This is topic CP65 mixing Left and Center channels! in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Jesse Skeen (Member # 586) on 09-19-2000, 02:52 AM:
Here's a problem I've never seen before- one of the CP65's where I work is sending the SAME sound to both the center and left channels. I noticed it right away during a preview in DTS, but it also does it on analog stereo and even when switched into mono it still plays through both the center and left speakers! Nobody came to one showing in there tonight so I tried swapping cards from another CP65, but still the same problem. I even tried taking out equalizer cards, and with just the left one in it played the left channel through the left and center, same with just the center channel plugged in. I listened through the "Processor out" mode on the monitor, not the "Amplifier out" so I'm pretty sure it's gotta be in the Dolby unit somewhere, but I can't figure out exactly what it is so I gotta ask for help!
Posted by Brad Miller (Member # 2) on 09-19-2000, 04:20 AM:
What has changed recently? Could a tech have been in there and crossed output wires (look at the back yourself)? Has any modifications been made to the motherboard that you know of? When is the last time you know this unit was operating properly? You will find the answer quickest if you can track down anything that has been done to the processor since the last known date it was functioning properly. Any clues you can provide us will help.
Posted by John Pytlak (Member # 331) on 09-19-2000, 05:43 AM:
I agree with Brad. Most likely a simple case of "crossed" wires, or a short (piece of wire or solder) between two contacts (for the left and center channels).------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Posted by Neil Di Scala (Member # 592) on 09-19-2000, 07:30 AM:
Are you certain that it was playing in DTS when you were listening to it? If the symptom is analog only, this is an a-chain alignment problem.
Posted by Brad Miller (Member # 2) on 09-19-2000, 02:53 PM:
Good point. Turn off the exciter lamp or place a piece of masking tape/business card in front of the pickup to guarantee you aren't hearing the analog.
Posted by Gordon McLeod (Member # 33) on 09-19-2000, 10:49 PM:
Check the bypass relays on the back
When in bypass the same signal is feed to all three stage speakers
I believe Left and centre are on the smae relay
Posted by Jesse Skeen (Member # 586) on 09-19-2000, 11:36 PM:
I'll check tomorrow for "crossed wires", a loose wire was all that was causing a nasty hum in another auditorium earlier.
I suspect this problem has been there since the theater opened last year; nobody else noticed it, one person even said I must have good hearing to pick that up! 
I noticed it because I usually keep the booth monitor on center channel only, and on digital previews most of the time there is NO music at all in the center, but I was hearing it on this, then I saw the dialogue was also getting into the left channel. Switching briefly to analog revealed this wasn't a DTS problem, and having the problem persist in mono, where only the center channel should be on, has me stumped, but I'll check the amp connections closer and see what happens.
There have been a number of problems with this theater that I've already fixed having been there less than a week; what REALLY floored me was finding out least one analog sound reader was hooked up out-of-phase (again, ever since the place opened last year), so center channel sound was coming out of the surrounds and vice-versa! I noticed it during a trailer when I went there before I'd started working there, and thought it was one of those cheap 'stereo-izing' systems used for mono trailers! There's been so few analog-only movies out lately though that it must have gotten away unnoticed, but I caught it during a trailer with a bad Dolby Digital track! Think they were smart to hire me?
Posted by Ken Jacquart (Member # 369) on 09-20-2000, 03:11 PM:
I think Gordon may be right. Both Left and Right audio pass through the K1 bypass relay on the backplane. There are three relays there. Try swapping the positions of K1 and K2. If after doing so, you have same audio in Center and Right, you know it's the relay. Be careful not to bend the pins when you swap them... they're kind of delicate. Let me know if you need the relay and I'll send you a set.ken
Posted by Russ Kress (Member # 461) on 09-20-2000, 10:14 PM:
Ken and Gord are both right. This has happened to me before.I believe that it was Ken who told me over the phone what the problem was to start with.
When you put the relay in, you should be able to hear it "click".
Russ
Posted by Jesse Skeen (Member # 586) on 09-21-2000, 12:01 AM:
PROBLEM FIXED!
Turned out to be a problem with one of the QSC amplifiers, not the CP65. This theater uses that Smart stereo booth monitor that's hooked up pretty strangely, so I guess I can't tell where something's coming from by listening to the 'Processor' or 'Amplifier' modes like I used to- a loose wire on the back of one of these was what caused the buzzing in another auditorium.
Anyways, one of the amps runs the center and left channels, and someone had left the switch on the back in "parallel", when it should have been in "stereo"- it also has a 3rd position for bridged mono. Switching it to the right position fixed everything. I'm embarrassed I didn't figure that out quicker, but why do I suspect that problem has been there since the place opened last year?
Well, all I think is left to do now is EQ one of the CP500s, that should be fun!