# Why are my lights flickering?

#### Stevens R. Miller

##### Well-Known Member
Well, yet another middle school is throwing curve balls at me. This one's system is based on a Lehigh DX2 with a rack control system (picture below) and a small architectural control processor with four faders (a master and three that each control a part of the house). The ACP has a Doug Fleenor Designs PRE10-A DMX512 10-Zone Wall Controller with ten presets and and an LED that indicates that it is passing DMX data through it (at which time it gives up control).

We plug our computer into the ACP (we're running QLC+ and using an Enttec OpenDMX), and things work as expected. But last night, we noticed one of the lights flickering. I thought it was arcing, but then we saw that others were doing it. As the evening wore on, it got worse, to the point where it looked like a disco did in my college days (late '70s). We thought maybe the computer was the problem, so we disconnected it. The ACP includes an "all on" preset, and a few others, including an "apron only" preset. When we activated "apron only," we again saw lights that should have been off flashing on and off. By "on and off," I mean a very brief "on" time, followed by anywhere from half a second to several seconds of "off" time. This is with no computer connected.

We cycled the power on the rack and the problem seemed to go away, but returned after a few minutes. Three of us were working on this and all agree that it seemed to follow the same progression each time we cycled the power: the problem went away, then returned after a few minutes, gradually growing worse. I will admit, however, that this observation is more anecdote than science. What is certain is that the problem always returned.

At the rack, each dimmer is in a module paired with another. Each has two green LEDs on it, labeled "A" and "B." We noticed that whenever a light flickered, its LEDs also flickered on its dimmer. We also noticed that, if all lights were off, there was no flicker. This was true when the computer was connected and streaming DMX data too: if even one light was up, others would flicker, but nothing flickered if we set the scene to total blackout.

We tried swapping dimmers that were flickering with others that weren't. The problem stayed with the slot the dimmer goes in, not with the dimmer. We concluded, therefore, that something upstream of the dimmer and downstream of the computer input, was sending sporadic signals of some kind. This would imply that most likely the culprit is either the ACP, or the rack module. We looked inside the rack to see if there was a DMX input downstream of the ACP, but what we found was not a five- or three-pin plug (there's actually just a terminal strip in there that the ACP apparently feeds into), so we couldn't connect downstream of the ACP.

Of course the school has put in a work order for service, but our show is supposed to open on Friday, so I am not optimistic that the contractor will visit before then, much less fix the problem. But we are stumped!

Any suggestions?

#### Amiers

##### Renting to Corporate One Fixture at a Time.
Flickering is generally a power issue or failing dimmer.

Take the fixture that is connected to that dimmer and run it to full. Wait 5-10 mins and start turning on other fixtures til it flickers that will tell you if its power.

Failing dimmer you can turn on the problem dimmers and set them at 35-50 percent. If they flicker the dimmer isn't doing it's job properly.

#### JohnD

##### Well-Known Member
Fight Leukemia
Have you tried calling Lehigh support? Granted they aren't ETC so I wouldn't expect that level of service but worth a try.
http://www.lehighdim.com/lw2/supconts.php
(Not to be snarky, but I question the wisdom of using "lehighdim" for their website, not really very positive.)

RonHebbard

#### microstar

##### Well-Known Member
Have you tried calling Lehigh support? Granted they aren't ETC so I wouldn't expect that level of service but worth a try.
http://www.lehighdim.com/lw2/supconts.php
(Not to be snarky, but I question the wisdom of using "lehighdim" for their website, not really very positive.)
I've had nothing but positive experience talking with Lehigh tech support on the phone even dealing with a discontinued product. They may not be ETC, but they've been in the lighting control business for over 50 years so they must be doing something right. Just sayin'

#### Robert

##### Well-Known Member
Air flow and heat build up can also cause cascading flickering. Check for obstructed air flow and bad fans. Knowing of the dimmer was going to full then off or from full to off could also indicate a bad dimmer module.

#### jhochb

##### Active Member
Good Morning Steve

Is this isolated to a few circuits?
If so, try swapping module to see if the issue moves. That will tell you if its the mod.

#### Mistermon

##### Member
I'm going to +1 Robert's post. Had that happen to me in a 70's ish auditorium with Colortran dimmers. Cleaned the air sensor and blew the dust out of the racks and problem was solved.

#### Stevens R. Miller

##### Well-Known Member
Thanks for the ideas, fellows! The problem does not move with a dimmer, but stays in the slot. That is, if I see the flicker on a given dimmer, and pull that dimmer out, then swap a different one that wasn't flickering into its place in the rack, the different one I swap in starts to flicker. But the flicker isn't limited to any particular circuit. It comes and goes all over the system. It also doesn't depend on load. I can bring up a single instrument and others (that should stay completely dark) will begin to flicker.

Now, here's where it gets more confusing: the school put in a "work order" on this, which usually means nothing will happen for at least 30 days. But someone must have pushed a bit, as an electrician worked on it yesterday. This was a school system guy, not a tech from the outside contractor that does theater support. The school was supposed to call me so I could watch the guy and help demonstrate the problem, but they didn't. In fact, no one was with him at all when he worked on it, so no one knows what (if anything) he did. But the director found out he had been there and asked me to rush in during rehearsal last night and test the system. I was unable to reproduce the problem.

Of course, when you are dealing with a flickering light, you only know if the problem still exists (because you can see the light flickering). You don't really know if the problem has been solved, because a light that isn't flickering right now might start to flicker again at some future time. As suggested above, maybe a good cleaning was all it needed and maybe their guy did that. But I can't tell, of course, because the rack is in a locked cabinet and getting them to open the cabinet for me is one of those things you only ask for just so many times before wearing out the good will you need to get them to do it.

So...

For the moment, it may be working. We have another rehearsal tonight, during which I will test it all again.

I should have mentioned this before, but yet another problem the rack has is that, after I shut down my computer and switch the ACP to "off," the cooling fan stops in the rack cabinet. Except that, after about ten minutes, it starts up again for a minute or so, then shuts down again. And it never stops doing this. About ten minutes off, then one minute on, over and over. I suppose it's possible that the rack (which is still on) builds up enough internal heat to trip a thermostat, which opens again after the fan has blown for awhile. If my other problem stays solved, I'll pretend that makes sense and ignore the fan issue.

As ever, the help I get here is much appreciated. (I hate working in the middle schools, but I love the help!)

#### RonHebbard

##### Well-Known Member
Thanks for the ideas, fellows! The problem does not move with a dimmer, but stays in the slot. That is, if I see the flicker on a given dimmer, and pull that dimmer out, then swap a different one that wasn't flickering into its place in the rack, the different one I swap in starts to flicker. But the flicker isn't limited to any particular circuit. It comes and goes all over the system. It also doesn't depend on load. I can bring up a single instrument and others (that should stay completely dark) will begin to flicker.

Now, here's where it gets more confusing: the school put in a "work order" on this, which usually means nothing will happen for at least 30 days. But someone must have pushed a bit, as an electrician worked on it yesterday. This was a school system guy, not a tech from the outside contractor that does theater support. The school was supposed to call me so I could watch the guy and help demonstrate the problem, but they didn't. In fact, no one was with him at all when he worked on it, so no one knows what (if anything) he did. But the director found out he had been there and asked me to rush in during rehearsal last night and test the system. I was unable to reproduce the problem.

Of course, when you are dealing with a flickering light, you only know if the problem still exists (because you can see the light flickering). You don't really know if the problem has been solved, because a light that isn't flickering right now might start to flicker again at some future time. As suggested above, maybe a good cleaning was all it needed and maybe their guy did that. But I can't tell, of course, because the rack is in a locked cabinet and getting them to open the cabinet for me is one of those things you only ask for just so many times before wearing out the good will you need to get them to do it.

So...

For the moment, it may be working. We have another rehearsal tonight, during which I will test it all again.

I should have mentioned this before, but yet another problem the rack has is that, after I shut down my computer and switch the ACP to "off," the cooling fan stops in the rack cabinet. Except that, after about ten minutes, it starts up again for a minute or so, then shuts down again. And it never stops doing this. About ten minutes off, then one minute on, over and over. I suppose it's possible that the rack (which is still on) builds up enough internal heat to trip a thermostat, which opens again after the fan has blown for awhile. If my other problem stays solved, I'll pretend that makes sense and ignore the fan issue.

As ever, the help I get here is much appreciated. (I hate working in the middle schools, but I love the help!)
@Stevens R. Miller Please tell us that the locked cabinet has adequate ventilation.
Toodleoo!
Ron Hebbard.

#### Stevens R. Miller

##### Well-Known Member
So did you call Lehigh tech support?
If I do that, I will be going around the school system electrician who is currently working on it. That's a proven way to make him mad, which I don't want to do. If he the problem comes back and he can't solve it, I may call them.

#### Stevens R. Miller

##### Well-Known Member
@Stevens R. Miller Please tell us that the locked cabinet has adequate ventilation.
I could do that, but I'd probably be lying to you. It does have vents in the back and there's a fair amount of space behind the dimmers and the back of the cabinet. The whole thing is years old. If it were going to fail (or, God forbid, ignite) for lack of cooling, it would have done it a long time ago. I do wish they'd installed the whole thing in the hallway, not just off stage, though. It's obnoxious to have to listen to the fan blowing through a whole show.

#### RonHebbard

##### Well-Known Member
I could do that, but I'd probably be lying to you. It does have vents in the back and there's a fair amount of space behind the dimmers and the back of the cabinet. The whole thing is years old. If it were going to fail (or, God forbid, ignite) for lack of cooling, it would have done it a long time ago. I do wish they'd installed the whole thing in the hallway, not just off stage, though. It's obnoxious to have to listen to the fan blowing through a whole show.
@Stevens R. Miller You're not alone. There is a Strand CD80-96 rack in a Catholic Basilica in Hamilton, Ontario, Canada. The rack was installed per specs from New York City designers as part of a total renovation after a fire demolished the entire interior of the church. There's the normal pipe organ at the rear of the church and a secondary set of pipes in an acoustically coupled niche high up the MSL wall. Someone decided the best place to locate the rack was jammed into this acoustically coupled niche where the fan noise was an immediate problem. Next step, the experts from NYC had the rack enclosed within a plywood "phone booth" with double walls and insulated with Roxul. Kept the noise in just fine. Kept the heat in too. One by one the dual-SCR blocks died. The experts from New York apparently prayed the rack would survive the warranty period. I haven't seen the rack in several years. The last time I saw the rack, it had slower fans installed and the "Easy Bake Oven" door was being left ajar. Let's see if I get in trouble for this post too.
Toodleoo!
Ron Hebbard.

Amiers

#### Amiers

##### Renting to Corporate One Fixture at a Time.
Well I would say if you got the Electricans number to give him a friendly ring and ask him out for a cup of coffee or lunch to pick his brain about what he did.

Make friends with the man and you won't need work orders for small stuff.

RonHebbard

#### Stevens R. Miller

##### Well-Known Member
...the experts from NYC had the rack enclosed within a plywood "phone booth" with double walls and insulated with Roxul. Kept the noise in just fine. Kept the heat in too.
My ham radio neurons are all thinking "Danger Will Robinson!"
My lawyer neurons are all thinking "Gross negligence! Punitive damages!"

#### Stevens R. Miller

##### Well-Known Member
Well I would say if you got the Electricans number to give him a friendly ring and ask him out for a cup of coffee or lunch to pick his brain about what he did.

Make friends with the man and you won't need work orders for small stuff.
Excellent advice. I'd follow it, too, if it weren't for the fact that I have just reached my limit when it comes to coping with middle school lighting systems. The company I am working with does one big show every summer in a high school. The high school has a drama teacher, which means most of its equipment is maintained quite well. Also, they have a catwalk and a scaffold, so we can replace any lights that burn out and/or redirect them, all without having to engage in any diplomacy.

Gonna turn 60 next year. I find the words, "I am too old for this sh_t" coming to mind more and more often, of late.

#### Amiers

##### Renting to Corporate One Fixture at a Time.
Just have to will it not to happen, Murtaugh.

#### RonHebbard

##### Well-Known Member
Just have to will it not to happen, Murtaugh.
@Amiers Perhaps I've missed your point. To my limited knowledge, the alternative to aging is death. I'm still going with aging as the better alternative.
Toodleoo!
Ron Hebbard.

TimMc