Film-Tech Forum ARCHIVE: Question on Light Dimming

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Posted by Stephen Jones 1 (Member # 114) on 08-16-1999, 04:47 AM:

If anyone out there has CFS/Rentec Lamphouses and Automation, you may be able to answer this.

I have a problem in three of my theatres where the lights come all the way up to full bright during the middle of the movie for what it seems like no appearant reason. It occurs in every show at all different times, so I know it's not a bad cue. It ocurs with several movies in the same auditorium, so I know it's not the print, but the automation. I've cleaned the readers, checked the alignment and can't find anything. I asked the technician what the problem could be and he couldn't give me an answer of why this would happen. He suggested getting new dimmer boards for the problem projectors. I have a feeling it's probably something really simple that we've overlooked. The cues are read correctly. The lights go down at all the correct places; they just also come up during the movie and I can't lower them back down manually. So I end up flipping the dimmer breaker every show with these projectors. Hopefully someone out there can enlighten me. My dimmer boards probably won't be in for another two months and that seems like a long time to be flipping the breaker on and off every show.

Posted by Ken Layton (Member # 133) on 08-16-1999, 12:57 PM:

Have you checked with CFS/Rentec service dept?

It's possible that there may be a modification or update to the circuit boards. It's also possible that your equipment is sensitive to power line noise/spikes.

You could have a static electricity and/or grounding problem (ground loop).

Posted by Gordon McLeod (Member # 33) on 08-16-1999, 01:21 PM:

The Dimmer probably has more than one level ie full half and dim. Which level does it go up to
Then remove the relay in the automation for that level
If it still goes up check the wireing to the dimmer and for voltage spikes
Most dimmers will respond to transient line spikes and some will unlatch themselves
Also is there a remote tied on the lights from the fire alarm or cleaner stations check them as well

Posted by Brad Miller (Member # 2) on 08-16-1999, 01:40 PM:

How many screens does this happen on? I once had a CFS/Rentec automation with CE FM-35 failsafe that would do exactly that! It turned out to be a defect in the FM-35, and Component Engineering promptly sent out a free replacement for us.

If it happens on more than one or two and the building is not a new one, I'd think it was something else. Please give us some more info on this.

Posted by Jason Burroughs (Member # 68) on 08-16-1999, 01:59 PM:

I too have had problems similar to this when working with the CFS/Rentec automation and the Compnent Engineering Fail Safes. The problem turned out to also be the Fail Safes, according to Compnent Engineering, when the went defective, the became "ultra sensitive". As a demonstration of this the technician dropped a screwdriver on the floor near the projector, low and behold, it registered a cue detection. 1st thing I'd try is to replace the cue detector, if you don't have a spare, try swaping it with annother house that's not haveing a similar problem. If the problem follows the cue detector, BINGO there's your problem, just order a replacement. On the hand, I've seen the rheostats on the level adjustments become defective, where either the full dim or half light level will short and cause the lights to go up full. A shot of tuner cleaner seemed to help on this. Personally I'd start with the fail safes and move from there... Good luck

Jason Burroughs is a projectionist at the Loews Keystone Park 16 in Dallas, TX

Posted by George Roher (Member # 91) on 08-16-1999, 03:39 PM:

We have a theatre here with really old CFS automation that has the same problem. However it's a twin and the automation isn't really used. The operators dim the lights themselves and don't use any cue tape. But the dimmer has to be turned off during the feature on one of the machines or the lights magically come back up. With only 2 screens, it's no big deal.

Posted by Scott Norwood (Member # 30) on 08-16-1999, 06:40 PM:

Gee, we never had this problem in the single-screen with a 1930's-vintage Ward-Leonard resistance-type dimmer board! <grin>

I admit, though, that Brad is trying to convince me of the virtues of automation, and I am starting to agree with him, at least with respect to automation systems that _work_, unlike way too many that I have seen.

Posted by Brad Miller (Member # 2) on 08-16-1999, 08:52 PM:

Yup. It all depends on what you buy. Just because it is "automated" doesn't mean it's worth a flip. Personally I've never liked the CFS/Rentec automation, but I'm sure there are those out there who love it. I found it wasn't all that reliable.

Automation done right, however, can outperform a real live operator. (Notice I said "can".)

Posted by Rick Long (Member # 213) on 08-17-1999, 12:36 AM:

I wonder if your theatre has a remote dimmer-control station to allow bringing up these lights for cleaning? Possibly someone on the floor staff is hitting this switch in error.
If you have the time to operate the dimmers manually for a night or two, try disconnecting the dimmer control at the automation. At least this will help to isolate the problem.
Is there any co-relation between electrical storms in the area and this problem? Line-borne problems can often be alleviated with a couple of capacitors.
Just my two cents worth.

Posted by Stephen Jones 1 (Member # 114) on 08-17-1999, 12:49 AM:

I will try swapping out the cue reader/fail safes between the projectors and see what happens. It just happened two weeks ago to our biggest auditorium and now the lights come up all the time. I have a feeling that the reader is probably reading something that isn't there, ie ultra-sensitive. I've also had the problem with the lights flickering which I figured was the contact with the dimmer controls. Like you said, one squirt of contact cleaner made a world of difference. Thanks everyone, for the great response. This has been a thorn in my side and hopefully I can isolate it and get rid of it.