Dmx signal issue when switching boards

Kozak

Member
Joined
Sep 11, 2015
Location
California, USA
Hello all!
I've just got done doing lighting for an event at my church, and something is bugging me. I'll keep is short and to the point: (maybe not)

We rented a fancy board (jands vista s3) and fancy moving lights, and we used the permanently installed lights in the venue. We plugged into the existing Dmx input to control the conventional lights (venue lights) using a separate universe, ran a 100 foot cable from board to input.

Problem 1:
Dmx cable faulty (or too long? ), lights flickered, but I still had control of what I needed...

Main problem:
Issue arises when I switch back from jands s3 to the etc express. (By the way: It worked perfectly when I showed up and tested if the light breakers were on). When I plug the Dmx lead back into the board, after I was done with my show, the lights didn't respond to it. I turned the board on and off, but still got no response from the lights. I assumed that there maybe still be some interference because of the faulty cable I used before, so i thought there may have been a signal still jumping around in the dimmers or something. (Btw, it still didn't work even when I turned the dimmer rack breakers Off and on.)

Then I thought there was a connection issue between the cable's pins and the boards connector, so I lightly touched the pins with my finger, then I plugged it back into the board and it worked perfectly.


Question 1:
How bad is it that I put my finger on the Dmx lead? Can a short happen this way (because of static or anything else)? (I took a lighting class recently, and this was never mentioned, so I'm pretty sure it's harmless?)

Question 2:
How likely is it that the jands lighting board, or the faulty cable could somehow cause the house setup to react this way, because of signal interference?


Thank you for any input.
 

Thetechmanmac

Active Member
Joined
Sep 1, 2015
Location
Northeastern NC
Chances are the DMX module in the express could have something wrong with it. And have never had a problem touching connector pins in my experience.

Try everything with a cable you know works and see it that helps.
 

petercav17

Active Member
Fight Leukemia
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Nov 17, 2014
Location
Philadelphia
As to problem #1, were you using proper DMX cable? Or were you using 3 pin audio cable? Using 100' of audio cable could cause a flicker. Also, not sure how the rack has its DMX hooked up, but if termination is a possibility, make sure you do that as there could be a signal reflection in the line.

Q1: As long as you don't emit electricity through your finger, you're fine. You touched the male end of the line, meaning that there was nothing to short since there was no supply of signal. You just absorbed anything in the line.

However, this makes me think that termination would be the problem here because when you temporarily "terminated" the line it began to work again. (A terminator is just a resistor between the two data pins, and your finger acted as a resistor in this case).

Q2: The only way that I could see the faulty cable or the jands desk causing damage to the house system is if the cable had swapped pins, which wouldn't make sense since you had control of the lights. So not likely.

When you went to reconnect the DMX back to the express, did you plug it into the right universe output?
Also, what type of dimmer rack are you using and is there anything else besides that rack on the house DMX line?
 

Kozak

Member
Joined
Sep 11, 2015
Location
California, USA
Thanks for your response.

We used 3-pin DMX cables provided by the rental company.. they did seem like they've lived past their glory days since they were falling apart at the connectors. Also, we used converters for the board. 5 to 3, 100' cable, then 3 to 5 for the conventional lights hookup, the ones that were flickering..

Also, I am sure i plugged the dmx cable back into the right universe, and i even tried the other one, just in case, when the first one didnt work.

As for the dimmer rack, i dont know much about it.. it all worked fine until i introduced the rental equipment. I read DPI1212 on em.. (i think theyre by teatronics)
 
Last edited:

Thetechmanmac

Active Member
Joined
Sep 1, 2015
Location
Northeastern NC
Where do you have the express set up for your show now- is it where it usually is for regular church stuff or is it setup in a different place with different cabling? Could be for some ODD reason it doesn't like the turnarounds. But since the DMX cable sounds like it's in rough shape, that is most likely the culprit.
However, this makes me think that termination would be the problem here because when you temporarily "terminated" the line it began to work again.
This does sound like a possibility. See if you can pick up a DMX terminator and put it on the output of the dimmers.
 

JD

Well-Known Member
Joined
Jan 1, 2005
Location
North Wales PA
Beware 3 pin DMX cable! Could very well be DMX cable, but might be mic cable, which can cause problems.
100 feet should not be a problem. Also, as stated before, make sure you use a terminator at the end of the loop.
Some moving lights and dimmers have a switchable terminator built in. If there is more than one terminator in the system, it will greatly reduce the signal strength which can cause issues.
 

Kozak

Member
Joined
Sep 11, 2015
Location
California, USA
ok, but the main issue is when I unplug everything and plug back into the existing system.. Is it ever possible for there to be some sort of "ghost signal" still in the system that doesnt let the etc board send out its own / interferes with its signal? Why I am so concerned with this is that we are just renting the venue every week, and this issue has caused issues with their system, and it makes us look like we dont know what we are doing.. I'm not saying I am a pro, but I know when something is my fault, and when it isnt (or at least unintentionally my fault).. I try to leave everything in good working condition after I leave, and this has only become an issue in the last couple weeks that we used the rental equipment.
 

Kozak

Member
Joined
Sep 11, 2015
Location
California, USA
ok, but the main issue is when I unplug everything and plug back into the existing system.. Is it ever possible for there to be some sort of "ghost signal" still in the system that doesnt let the etc board send out its own / interferes with its signal? Why I am so concerned with this is that we are just renting the venue every week, and this issue has caused issues with their system, and it makes us look like we dont know what we are doing.. I'm not saying I am a pro, but I know when something is my fault, and when it isnt (or at least unintentionally my fault).. I try to leave everything in good working condition after I leave, and this has only become an issue in the last couple weeks that we used the rental equipment.
To clarify..
The existing system never has issues on its own, so, i dont think that its a signal termination issue on its own... But maybe a new system and bad cabling that throw the existing system out of whack.. Sorry if im repeating myself..
 

disc2slick

Active Member
Joined
Feb 11, 2004
Location
Key West, FL
To clarify..
The existing system never has issues on its own, so, i dont think that its a signal termination issue on its own... But maybe a new system and bad cabling that throw the existing system out of whack.. Sorry if im repeating myself..
I would be shocked to find out that using a new desk and a bad cable did any sort of damage to the existing system. DMX can get weird sometimes but that would be some of the craziest weirdness ever if it were true. I'm pretty sure it didn't have anything to do the with the Jands console or the bad cable.

My guess is that either the house cable that plugs into the express is on it's way out, or the dmx output on the desk is on it's way out. My bet would be that there is a loose connection somewhere that works only if the cable it plugged in EXACTLY right. So when you 'fixed it' by touching the pins (which definitely did no damage to the system), it was probably more just that you unplugged and replugged that did the trick.

Like someone else mentioned try it again with a cable you know works. When it is plugged in and working I would GENTLY wiggle the connector plugged into the back of the console and see if it cuts out.
 

Les

Well-Known Member
Joined
Feb 24, 2004
Location
DFW, Tx.
Is it ever possible for there to be some sort of "ghost signal" still in the system that doesnt let the etc board send out its own / interferes with its signal?
No there isn't. If there's nothing transmitting signal, there will be nothing in the lines. Additionally, devices are always "listening" for updated information (which can happen at a rate of up to 44 packets per second). It's not like plumbing where you can get air in the pipes or something like that.

My bet is a bad cable - possibly the one between the wall and the console.
 

Kozak

Member
Joined
Sep 11, 2015
Location
California, USA
thanks for all your help, everyone! I am left with believing that its probably a cable/connector issue... but the venue reps contacted my superior and said it might have been some other issue.

I will see how things go from now on.. maybe ill try and get them to upgrade some things.