Let’s Troubleshoot DMX Problems like this!
One of the most crushing feelings you can 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. Unlike a power problem, a DMX problem isn’t so simple to diagnose. However, with a few tricks, it can be simple to diagnose and fix your DMX issues pretty quickly.
Symptoms
When you’re having a DMX problem, some your lights may begin to flicker or stop working. However- this does not mean the problem is with the flickering lights OR their cables – the problem may be on the clear other side of the DMX chain! Or, perhaps you lose data completely – though this is likely just a unplugged cable.
Another symptom you may find is that certain lights may have gotten DMX data, only to drop it and be stuck in a color. All the while, the DMX indicator lights on the back of fixtures may be illuminated – while they’re helpful, they are also sometimes wrong when signal is weak! This is where things get tricky…
Fixing Your DMX Problems
Check Your Console and 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 a “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 in to 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!
If you’ve had your rig setup for awhile and not changed anything, then you can skip this step and move forward to checking your cables – the cause of most DMX issues!
Check Your Cables
Regardless of your DMX problem, there are a few tricks we can use to narrow it down.
The first thing I like to do is to give my fixtures some active DMX, so I can see when things stop working. Choose a chase 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 alluded to 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. After that, begin unplugging fixtures, 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! You shouldn’t make a habit of going over 16 fixtures in a DMX chain because the signal may get too weak.
When the Problem is the Fixture
While DMX problems are almost always due to a bad cable, bad fixtures can cause you problems as well.
So, if the above 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.
Some fixtures have stand-alone modes that shoot out DMX to other fixtures, causing a host of problems!
If you’ve checked those parameters, but the problem still exists, then you’ve likely got a 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 it’s own output from your opto-splitter and run it until it dies (which it likely will with time, as the DMX card is probably going).
Having it’s own run out of the opto-splitter will also isolate the light from sending any bad DMX to other fixtures, which is a plus. 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.
