Control/Dimming Pulsing Dimmers - This one is a major head scratcher.

Fluxion Designs

New Member
Hello everyone,
I've used this board in the past and appreciate all the good expertise here. I've posted in the past, but for some reason my account isn't being recognized at all, so I had to start a new one. Apologies for that.
I'm working with a venue who are having what is a fairly common problem, but it's blowing all attempts at trouble shooting out of the water. I'll describe what's happening and all the tests and fixes that have been attempted - I apologize for the length of the post, but if I don't list everything, then I'll get a lot of advice to try things that have already been covered...

The venue is a small theater in a converted industrial/office complex. The conversion was done on the cheap, and the theater was outfitted as follows:
ETC Express 125
Blizzard Lighting Pipeline taking one DMX input from the console and splitting out to 5 lines to 5 electrics
3-pin DMX cable (not mic cable) running lengths from 12' - 50' to the various electrics.
Each electric has a mix of Elation DP-DMX-20L (4 channel dimmers - either 2 or 3 per electric for a total of 12) and ADJ Flat Par Tri18x LED fixtures (a cheaper end 8-bit RGB fixture). Two electrics have 5 of the TriX's, the other four have none.

Fixtures are connected with the same sort of 3-pin dmx cable. as the runs to the electrics.
Each Elation dimmer pack powers from 2-3 ETC conventionals, either Parnels, S4 Jrs, or S4s. All instruments are running standard 575w HPL lamps.

The problem:
About a year after they opened, the venue started having trouble with two of the dimmer packs flickering. When I checked it out, it was more of a regular pulsing than flickering, and it manifested most strongly when the dimmers were run at low power than when at full. They weren't paying me, so after a short bit of troubleshooting, that couldn't isolate the problem, I simply ran the instruments in those dimmers to packs that were working properly and told them to call me when they had some downtime and some money to hire me to do some real troubleshooting.

Of course they never called back, but about six months later after that, January of this year, they called me back and said they were having the same problem again. This time when I went in, it was the same regular pulsing but now in 5 dimmer packs (of the 12), spread throughout the theater. The two I had bypassed were still unused.

Since the problem was manifesting randomly through the space, it didn’t seem like a console issue, so I started by isolating electrics and fixtures, expecting that the problem was a bad instrument or cable, and that if I took it out of the system, the others would behave properly. No amount of disconnecting ever solved it, all the way to running a new DMX line straight to one of the problem dimmers with no other outputs on the console. The pulsing persisted. In doing this I also tried using the two dimmer packs that had caused problems earlier in the year, and both behaved just fine.

Unable to find a bad unit or cable and with dimmers that had been an issue in the past working now, I went back to wondering if it was the console. After trying switching addresses on the packs, to confirm that the pulsing wasn’t in particular addresses, as well as switching DMX outputs and changing the DMX speed in the output configurations, I brought in a different console – an Express 250 that I used all the time. There was no change.

I then did some more isolating, moving instruments, balancing, and unbalancing loads, trying to find a culprit without any luck, then brought in terminators for all of the electrics (even though the elation dimmer packs are supposed to be self-terminating), with no change. I then rented a different DMX splitter from the local lighting shop and tried running through it (even though I’d already tried taking it out of the chain), again with no change.

At this point, even though the problem seemed bigger than the individual dimmer packs, but with the venue freaking out a bit with a show loading in the next day, I bought a new pack from the local music shop – a cheaper ADJ version of the same 4 channel dimmer pack. Replacing one of the problem units with the new one (and replugging everything exactly the same way) solved the problem. That unit didn’t pulse. Despite not being totally happy with the solution, I told the venue to buy replacement packs for each one that was pulsing and switch them out. They did that last week, and the show that was moving in proceeded with no problems through the weekend.

The problem returns:
Tonight I got a text from the venue manager saying that tonight, seven of the 12 dimmer packs started pulsing again – a mix of the new, replacement ones and some of the old ones that had been fine until now.

My only thought at this point is that something bigger about the space is affecting the dimmer packs in weird ways. I’ve told them to try running lights without the AC or heat on tomorrow, to see if perhaps there is an issue with the power in the building, and the motors from the cooling units affecting the power running to the dimmer packs, but aside from that, I have no idea where to go from here in terms of solving the problem for real. I can rent a DMX tester and check the signal arriving at the packs, but having taken literally every part of the system out of the chain at some point without losing the pulsing, I don’t know what good it will do.

And so friends, I ask… Anyone run into problem as big as this anywhere else? More importantly, did you solve it?

best to you all from Austin,

Last edited:


Resident Curmudgeon
Senior Team
Premium Member
... then brought in terminators for all of the electrics (even though the elation dimmer packs are supposed to be self-terminating), ...
Unsure where you're getting your information. There are only a few "self-terminating" devices, all from a manufacturer that's not Elation. From the DP-DMX20L manual:
It is recommended that the last pack or fixture in line include
a DMX terminator into the output. A DMX terminator consists of a 120 ohm, 1/4
watt resistor soldered across pins 2 & 3 of a standard 3 pin XLR connector.
But not the issue in this case.

Suspect some sort of noise on the line is messing with the zero-crossing circuitry of the dimmers.

Fluxion Designs

New Member
Suspect some sort of noise on the line is messing with the zero-crossing circuitry of the dimmers.

Yes, the person who installed the venue told me they were self-terminating, but obviously I didn't totally buy it, since I went through and terminated everything. But as you say, obviously not the issue. Line noise is the reason I've asked them to try the system with the AC and heat on and off, as those motors are the most likely culprit of anything strong enough to cause this. Assuming that line noise is the issue, I don't necessary see options for any easy fix, aside from buying all new, better dimmers or conditioning the power to each dimmer pack, which would likely be as expensive as buying new dimmers.



Well-Known Member
I had a somewhat random pulsing in a venue that was related to poor wiring in the panel and poor balancing of the venues equipment. It would start on a few dimmers and them proceed to take over every dimmer. Theses were 2 rack mounted units. This happened in the evening when the HVAC, ice machines, and drink machines were all in high demand. My solution was getting better power that was isolated from the surges produced by all the appliances. Look for trash getting into the neutral line. Can you borrow a ETC Smart Bar or Leprecon dimmer pack and see what happens? Just wondering if a manufacturer with "better" electronics might offer some better results.

Fluxion Designs

New Member
Can you borrow a ETC Smart Bar or Leprecon dimmer pack and see what happens? Just wondering if a manufacturer with "better" electronics might offer some better results.

I can borrow or rent some nicer dimmers, but as noted, almost anything is likely going to work normally when first connected. The original Elation dimmers all lasted a year or more before they were affected, while the cheaper ADJ ones lasted about a week. They are telling me that the power went out twice this week during high winds, which may have also caused surges, so I suppose that could have contributed to the problem, and be why a large chunk of them suddenly fell into it so quickly.

Unfortunately that doesn't leave too many long term solutions.


ETC Rigging General Manager
Premium Member
Fight Leukemia
Departed Member
Based on the info posted, I would suspect either something power related or heat related.

Power: Have an electrician look for loose feed and load lugs in the power panel. You'd surprised how often this happens, especially in older buildings, as wire tends to both hot and cold flow under screws and pressure plates. I had occasional flickering in my house a few years back, and it turns out it was loose feed lugs in the power meter box, on the power company side, last terminated and checked in 1974. Retorque every power screw from feed to outlet.

Have the power company tell you why there were flickering and outage issues with the feed. I once ran a theatre in NC that had feed flicker issues whenever the wind would pick up and the solution was to trim the trees that were touching to 7.2kV lines out back. All the issues went away as we were no longer trying to ground the high voltage feed.

Heat: Make sure these packs are mounted correctly and with enough air around them. If they are mounted flat and over top of a tungsten fixture, move it. It is possible that these are heat failing and it is also possible that once it starts, it may never completely recover.

I think you have sufficiently ruled out the console, data splitter and fixtures. I do still worry about 3-pin cable, even though you stated it is not mic cable, as it almost always is mic cable.

Agreed, Terminate all DMX runs. Self-terminating or not, do it, so that there is no doubt. Then make sure that the main power supply checks out and that there are no issues with it. Also make sure that you are not pulling more power per dimmer than the dimmer can handle. I doubt that that is the issue, but worth a look. Good Luck

Users who are viewing this thread