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Topic: Stereo cell giving mono output
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Michael Pace
Film Handler
Posts: 64
From: Dalby, Queensland, Australia
Registered: Aug 2000
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posted 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.
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Pete Naples
Phenomenal Film Handler
Posts: 1565
From: Dunfermline, Scotland
Registered: Feb 2001
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posted 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!
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