DMX noise - console, lights, or cables?

joat222

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Joined
Mar 14, 2007
Hi all,

I am having a problem with DMX signal noise seemingly. I am running a Leviton Innovator 24/48 with three universes connected to it, one of them having three Studio Colors and 2 Studio Spots on the line.

When going through my show, after about 1.5 hrs, I will start seeing some erratic behavior on my moving lights. Lights will flicker, jitter, or even change color. It seems to get worse as time passes as well. All the lights spaz out at the same time. I have tried changing ports on my board, changing cables, connecting one light at a time to see if a particular problem light or cable can be identified, and no pattern seems to be emerging. My dmx run is terminated as well.

I have a huge show this weekend so this problem needs to be resolved quick, so any responses I receive will be more than appreciated. My next course of action is going to try an optosplitter to increase signal strength. One thing I did notice was when I shortened the dmx run length the problem subsided for a while, so I am thinking that the signal is just losing power over time. Hopefully the optosplitter will give me the power I need to keep it steady.

- kevin
 

gafftaper

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It sounds to me like you are doing everything right to trouble shoot it. Hopefully the optosplitter will give you a little boost and fix it.

The only other potential problem I noticed was you didn't mention your cable quality. Is it good DMX cable?
 

soundlight

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Shouldn't be an issue if you have the real deal DMX cable, but is the last fixture in each chain terminated?
 

stantonsound

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Feb 18, 2005
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Since this seems to only occur after about an hour and a half, it almost sounds like a temperature problem. I have heard of the internal controls of fixtures getting hot and causing problems. This could be the case on one of your fixtures, and it is sending out a corrupted signal on the output.


Granted, it is not as easy of a fix as a bad cable, nor is it as common. Since you have evidently tried all of the quick fixes, I brought this up. Check the cooling fans and internal temps of the fixtures as they are operating.
 

Van

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This might be a bit out there, but...... Since it's an issue that only seems to crop up after a period of on time, perhaps the issue is in a connector. When I first read this I envisioned a connector on an panel on the side of an ML the heat from it being on for a long time rises heats the panel and the XLR connector female receptcles expand with the heat and cause a loose connection, or at least a connection loose enough to build up capacitance enough to cause a reflection. Check your runs for other possible "hot spots" where a cable might be heating up.

I'm only throwing this out because as SL and Gaff just said it seems you are doing everything to diagnose the problem correctly.

Van's #1 DMX rule, Terminate, Terminate, Terminate. < it's really funny if you do it in a Dalek voice>
 

joat222

Member
Joined
Mar 14, 2007
Thank you all very much for your replies.

The problem was the worklights! Evidently they were causing some sort of electrical disturbance in the board and causing noise on the dmx signal. When I unplugged them the problem completely disappeared. I did notice that one of them had to be kind of shoved into the socket in order for it to turn on. I am so thankful that my friend had the idea to try unplugging them. Looks like the show can go on! Needless to say that I chucked those things in the trash...
 

Thomas

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Nov 2, 2005
Location
Durban, South Africa
You should check the power while you're at it- sometimes my MAC250's get crazy, and the first think I do is check the power- it's not DMX because we're all wireless :)

Someone in the office made a whole lot of DODGY cable- earth connected to live or live and neutral swapped around- things may work, but problems will show up sooner than later...

Heat may be an issue- it's possible that fixtures are running over or under powered, which has all sorts of kak effects on your gear. Pick up a simple multimeter and check what's coming out of your sockets- then adjust your fixtures to match as closely as possible- the manual will have instructions on this.
 

SHARYNF

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Sep 3, 2006
Another thing to look for is the shield in the cable being connected to the outside of the connector. Good practice is that this is NOT connected, and also with some of the connectors it is easy to have the shield touch the connector when you are pushing it back together under the slide on cover. This can cause all sorts of wierd problem where a small ground current is introduced into the system from connector that is not isolated and picks up the current from something it is resting on.

Sharyn
 

Chris15

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Someone in the office made a whole lot of DODGY cable- earth connected to live or live and neutral swapped around- things may work, but problems will show up sooner than later...
My question to you is why does this cable still exist? As I see it, there are two options with cable like that. The first is to fix it NOW. The second is to cut plug and socket off NOW. Otherwise, it might not be a light doing funny things next time, it might be a person. Sorry for the hijack.
 

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