This is topic Stereo cell giving mono output in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Christos Mitsakis (Member # 143) on 07-24-2001, 05:25 PM:
I am in the field teching a country open air cinema.
It's the first time such thing happens to me and I am a bit confused.
I've got a stereo solar cell that outputs in mono instead of stereo. I teched the same theatre last summer and it was ok. I can not tell what happened in the midtime and for shure no one is able to inform me about.
First thing I did is remove the cell and look for shorted wires. Nothing of that. The cell also looks ok (no crackings or dirt). Then I did A chain and looked ok. I threaded a stereo film and the problem is still present. Just plain mono, summing the two channels.
Anyone ever encountered similar problem in the past? Any thoughts?
Since I am in the field my reply might be somewhat late.
Christos.
Posted by Darryl Spicer (Member # 711) on 07-24-2001, 05:46 PM:
Hmmmmmm, If everything checked out with the A-chain and you are getting signal in both the left and right cell inputs and you are getting dolby tone on both channels of your noise reduction card then you should be getting stereo out of your processor unless there is something wrong with the matrix 2 to 4 channel decoding card. Did you check to make sure that the processor was not set in bypass mode. This will send everything mono.
Posted by Brad Miller (Member # 2) on 07-24-2001, 06:21 PM:
My initial gut reaction assuming that the processor does not have a problem and the wiring hasn't changed is that the cell is scanning one channel partially (and equally) on both cells. What are you using to guarantee yourself that you are actually scanning both tracks? Run a 97 test film and look at the reading on the scope. Can you give us more specifics, including the processor?
Posted by Gordon McLeod (Member # 33) on 07-24-2001, 10:02 PM:
Well if he did a a chain and it was okay then the problem is not the cell and also not the preamp
depending on the processor it could be several places
One nasty one I found once was someone hooked up a hearing impared system to the preamp output by parralleling them terminals and in doing so summed the two togather and gues what the system became big mono
Posted by Michael Pace (Member # 553) on 07-25-2001, 06:25 AM:
Christos,Check that you have not lost the common connection on the cell. The simple clue to this problem is a perfect azimuth reading on the 'scope when running the pink noise loop in the projector. Fit another cell to see if the problem goes away. It took me quite a while to figure that one out and nobody I asked had struck this problem before as they had most commonly replaced crashed cells.
Regards,
Michael.
Posted by Gordon McLeod (Member # 33) on 07-25-2001, 10:06 AM:
The problem with an open common is that when doing a Achain the cat 97 would have shown mono as well
Posted by Pete Naples (Member # 761) on 07-25-2001, 11:48 AM:
Now I once came up against this very thing. My client called me out on evening, as he had a strange sound problem, no stage channels, but the surround was loud and mushy. No output in 01 Mono or Bypass. This was a CP55 and two Fedi 35/70 XT's. Cat150 I thought, get there and swapping the Cat150 with a known good one did nothing, in fact neither did swapping any of the cards with known good ones. With on exception, the Cat240. With a Cat240 from a CP65 we got output in Bypass, so in Bypass my client went on the sheet. I returned early next morning to sort it out properly. Now with either Cat240 in the A chain showed a mono signal, but with the original Cat240, no bypass. I tried the suspect Cat240 in another processor, and guess what? It worked perfectly. After much head scratching I found the black wire on the cell was off. Resoldered and all was well. The moral of the tale is that with the ground off, with Cat240 you got no output in bypass or mono, in stereo formats you got no stage and all surround. With a 240A you get bypass but otherwise it was as Cat240. Other than that one has transformer input and the other doesn't I have no explanation for this, the other point is that with the black off, assuming we're talking about a dolby 50/55/65 here, from my experience, with the black off the decoder goes nuts! Even in mono. Remember that the decoder is not truly bypassed in mono, it's still in the signal path. So all that points to is that our friend probably doesn't have a cell or pre amp problem. Like Gordon said. If it's a Dolby, how about a faulty control logic card, wich is putting the Cat 150 into mono, even when the front panel says stereo? Or the Cat 150 is monoing regardless of control. I guess at a push the Cat222 could mono the signal also, but I'd have though that this would show up on the meters (unable to set dolby level for each channel individually)Christos, looks like you've got a bit of work ahead of you with your scope and a signal flow diagram!
Posted by Christos Mitsakis (Member # 143) on 07-25-2001, 04:18 PM:
Thank you all for replying.
The processor preamp is OK.
Gordon IS right. I've got mono signal with cat 97.
So I return to my first speculation. Shorted wires or as you diagnosed open common lead.
In XY mode with cat. 97 I should normally have a cross trace, instead I have a "scissor" trace, that comes and goes (ie "scissor effect" - "slash line" and vice versa)thing that makes me believe that something is happening with one channel. In dual trace mode I've got full modulation in both traces (ie. mono signal) folowed by half modulation again in both traces. This indicates that one channel has less light from exciter or something else is happening in the cell.
If I am to replace the wires How close to the cell can I go with the soldering iron?
Regards
Christos.
Posted by Gordon McLeod (Member # 33) on 07-25-2001, 06:23 PM:
Try connecting you scope on the cell leads with them disconnected from the processor. If you turn up the scope's gain you should see the output of the cell (There may be a lot of noise present as well) and run the cat97. This will rule out a problem in the processor
Posted by Rick Long (Member # 213) on 07-25-2001, 08:24 PM:
I had exactly the same thing on a new installation with a C.N 165 cell for Cinemeccanica. Cell looked fine, but only a mono output from it. Visually, it looked normal. Running short of time and confused as to what the cause might be (running into a CP-45), I replaced the cell with another one I happened to have in my trunk. Worked fine.The original monoized cell is in our shop waiting for time to investigate further.
Posted by John Eickhof (Member # 323) on 07-26-2001, 01:57 AM:
Check the Slit Lens for oil! Look at the image of the light and make sure you have the full slit width of light present! If the lens gets oil in it, you will have feeble readings from the cell! Good luck!------------------
John Eickhof President, Chief Slave
Northwest Theatre Equipment Co., Inc.
P.O.Box 258
Wendell, ID. 83355-0258
208-536-5489
email: jeickhof@nteequip.com
Posted by Stan Gunn (Member # 554) on 07-27-2001, 01:20 PM:
Hi Christos
I had a simular fault some years ago on a U3, only mono would be produced.
At 2am after running a full shift at another site I discovered a coating on the cell surface, after carfully removeing the coating and then polishing the cell it worked fine, and still is.
Dont know what the coating was, but I had to scrape it of with a razor blade. Have close look at the cell under a glass. 
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