The strangest issue I've encountered in my 8 years of experience...

My company recently installed a small LED rig in a grammar school auditorium. We left the 10 conventional dimmers and added 6 Elation DLED 60 Tri strips, 10 Elation EPar QW, and 7 Elation Quad Par. Each fixture model has a dedicated and terminated line off the opto split.

For some reason there is this intermittent flash that occurs over channels not in use. I hooked up my handy dandy Swisson XMT-350 and noticed there is a dip in the bitrate every time it flashes. It looks like a steady 68 Hz, then a drop to 66 Hz, a flash of the rig (sometimes the whole rig, sometimes 1 line off split, sometimes just 2 fixtures), then back to a happy 68HZ.

Have any of you guys and gals come across anything like this? What could I possibly try to resolve it, keeping in mind I've tried all the normal troubleshooting tricks. I've changed cables, opto, consoles, and fixtures...

Now the school year has started and I'll feel terrible if the rig flashes throughout the entire first production of the drama club. The only suggestion I can make anymore is getting an instant replay to play a thunder track after each flash.

Thank you for any help you're able to provide!
 
What type of board/controller are you using? Is it always the same groups of fixtures or just random fixtures?

Here are three things I can think of...

1. One of your light fixtures is in some kind of master mode where it is sending its own DMX out of the pass through port in an attempt to control other lights, and this DMX signal is battling with signal from your board.
2. When an opto-splitter goes bad it does this sort of thing.
3. I once had a Leprecon board (an old LP-1524) that would only send out DMX data for the channels you had patched. The rest of the channels would have a mind of their own. My solution was to patch channel 512 somewhere on the board (even though it was not in use) and that seemed to make it send out DMX data as 0 for all the channels in between and solved the problem.
 
Thanks for the quick response! I currently have a Leviton N7532 in the room, but thinking the console was the problem, I've also brought in my Leperchaun LP-1636 and my Avo Pearl. With the pearl it flashed far less often, but was still present. I also thought that a fixture was possibly in master mode as well, but upon further inspection couldn't find one. And your opto idea is also a solid one, but unfortunately the flash still occurs even with no opto-split in line. When I go back to the venue I'll try patching channel 512 on the console and I'll let you know what happens. Thanks again!
 
With what you've said, I would try the patch thing, and also another thing to consider is your DMX cable. I'm going to be that guy and say to make sure you are using twisted pair DMX cable and not mic line or general signal wire. Most of the time you can skirt by with mic line, but it is more susceptible to interference from everything, especially with longer runs. If you have any long DMX runs bundled with A/C power or even a wifi router antenna placed near a cable, that could also be the culprit - especially if the cable is not twisted pair.
 
generally a dmx timing fault, I usually put in a dmx merger, which is not actually used as a merger but stabilizes the system cheaply, slowing down the rate will often fix it.
 
... I hooked up my handy dandy Swisson XMT-350 and noticed there is a dip in the bitrate every time it flashes. It looks like a steady 68 Hz, then a drop to 66 Hz, a flash of the rig (sometimes the whole rig, sometimes 1 line off split, sometimes just 2 fixtures), then back to a happy 68HZ. ...
I'm confused by this, as I thought DMX512 had a maximum refresh rate of 44 Hz.
Doug Fleenor Design also has their DMX decelerator on the market also, it's probably cheaper too.
Link to DFD product. One would hope you could find one to borrow in New Orleans, to test before purchase. There's also the device ESI DecaBox – ‘DMX Slowdowner’ » Engineering Solutions Inc from this thread: http://www.controlbooth.com/forums/...here-guys-jands-vista-chauvet-colorstrip.html .
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Thanks for the reference to the DMX DECELERATOR. I am biased, of course.

I hear this problem description more and more. While I'm not in front of the problem with all my test gear, it has all the right symptoms to be a DMX timing issue. More specifically, the fixtures that are flashing are probably not DMX-compliant. They can not cope with the in-spec timing being produced by your control system. You have already taken many of the troubleshooting steps I would recommend such as simplifying the system, changing cables, etc.

The DMX DECELERATOR was created specifically to remedy this situation. It will reliably accept any DMX signal (and some non-compliant variants). It opto-isolates the output and re-times the signal using "relaxed" timing parameters which the non-compliant fixtures seem to be able to digest. It has a list price of $200 and can be found for less through our dealers. More information is at: DMX Decelerator .

Sorry for being an ad, but it sounds like this is the right solution for the issue.
 
this is the merger I found by accident solved this same problem on 3 separate occasions, those in Europe may find it easier to source this than the excellent Doug Fleenor unit, I never travel without one now.What strikes me as strange is that a system has been stable for up to 3 years then developed these symptoms but adding this unit solves all the issues, I even used it as a merger once.
DMX Merge / DMX Gear / Lightcontrollers / Showtec / Highlite
 
Thank you everyone for your input. It looks like I have a few different things to try here. As soon as I can get into the venue and do some more troubleshooting I'll let you know how it goes. Thanks again!
 

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