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Author Topic: Lamp strikes, house lights go out Thomas Pitt Master Film Handler Posts: 266 From: Leeds, West Yorkshire, UK Registered: May 2007 posted 02-25-2010 07:41 AM                     At my nearest theater, I've noticed that whenever the lamphouse strikes, the auditorium lighting for that screen briefly dims or even turns off - only to come on again when the bulb is working. This can also happen (to a lesser extent) if the lamphouse for the adjacent auditorium strikes. I'm assuming this has something to do with the power surge caused by the lamphouse turning on - but is this effect 'normal' for a multiplex? Is there anything that can be done to stop or minimize the effect? In this theater in particular, all the lighting comes from sconces on the walls, and to plunge the audience into total darkness for a second or two doesn't seem very professional... Incidentally, they used to dim the house lights a little bit when the advert reel started, then turn the lights off at the start of the trailers. Now, the lights remain at full brightness until the start of the trailers, at which point they dim and turn off.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 02-25-2010 10:00 AM                        Certainly not normal. It sounds like the rf from the igniter is getting into the dimmer input somehow. Might try capacitors on the input to the igniter and supression on the dimmer input. . . . .of course, I could just blame it on "slow" electricity. (50Hz). Louis  |  IP: Logged Jim Cassedy Phenomenal Film Handler Posts: 1661 From: San Francisco, CA Registered: Dec 2006 posted 02-25-2010 10:10 AM                     I've had two auditoriums where a slight short inside the lamphouse during ignition was feeding back to the dimmers through ground (I guess) and causing an effect similar to what you describe. In my case, one the high-voltage wires was too close to another metal part inside the lamphouse and when the igniter fired, a small spark was jumping from the high-voltage wire to ground. There wasn't enough leakage to affect bulb ignition, but it did cause the auditorium lights to momentarily dim. I also noticed it caused the platters in one of the booths to "jump" slightly. I could see the film tension changing during ignition. Once I found out what was going on, it was simply a matter of re-positioning the high-voltage wire away from other parts in the lamphouse and the problem was solved. Mabye you should check & see if you have a similar situation. Good Luck! >One more thing- - I located the short by turning off all the booth lights and striking the lamp with the lamphouse door open, but with the rectifier turned off, so that the bulb would not actually ignite. The "leakage" spark was easy to spot in the dark. You'll probably have to hold down or bypass the safety switch on the lamphouse door if you try this.  |  IP: Logged Paul Mayer Oh get out of it Melvin, before it pulls you under! Posts: 3836 From: Albuquerque, NM Registered: Feb 2000 posted 02-25-2010 12:25 PM                        Used to see an effect like that at an art house in the Melrose district in L.A. It was a changeover house, and every time a motor was started for a changeover, the sconce lights in the house would dim for a second or so.  |  IP: Logged Rick Raskin Phenomenal Film Handler Posts: 1100 From: Manassas Virginia Registered: Jan 2003 posted 02-25-2010 01:11 PM                     Just a thought: It sounds like the lamp strike might be momentarily loading down the power circuit and causing the dimmers to drop out. I don't know how the electrical codes in the UK would address this, but feeding the dimmers through a 1:1 transformer might serve to overcome the problem. And then that slow electricity might just can't be fixed.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-25-2010 01:14 PM                     I would suspect RF is causing the dimmer to misfire 1st disconnect the automation control leads to the dimmer and see if it still happens If it does then I would get some better supression on the lamphouse and probably add some bypass caps and gmov's to the input of the dimmer what make of dimmer is it  |  IP: Logged Geena Phillips Expert Film Handler Posts: 198 From: Norcross, GA / USA Registered: Apr 2006 posted 02-26-2010 04:21 PM                        We had a problem like this at one of our locations. The lamphouses all had AC igniters, and every time they'd strike, it would send out a pulse that scrambled the programming on the lighting automation. The only thing that ultimately solved it was replacing the igniters with DC ones.  |  IP: Logged Thomas Pitt Master Film Handler Posts: 266 From: Leeds, West Yorkshire, UK Registered: May 2007 posted 02-26-2010 05:54 PM                     It certainly looks to me like it's a direct result of a power surge from the igniter. On certain occasions, there's a little buzz/crackle from the stage speakers at the moment the lights go out. I doubt it's the dimmer, as the lights pop off/dim and then jump back on straight away, rather than fading up slowly like they do when the film ends. It also happens in every single auditorium when the relevant lamphouse strikes (not just in one), so a design flaw may be to blame...  |  IP: Logged Caleb Johnstone-Cowan Jedi Master Film Handler Posts: 593 From: London, UK Registered: Mar 2006 posted 02-26-2010 08:09 PM                     quote: Thomas Pitt Incidentally, they used to dim the house lights a little bit when the advert reel started, then turn the lights off at the start of the trailers. Now, the lights remain at full brightness until the start of the trailers, at which point they dim and turn off. It makes it easier to seat a screen that way when it's busy and my guess is you go to a vue and that's their company standard anyway. What you describe with the sconce lighting didn't happen at the vue I worked for or the ones I visited so my guess is it's a site problem.  |  IP: Logged Eric Robinson Jedi Master Film Handler Posts: 538 From: Santa Rosa, CA Registered: Jan 2005 posted 03-16-2010 01:34 AM                     You could use a scope to monitor the AC waveform supplying the dimmer. Make sure to set the time scale to "slow power" You would most likely see some spiking during the ignition phase if this is where the problem is.  |  IP: Logged David E. Nedrow Master Film Handler Posts: 368 From: Columbus, OH, USA Registered: Oct 2008 posted 03-16-2010 12:05 PM                        Maybe they have old Xetrol IVs sharing a ground. The manual for those talks about flickering, instability, and flashing. They have a section on it that calls for installing a "suppression network field". I only know this because I picked up two Xetrols recently, hoping to replace a non-functioning dimmer. Each of the Xetrols will control a different set of lights in the same auditorium. That, and I love to browse manuals. -David  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 03-16-2010 08:42 PM                        The problem is logically in the one lamphouse, since only it affects all dimmers. Look around the igniter and swap capacitors that are connected to the mains power input and the one DC wire that has a capacitor on it (not the one connected to the bulb.) The other lamphouses shoudl be the same. If necessary, swap igniters. Swapping is free. Then you can purchase what is needed. Louis  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 03-17-2010 02:30 PM                     quote: You could use a scope to monitor the AC waveform supplying the dimmer. Make sure to set the time scale to "slow power" [Wink] Eric, I cringe every time I see someone suggest using a scope on AC power. It is EXTREMELY DANGEROUS if you aren't 100% sure of how to do it safely!! Your scope inputs MUST NOT have ANY reference to ground, and you MUST isolate yourself and the scope to avoid getting a severe shock. If Thomas is not an experienced technician who knows every precaution necessary to do that safely my advice is DON'T TRY IT!! And I will not give out the procedure online as I will not be liable for someone getting hurt.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 03-17-2010 03:13 PM                     There is no issue with the scope probes being ground referenced since the measurements for noise are in refference to ground the normal calibration procedure of most dimmer cards is a dual scope one on the firing drive the other on the output Again it would be nice to know what dimmers are involved  |  IP: Logged Tony Bandiera Jr Film God Posts: 3067 From: Moreland Idaho Registered: Apr 2004 posted 03-17-2010 08:57 PM                     Gordon, I don't know if scopes or electricity behaves differently up there, but past experience and a few mishaps has shown me that your scope MUST be isolated from the AC power source's neutral, ground and hot or you risk getting bit or blowing up the scope's input circuitry. Using a battery powered scope is generally safe and the preferred method, or else connecting an AC powered scope with an isolation transformer. Looking at my post again I can see where the confusion arises, I should have said "the AC power source" instead of the "ground". And also should be "scope" not "scope inputs" as duh, you'd be using the inputs to look at the power.. I shouldn't post before eating dinner.. Forum would not permit me to edit that.... But the signal you're looking at, (unless you're looking for noise on the ground) should be referenced to neutral (Or the other phase of the AC line, in which case a fully isolated scope setup is mandatory.) For someone of your experience it would be safe to do, but it is not something that anyone should attempt.  |  IP: Logged

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