L and R.

To rule out a problem with their files or laptop configuration, I had them play an audio CD through the BD player that was hooked to the other HDMI input of the cat745, and got the same result. It played through LS and RS. Then I asked them to make an analog connection from the laptop's headphone jack to the nonsync input, but they reported that they didn't have the necessary cable. So, basically, because I was out of all other ideas, I asked them to hard reboot the CP750. After doing that, it worked as it should: both the CD and the laptop played through L and R.

I was going to set it to L/R ProLogic and ask them if they preferred that or the plain L/R, but after that glitch I decided that it would be better not to tempt fate, and just play the L/R. Thankfully, the show went off without any problems, and as far as I'm aware, that CP750 has behaved itself ever since.

The next time one of us goes out there for a planned maintenance visit, it's on the list of things to do to play around with it and see if we can reproduce the fault.

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Magnus Eriksson
Expert Film Handler

Posts: 121
From: Stockholm, Hägersten, Sweden
Registered: Jan 2011


 - posted 05-31-2018 04:04 PM      Profile for Magnus Eriksson   Email Magnus Eriksson   Send New Private Message       Edit/Delete Post 
quote: Dave Macaulay
If I remember correctly, there is some weird thing that happens when you use nonsync to centre only.
That's exactly what happened to me when I tried to play mono muzak in nonsync five years ago. Random channel routing could occur on any input frome time to time.
quote: Dave Macaulay
Avoid that.
That's what Dolby support told me. It was a bug of some sort.
I configured nonsync to prologic and connected the mono signal to both left & right input. I've had no problems with random channel routing after that.

/M.E.

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Richard May
Phenomenal Film Handler

Posts: 1057
From: Floral Park, NY USA
Registered: Aug 2004


 - posted 06-01-2018 07:31 AM      Profile for Richard May   Email Richard May   Send New Private Message       Edit/Delete Post 
Thanks for the replies guys. It is indeed a "KNOWN" issue with the 750. Only one tech I spoke to at DOLBY told me about it. I can't believe this was not widely put out there before this.

If you configure Non Sync to use Format 71 (Center only), you are basically screwed until you reboot the processor. If you're switching between Dig 1 and Non Sync, center channel will randomly route to the Left Surrounds in the theater and sometimes distort, as per Dolby. A reboot fixes it until the next time it is rebooted.

There is no fix for this other than to not use Format 71. [Frown]

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