Control/Dimming Flickering Lights

We're having trouble with flickering from six of our dimmer-controlled lights for the past month. The issue happens seemingly at random except that it is far more likely to happen when multiple instruments are adjusted at the same time. These instruments need not be the instruments that flicker: it seems to happen most often when we are adjusting our cyc lights using faders, and none of those channels is involved in the flickering. Sometimes it will be a brief flicker; at other times it will persist for 1-2 minutes or until we adjust the levels. There have been no electrical changes except that we moved a couple of pipe-mounted outlet boxes.

Our setup:

Strand C21 48-module rack with single C21 Processor unit
48 Strand Dual 2.4kW Standard dimmer modules
Compulite VectorOrange Control Console

We also have a programmable bypass wall panel for our house lights (channels 95 and 96), but that does not seem involved.
 
First of all welcome to the booth! Be sure to introduce yourself over in new member land!

As for your problem, sounds like a DMX or console issue, but it could also be power related. How energetic is the flickering, I.E are the lights just flickering subtly or are they flashing widely? Are you using proper DMX cable and a terminator? Sorry if it seems like im grilling you here, its just that more details can often make solving these kind of problems much easier. Again, welcome to the booth, I hope we can help you out!
 
Thanks, and don't at all worry about grilling. I'll try to answer your questions as best I can, but I must confess that I inherited this system four years ago and have been learning on the job. The 'energy' of the flickering varies, but it's not subtle: you could get a similar effect by tapping a blackout flash key. Sometimes it will happen once (a brief flicker and then back to level); other times it will keep flashing randomly 2-3 times a second for anywhere from a few seconds to a minute or so.

We have proper DMX cable to the wall panel, but I do not know what they used in the walls. We've been using it for eight years without issue.

I do not know about a terminator; sorry if this is a n00b question, but where would such a thing be located?

We have 10 coemar moving heads; could their configuration affect the dimmers?
 
If you are using 3 pin connectors from the lights to the buss - when was the last time you cleaned them? We had a bunch of issues until we went through and took a fine emory cloth to all the pins. Over time they must build up a little oxide.
 
I remember our whole rig did a similar "flash" looking effect that you describe (everything would dim and jump back at the same time).
We looked high and low for a solution... turns out that dimmer racks don't like dust! who knew :rolleyes:

Anyways... Now because of that experience, that would be one of the first things I'd check. It could be coincidence that they are doing it when you control a particular channel. You could also try re-seating all the everything.
 
If you are using 3 pin connectors from the lights to the buss - when was the last time you cleaned them? We had a bunch of issues until we went through and took a fine emory cloth to all the pins. Over time they must build up a little oxide.

It has happened with different instruments on the same channel and doesn't follow the instruments, but I will look at them.

I remember our whole rig did a similar "flash" looking effect that you describe (everything would dim and jump back at the same time).
We looked high and low for a solution... turns out that dimmer racks don't like dust! who knew :rolleyes:

Anyways... Now because of that experience, that would be one of the first things I'd check. It could be coincidence that they are doing it when you control a particular channel. You could also try re-seating all the everything.

We'll pull the processor and the affected dimmers today and see what they look like.
 
All of the previous suggestions are good ones. One more to check. The circuits that are flickering, do the flicker when they are at [Full] ? If they flicker at lower levels and not at full, there is a good chance that the zero crossing detectors are seeing unclean power. Any device that has a builtin switching power supply, could be causing the problem. If there is a bad capacitor or diode, the supply could be puting trash on the powerline and the zero crossing detector gets confused when it sees that trash. When lights are at full, that seems to not be an issue, or so slight that it is not seen. I have had the problem with one of my Wybron coloram supplies. It took a bit to find it. I would suggest trying your system without any moving lights, LEDs, Scrollers or anything else that has a builtin switching regulator supply. If that clears it up, then put the devices removed, back one at a time and check with a fair number of conventional set at various levels. If no problem continue to add back devices one at a time.
 
I had one more thought that just happened recently. We installed a new follow spot that has its own built-in dimmer. So we broke the DMX chain from the console to the main dimmer rack to insert the spot. Some lights then developed a mind of their own. Turns out, when the follow spot doesn't have power (its not used in all shows) it was messing up the DMX. Not all the time and not the same lights. So now if it's not in the show, we replug the DMX line to bypass it.
 
Thanks. I just had a thought; I know one of my techs recently replaced some 3-pin xlr audio cables that someone at some point had used to chain some of our movers together with proper DMX cables. I wonder if he changed the order of the fixtures in the chain. Is there some sort of terminator setting that is needed for the last mover in a DMX chain? If so, maybe he inadvertently messed up our termination.
 
Thanks. I just had a thought; I know one of my techs recently replaced some 3-pin xlr audio cables that someone at some point had used to chain some of our movers together with proper DMX cables. I wonder if he changed the order of the fixtures in the chain. Is there some sort of terminator setting that is needed for the last mover in a DMX chain? If so, maybe he inadvertently messed up our termination.

Are all of your DMX devices on the same universe? It could be something is overlapping addresses or a DMX cable is going bad. Could also be a unit being sad. I would disconnect anything DMX'd beyond the dimmer racks (I assume those are first in the DMX chain), and see if you can get it to flicker. If not, then it's likely a problem beyond the dimmers. Start testing each device individually by plugging in one at a time and see when the conventionals starts to flicker.

If the dimmers still flicker with all the devices following disconnected, then it's most likely a dimmer problem. Try only connecting one rack at time and see if you can figure out if it's one rack or not. If all racks are flickering, it's probably either a DMX cable or a board. Try using some other DMX cables, if it's still a flicker problem it's likely a board issue. Make sure all the terminator switches on the dimmer racks are in the off position (if there are any).
 
So here's an update after two hours of work today.

First we disconnected all ten moving heads from DMX. No change.

We removed and cleaned the processor, all 48 dimmer modules, both filters, etc. and cleaned the entire inside of the dimmer rack. Put everything back together. Dimmer modules were not necessarily put back in the same locations. No change - same channels with issues.

We then experimented with different combinations of dimmers on and off. After a short while we discovered that with our cyc lights turned off we could not duplicate the problem. These are four Altman SkyCyc 3 strip-lights for a total of 12 channels. We haven't had time to narrow it down to individual channels, but if we turn on any one color alone (every third channel) it does not seem to do it; if we have any two colors on (8 channels total), it does. We're going to sit down with it some more on Monday and see if we can narrow it down any further.

Any one have any idea why these four instruments might be causing the problem?
 
Are all of your DMX devices on the same universe? It could be something is overlapping addresses

Yeah, one universe. Dimmers are channels 1-96, the movers are 14 channels each starting at 100. No overlap: I've checked and rechecked.

or a DMX cable is going bad.

Unfortunately, I dont have a spare 5-pin cable. Thats on my list.

I would disconnect anything DMX'd beyond the dimmer racks (I assume those are first in the DMX chain), and see if you can get it to flicker.

Done (see above). Actually, our console runs (after a long cable run) into an 8-way Pathway eDin opto-splitter. From there it goes out to 1) Dimmer rack 2) six DMX-3 output boxes throughout the theater.
 
It seems really unlikely that the problem is the skycyc's themselves as in the end they are just a light fixture. I suppose it could be a problem with the plugs or outlets needing cleaning or an electrical short of some sort. Try plugging some other fixtures into those circuits. I bet it'll still happens indicating the problem is either in the cable between the dimmers and the fixtures, in the rack, in the DMX line, in the console.

Flickering is often a sign of a dmx problem. But not like the one you are describing. Usually what happens is if you get a long line of DMX devices without a terminator on the end, the DMX signal goes up the line and then echo's back down it creating a mixed signal, confusing the fixtures and making them flicker. But this would not come and go depending on which fixture is turned on.

I would be looking at the C21 processor unit and the light board.
Has someone messed with the dimmer curve on those circuits?
Is there factory reset you can do on the light board?
 
So here's an update after two hours of work today.

First we disconnected all ten moving heads from DMX. No change.

We removed and cleaned the processor, all 48 dimmer modules, both filters, etc. and cleaned the entire inside of the dimmer rack. Put everything back together. Dimmer modules were not necessarily put back in the same locations. No change - same channels with issues.

We then experimented with different combinations of dimmers on and off. After a short while we discovered that with our cyc lights turned off we could not duplicate the problem. These are four Altman SkyCyc 3 strip-lights for a total of 12 channels. We haven't had time to narrow it down to individual channels, but if we turn on any one color alone (every third channel) it does not seem to do it; if we have any two colors on (8 channels total), it does. We're going to sit down with it some more on Monday and see if we can narrow it down any further.

Any one have any idea why these four instruments might be causing the problem?
it could be they're pulling too much power, maybe they all happen to be on the same leg or something?
 
It seems really unlikely that the problem is the skycyc's themselves as in the end they are just a light fixture. I suppose it could be a problem with the plugs or outlets needing cleaning or an electrical short of some sort. Try plugging some other fixtures into those circuits. I bet it'll still happens indicating the problem is either in the cable between the dimmers and the fixtures, in the rack, in the DMX line, in the console.

Oh, I didn't mean to suggest that it was the fixtures themselves. But those particular channels seem to be the ones causing the issue. We can certainly try putting some other instruments on those channels, but we don't have anything else that will pull 1500W/channel like the SkyCycs.

I would be looking at the C21 processor unit and the light board. Has someone messed with the dimmer curve on those circuits?

Unfortunately for that we'd have to get the folks from Strand out. And, no, that cabinet is locked and I'm the only one with the key. Nobody's been messing with any setting in the rack.

Is there factory reset you can do on the light board?

The light board runs on Windows XP embedded. I don't know of any sort of factory reset short of reformatting and reinstalling...and that would require significant reprogramming.

it could be they're pulling too much power, maybe they all happen to be on the same leg or something?

Hmm. Maybe, but we've had a lot more load on there in the past than we currently do. Even if we had everything at full right now it would only total about 24kW.
 
Unfortunately for that we'd have to get the folks from Strand out. And, no, that cabinet is locked and I'm the only one with the key. Nobody's been messing with any setting in the rack.

Well if it's been locked that kind of answers that question, but you shouldn't need anybody from strand, there are plenty of places around that could do maintenance and check the dimmers for you.
 
It also would not hurt to reboot the dimmer rack. Even the most stable, microprocessor based system can get a snit and need its head cleared. Always try the simple, easy stuff first.

Since you have an active splitter, that eliminates the movers and their cabling. It narrows the search to the console, the splitter, the dimming rack, and the DMX cabling between the three.

Is the DMX cable from the splitter terminated at the dimmer rack? There should be resistor across the DMX line at the terminal strip inside the rack. I would also check that the switch for termination is turned on for the splitter input.

It could also be a power problem. Are all of the lights that cause it to act up powered from dimmers on the same phase? Assuming this is a three-phase rack, phases are bussed to columns of dimmer modules, in the pattern left to right A, B, C, A, B, C. If the culprits are all on the same phase, then consider having a qualified electrician inspect the feeders to the rack and the circuit breaker for it.
 
Well what a conundrum wrapped in a pickle.

You could try re-patching the board / trying a different board? If the same channel in the board is doing it it might be the board, but if it does the same instruments / circuits its outside of the board... Idk if that makes sense...
 
I logged this earlier, now disappeared, the most obvious, common problem causing flickering is a bad neutral connection in the dimmer and this could cause load related flickering, another vaguely possible fault is an earth neutral swap on a light, sending current down the earth and lifting it.
 

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