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Author Topic: Sound problem - CP50 Serge Bosschaerts Film Handler Posts: 70 From: Schoten, Belgium Registered: Jan 2000 posted 11-28-2001 12:55 PM                        I have the following problem with my CP50 : From time to time the sound level just drops to about 50% of the level it was playing, after switching the unit off/on the level goes back to normal. This only occurs when projector 2 is playing, the sound is normal whith projector 1. The change in level is clearly vissible on the Cat.109 meters. Both projectors use the same DC supply so I think the problem may be in the Cat.108A pre-amp card. Any suggestions ? If indeed the Cat.108A is faulty would it be wiser to upgrade to a 108C version instead of sending the 108A to Dolby for repairs ?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 11-28-2001 02:08 PM                     Ya gotta be careful of the 108C. I have one that I cannot get to work in my CP-50. At least one other person on this forum has had the saem problem with the 108C as well. This could be a power supply problem in my case but have not had time to check it out.... In this system are there an LED reverse scanners? If so the problem could lay there in the power supply or current to voltage convertor PCB. It could also be an exciter lamp problem too. Check the exciter socket and exciter supply carefully. If you could provide some more particuluars that would help out too. What kind of sound pickup, projector, etc. Then we may be able to help you pinpoint it easier. Mark @ GTS  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 11-28-2001 02:23 PM                     I've also seen this happen with the 100K potentiometer being at fault. Since the CP50 uses an outboard fader, spending $2 at Radio Shack to check this possibility out is a snap. (However it should be affecting both projectors. Just something else to double check.)  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 11-28-2001 02:36 PM                     Speaking of the potentiometer I have seen the level pots(10 turn) on the 108's go bad and get noisy. This is another possibility. I don't think it is the master fader as the problem is only on the one machine. I'd swap projector inputs around on the back of the 50 and check the preamp that way. If the problem goes to the other projector, the preamp is at fault. If the problem follows the projector then there is a projector/exciter/or scanner problem here. Mark @ GTS  |  IP: Logged Serge Bosschaerts Film Handler Posts: 70 From: Schoten, Belgium Registered: Jan 2000 posted 11-29-2001 07:06 AM                        I'll check things out and will get back to you. Thanks already for the advice !  |  IP: Logged Serge Bosschaerts Film Handler Posts: 70 From: Schoten, Belgium Registered: Jan 2000 posted 10-15-2002 03:41 PM                        Well, finally found the time to fix my sound problem. I have replaced my cat.108-3 with a cat.108C card and the result is flat response up to 16Khz and the problem has disapeared. No problems with the power supply, my CP50 is a later model with the door droping down.  |  IP: Logged Steve Kraus Film God Posts: 4094 From: Chicago, IL, USA Registered: May 2000 posted 10-15-2002 03:59 PM                    Thanks for the update. (It could not have been the fader pot as others suggested since you saw it on the 109 meter/filter card.)  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 10-15-2002 11:45 PM                     Serge, You still have to watch the old Dolby Power supplys depending on the version. My door also drops down. That has nothing to do with which supply you might have in there. If you add a pair of CAT 280T's, a CAT 108C, and a CAT CAT 113C automation card you have to watch the supply rails VERY closely. The 280T cards suck up most of the available current then add the other two cards and the rails really begin to sag to the point that the unit no longer functions correctly!! I changed my original CP-50 red box over to a switching type supply thats available off the shelf. New surplus pricing was only 20 bucks U.S. or so. Another good indication of sagging power supply rails is that the red led's on the 113C card are not at equal brightness. Mark @ CLACO  |  IP: Logged Serge Bosschaerts Film Handler Posts: 70 From: Schoten, Belgium Registered: Jan 2000 posted 10-17-2002 04:59 AM                        Just checked the leds on the cat.113C and no sign of power sagging. My CP50 has the following cards : 108C,22,109,160,150B,64,117 and 113C. I use a SRA5 for Dolby SR.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 10-17-2002 07:59 PM                     You don't have any really power hungry cards in there. The CAT 280T's are what sucks up the current. The SRA5 is self powered, so in your case thats a good thing as your rails would have dropped seriously low. Mark  |  IP: Logged

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