Follow the points within this article to work on one fixture at a time, starting with the first fault in the DMX chain and then working backwards away from the DMX source. Once an issue is resolved, repeat the process until all fixtures are working correctly.


If all fixtures are affected (including the first fixture), this will likely be an issue with the cable between the device and the first fixture.


The DMX standard states that you can chain a maximum of 32 fixtures, this is to make sure the integrity of the data is kept. This can be maintained using a DMX Splitter.  If you are running long chains of fixtures, break up the chain into smaller groups to see if the issue still occurs. If the issue doesn’t occur after breaking up the chain into smaller lengths, increase the number of fixtures connected a section at a time. If the issue comes back, then the DMX signal has likely degraded too much. Consider using a DMX Splitter, which would regenerate the DMX signal and allow for multiple chains of up to 32 fixtures.




Not Functioning Correctly

No Output



If the issue occurs halfway down the DMX chain, bypass the previous fixture by connecting the DMX IN and DMX OUT connectors together.

  • Resolved: The previous fixture is may have a fault with the DMX Output, therefore move the previous fixture to the end of the DMX chain, or use a DMX Splitter to start a new DMX chain, starting with the affected fixture.
  • Not Resolved: The previous fixture is unlikely to be the issue. Connect the fixture directly to the DMX source (bypassing all other fixtures/infrastructure).
    • Resolved: Issue caused by a DMX Limitation or fixtures/infrastructure in the chain prior to this fixture.
    • Not Resolved: If DMX source is known to be good – Issue caused by a fault with the fixture or fixture’s address, mode, or settings.




Fixture Settings


Addressing: If the start address of the fixture doesn’t match the address in the software, then the channels being sent will not control that fixture correctly.


Mode: Some fixtures have multiple modes, enabling different levels of control. If the fixture is supposed to be in 4 channel mode but is actually in 7 channel mode, then you’re going to have problems! A wrong mode will normally look as if the device is partially working. Depending on the start address of the next fixture, you might see a channel overlap where one channel controls more than one fixture in some way.


Other: Some fixtures also feature additional features such as Master / Slave mode, Sound Activation Mode, Preset Mode, Automatic Mode, and Standalone Mode. It is important to make sure that this is off, and the device is set to its DMX channel Mode to allow for DMX control of the fixture via the DMX ports. If the fixture has a factory reset, you could set the fixture back to its defaults. This could flush out any settings that are set on the device that you are unable to locate.


  • Ensure that the settings match between the Fixture and controller. Follow refer to the fixture manufacturer’s user manual.
  • If an identical fixture is working correctly, copy the settings to match the fixture that is working.





It's important to make sure that all fixtures receive adequate power.

If the fixture is not receiving power, it could also be a blown fuse in either the electrical cupboard, within the fixture, within the plug or within the extension lead.

Many modern fixtures have a power link feature, meaning you can daisy chain power from one fixture to another. If you are using this, check the fixture’s user manual to see the power draw per fixture and that the number of fixtures linked isn’t the cause of this issue.





It is important to make sure that your DMX output device is connected correctly.

  • eDMX (Art-Net/sACN): Are you able to access the web interface/ping the node from the controller?
  • DMX USB device: Can your software see your device, is the output enabled?




Grand Master / BO

Some software has a built in Grand Master or Black Out mode. Depending on the software this might:

  • Prevent any output at all (all values at 0),
  • Only affect the Dimmer (or Colour values if the fixture doesn’t have a dimmer). In this case you might hear or see other parameters (gobo / Pan/Tilt) change but no light output.

Please ensure that the Grand Master (and any potential Sub-Masters) are at full, and any Black Out mode is off.




LED Status

Status LEDs on the Device can provide you with valuable information regarding what the Device is currently doing.

As there are some differences in terms of Status LED functionality from Device to Device, please view the specific Device's User Manual or Knowledge Base articles.




DMX Cable

DMX is a bi-directional digital signal which sends control data through the cable using electrical pulses (square wave). The DMX standard states that the cable must have an impedance of 120Ohms. It is important that only cable of this impedance that is specifically labelled for the use of DMX is used (not audio XLR’s).


When shopping for DMX cables, if it is labelled DMX Cable, then it should meet the specification. Label your DMX cables to help distinguish them from audio cables.

Using any other cable (for example microphone cable) which doesn’t meet the electrical characteristics (impedance & capacitance) as the required specification can cause intermittent errors (strobing / flicking) or irregular operation (loss of signal).


A fault can also occur with a cable if coiled improperly, or if a pin has become loose in the connector. If you suspect a faulty cable or a non-compliant cable is being used, then we recommend that the cable is tested.


To test DMX cables, we recommend the use of a DMX cable tester, if you do not have one to hand, you could use the following steps:

  1. Disconnect the suspected faulty DMX cable (the cable prior to the first fixture with an issue in the chain).
  2. Switch the suspected faulty DMX cable with the DMX cable from between two fixtures that are working correctly.
    • If the fixtures that had previously been working correctly display any faults, then the DMX cable is likely to be faulty.
    • If no fault is found, then the DMX cable is unlikely to be faulty.




New Show

There might be a setting within your show file that is causing the issue.

To rule out any strange issues with the show file settings, create a new show file and patch one fixture which you didn’t have control of and see if you have access to it.




Uninstall / Reinstall the software

There might be a setting within your software that is causing the issue.

To rule out any installation/setting issues with your chosen software, uninstall and reinstall the software - normally this process would reset the software settings.

It is recommended to use the latest version of the software that the developer has released.




Alternative Software

There might be a compatibility issue between the software and the device, or a compatibility issue between the software and your fixture.

It is worth checking with another piece of software to see if the issue is isolated to your software.

We would recommend using QLC+ for testing, as it is simple to use. For example, set the Device or Protocol to output within Inputs/Outputs and then use the top row of faders in ‘Simple Desk’ to control each channel.





  • eDMX (Art-Net/sACN): Are you able to access the web interface/ping the node from the controller?
  • DMX USB device: On a rare occasion the network settings on a computer can block the output from a device. Disable all network ports on your computer.




Frame Rate

It is possible that your lights don't support full refresh rates of DMX (40 fps and above).

Some consoles/software provide the ability to limit the refresh rate being outputted from the console/software. You can also limit the refresh rate on the hardware on most of our Devices. 

  • Open DMX USB: The frame rate is set to 40fps. The DMX signal is generated by the PC, this means that some parameters (Break length, MAB length, inter-byte time) of the DMX signal can vary from frame to frame (depending on the computers CPU load). These variations are perfectly legal under the DMX512 protocol, although some DMX devices do not like these timing variations and display strange behaviour. If you are experiencing issues with flickering with your OPEN DMX USB, then it might be worth looking at the DMX USB Pro or DMX USB Pro MK2 as these devices do all the processing on-board— meaning that the frame rate, Break length, MAB length, can be set for your fixtures and will always be consistent.




DMX Terminator

A DMX terminator is a 120-ohm resistor that terminates the DMX signal. If the DMX signal reaches the end of the lighting run and isn’t terminated, the signal can bounce back which will cause interference and lead to flickering lights and loss of control.

Connect a DMX terminator to the DMX OUT at the very last fixture in the chain which terminates the signal.





Some fixtures follow the previous USITT DMX512/1990 DMX standard, which doesn’t support RDM (Remote Device Management) - part of the USITT DMX512-A standard of today. These fixtures can sometimes behave erratically when they receive DMX data with RDM, causing flickering.

Our Devices are split between supporting either USITT DMX512/1990 DMX standard (no RDM) and USITT DMX512-A standard (with RDM). Please see the specific Device's User Manual and Knowledge Base.

With our DMX to USB products:

  • Open DMX USB only supports the USITT DMX512/1990 standard, therefore this wouldn’t be the cause of the flicker.
  • DMX USB Pro has two different firmware versions. One supports USITT DMX512/1990 DMX standard (RDM disabled) and the other USITT DMX512-A standard (RDM enabled).
  • ·       DMX USB Pro Mk2 supports USITT DMX512-A standard and RDM can't be disabled. 




Merge Mode

Merging can also cause flicking, if a device receives more DMX universes than it is expecting to handle then it can cause flickering. Some of our devices can merge DMX Universes. 

  • Merging might be disabled, please enable Merging 
  • Only two sources are supported for merging, more than two could result in flicker
  • ·       Sources cannot originate from the same IP address