August 10

by David

One of the most crushing feelings you can encounter when working with lighting comes when things don’t work right!  

The uncertainty of where the problem is, coupled with a little confusion can make things really tough.

If you’ve never encountered a DMX problem before, be prepared to be a little confused.

On the surface, DMX problems can see very mystical and difficult to understand or troubleshoot.  

However, with a few tricks, it can be simple to diagnose and fix your DMX issues pretty quickly.

Symptoms

Most often, DMX problems are exhibited by:

  • The fixture is not responding to data (but it has good power)
  • Flickering, flashing, or uncontrolled changes to the light.
  • The fixture working “mostly right”, or has some control but not all functions of the light work correctly.

To make things worse, the “DMX” indicator light on the back of many lights isn’t really helpful either. While it’s a sign that there is some sort of DMX-like signal present, it can be on when there is not good data or can be off when there is good data!

This is where things get tricky…

Fixing Your DMX Problems

Step 1: Check Your Console and Fixture Settings

LED DMX Fixtures

The first step in finding a DMX problem is to check your console’s patch and the fixture’s modes/addresses.

Also, ensure that the console’s Grand Master and any other masters are where they should be.  If your console has an “output” screen that you can view, pop that up and check it as well.

Make sure that everything matches up the way that it is supposed to, and that it’s all plugged into the proper universes.

Then, whip out the manuals for your fixtures to be sure the modes are set right – if I fixture is supposed to be in 4 channel mode, but it’s actually in 7 channel mode, then you’re going to have problems!

A wrong mode setting can be particularly difficult to diagnose from afar because the light may be working “mostly” right. Some modes can be very similar and cause you to believe that the fixture was working and then started “acting up”, but the truth is, it was never fully right!

If you’ve had your rig setup for a while and not changed anything, then you can skip this step and move forward to check your cables and connections…

Step 2: Check Your Cables

If you are using microphone cables to connect your lights instead of DMX cables, this is likely the source of your problems! While microphone cables can work, they are not recommended, and over time WILL give you problems – click here to read my full article on using microphone cables for DMX lighting!

Once you’ve verified that, there are a few more tricks you can use to troubleshoot this DMX problem.

Active DMX for Testing:

The first thing I like to do is to give my fixtures some active DMX, so I can see when things stop working.   This will show me immediately which lights are responding and which ones aren’t.

LED moving lights on drape

Choose a chase or FX that is fast enough that you can track it and see when things become problematic, but slow enough that it doesn’t drive you nuts!

I like to run a static color with a chase in a different color across all of my fixtures, and I usually run it at about 25% intensity.

This gives me enough light to see what’s happening, but not too much that I’m blinded.  It also gives me a quick chance to check that the lights are in the correct addresses and placed in the proper places.

As I mentioned above, the DMX indicator lights on fixtures aren’t always 100% accurate, and that is why I run a chase across the fixtures – to make sure they are actively responding to data.

Then, do a quick walk through the problem area of your lighting rig and make sure nothing got unplugged or loose.

Is the problem with just 1 fixture, or many?

If it’s just 1 fixture, unplug it from DMX and try a straight “home-run” directly from the console.

Plug in only that fixture to the DMX and see if it works. If it doesn’t, re-verify the mode and address settings, then skip to the next section of this article!

After that, begin unplugging fixtures from DMX, beginning with the last fixture in the chain.

When the problem stops, replace the last cable that you unplugged – but don’t mark it as bad yet!   The next thing to do is to re-connect all the cables and see if the problem stays away.

If you touch a cable and everything begins to work again, try gently wiggling the jacks where the cable is plugged into the lights and also the cable itself – it may then present itself as a bad cable or as a bad connection in the fixture’s jack!

By re-connecting all the fixtures, starting at the problem, you are also able to see if/when the DMX gets too weak from having too many fixtures connected.  

You’ll soon know if the cable was bad or not! As we talked about in “How to Wire DMX”, it’s a good habit to limit each run of DMX to around 16 fixtures so that your signal is nice and strong!

[thrive_custom_box title=”What About DMX Terminators?” style=”dark” type=”color” color=”#99d6ff” border=””]

DMX terminators are mentioned in about every fixture manual as well as the DMX specification. So, why don’t I mention them often here?

Truth be told, I have spent a lot of time experimenting with terminators and talking with other industry professionals who have done so as well. What we have found is that while they do sometimes solve the problem, they also can cause other problems.

The explaination of that behavior from the engineers of the industry is that the system did not have DMX implemented correctly from the beginning. Here’s my take: you can try using a terminator when you have a DMX problem. Sometimes it will fix it, sometimes it will not. But I don’t recommend using them unless you do have a problem that you can’t resolve from these other steps. [/thrive_custom_box]

Step 3: When the Problem is the Fixture

Lighting Fixtures

It’s not just bad cables that cause DMX problems – fixtures with wrong settings or failing electronics can cause problems too!

If the above steps didn’t work, try skipping the fixture that seems to be in the problem spot of the chain. Always verify that the problem fixture is set to the correct mode and address. (Have I said that enough, already?)

Stand-Alone Modes

Some fixtures have stand-alone modes that shoot out DMX to other fixtures to control them in a master/slave mode, and we don’t want any of this on if we are using DMX!

If you’ve checked those parameters, but the problem still exists, then you’ve likely got a problem fixture.  

“Problem Fixture”

At this point, you can try to plug just that fixture straight into the console and see if it’ll respond.  

If it does, you can run in its own output from your DMX splitter and run it until it dies (which it likely will with time, as the DMX electronics inside are probably going).

Having its own run out of the DMX splitter will also isolate the light from sending any bad DMX to other fixtures, which is a plus if you were having that issue.

If the fixture in question does completely stop working with DMX, you can always try to contact the manufacturer to get it repaired – cheaper fixtures may not be repairable for a reasonable cost, but it never hurts to ask!

While it is rare that a console could be outputting bad data, it could happen.

Step 4: Could it Be The Console?

Use a PC-based console like Onyx to test your lights if needed.

In the steps above, we verified that our lights and console were set to the same DMX addresses, universes, and fixture modes.

But, you still could have an issue with the console.

If everything else checks out, try re-patching your console’s universe to a different output. Then, try a different console or use a PC to test your lights using an Art-Net or sACN node, which is a great tool to have around as a backup or for testing!

Conclusion:

When you follow the steps above, you will be able to isolate your problem and decide how to best move forward. I truly hope that this article has been helpful to you if you have landed here with DMX problems!

At the end of the day, what we love about DMX is that it is simple to use, and can be simple to keep working as well. Be sure to check out the other articles here on Learn Stage Lighting as well as Learn Stage Lighting Labs!

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