DMX Flickering Issue with uPowerTek LED Drivers on CueCore2

[gregorku]

Setup (sports hall installation):
28× LED fixtures with uPowerTek BLD-xxx-x-MRU drivers (DMX/RDM)
Visual Productions CueCore2 (DMX A output)
Visual Productions B-Station2 (used for addressing with DMX memories, later connected via network; 3 units on a switch)
Wiring: 3-core DMX cable (DMX+, DMX−, GND)

Topology:
Fixtures are wired into two DMX branches, which are then merged together and connected to DMX A of the CueCore2.
During addressing, I connected both branches into the B-Station2 and used RDM to read driver information.

Configuration:
All fixtures were addressed, set to personality C, dimmer raised to 100%.
RDM was disabled after addressing.
B-Station2 panels are now connected via network (Art-Net/sACN through a switch).
CueCore2 is sending DMX A to the fixtures.

Problem:
Fixtures respond correctly to commands, but random units flicker occasionally (not all, not simultaneously).
If I disconnect the DMX cable from the CueCore2, the fixtures stay on without any flickering.

My questions:
Could the issue be caused by the topology (two branches merged into one “Y”), and should I instead use a proper opto-isolated DMX splitter?
Do I need a 120 Ω terminator on the last fixture of each branch (so two terminators total)?
Are there any recommended CueCore2 DMX timing settings (break, mark-after-break, refresh rate) for uPowerTek MRU drivers?
Should I keep RDM completely disabled during operation (and only enable it for service/configuration)?
Can anyone recommend a good, affordable DMX line tester (single-end) available in the EU that shows signal presence, line faults, and termination?

What I’ve tried so far:
Disabled RDM after addressing.
Tested both branches separately → still the same flicker.
Rewired both branches into a single CueCore2 DMX A output → still occasional flickering.

[Julien Levaufre]

The really first advice I can give you is to never do a Y connection with DMX.
As you said in your post you should use a Splitter, or you can output universe A of the CueCore2 on outputs A and B, this way you do not even need a splitter but you have 2 "clean" DMX lines.
 
Now to solve the flashing, you can try to use the "slow dmx" function in the CueCore2 settings, that will slow down the DMX frame rate from 40fps to 20fps.
If this doesn't solve the problem, it is probably that your cables are catching interferences.
Give a try to the 120 ohm caps at the end of each line, check that the DMX cable you are using has the right impedance and is shield, and check that the shield is connected to the ground of your connectors.
And then check that your DMX cable is running with some hight power cables, like AC power that would create interferences.

Good luck, it's always annoying to find the source of this kind of behaviour.

[gregorku]

Thanks a lot for your  reply! I was considering using the RdmSplitter (Terminal version) from Visual Productions to cleanly separate the two lines. Do you think this could be a good solution in my case?

[Julien Levaufre]

Our RdmSplitter is for sure a good solution to replace your Y connection.
But as I said previously if you only have 2 lines you can just use the second output of the CueCore to output the same univers. ( go to the settings page of the CueCore and change PORT B to universe A in the DMX block)

[gregorku]

We also tested running only one line (the other one disconnected), but the fixtures still flicker randomly in the same way.
So I’m not sure the Y-connection is the main cause of the problem.
It seems more likely that there is some interference or an issue with the grounding/loop in the wiring.

[Julien Levaufre]

yes this is probably the reason of the flickering, and it will be annoying to find...
So good luck on that.

But I would definitely remove the Y connection, even more knowing that you can replace it using the 2 outputs of the CueCore2.

[gregorku]

We followed your advice — removed the Y connection and used both outputs (A and B) of the CueCore2, each driving one clean DMX line.
Everything worked perfectly for about a week, with no flickering at all.

However, today the flickering came back again on some random fixtures.
Nothing in the setup was changed, so I suspect the issue might be related to grounding or interference in the cabling, rather than the DMX topology itself.

At the moment there are no 120 Ω terminators installed at the end of the lines, and the DMX connector shields are not bonded to the cabinet ground.
We’ll check both and also confirm that the “Slow DMX” setting is still active.
If the issue persists, I might try adding a Visual Productions RdmSplitter to fully isolate both lines.

Any other ideas or similar experiences would be very appreciated.

[Julien Levaufre]

The last thing would be to check if your DMX cables are not running too close of power cables...
Good luck,

[gregorku]

We’ve recently identified a new and quite interesting cause behind the flickering.
After the construction workers leave, they switch off the main power supply for the entire building.
When power is restored, all loads in the hall start up simultaneously — including heaters, grinders, and other heavy equipment.

During this phase, the lights flicker for about 10–15 minutes, and then everything stabilizes and works perfectly.

This clearly points to voltage sags, inrush currents, and electrical noise during the building’s power-up cycle.
It’s likely that the uPowerTek DMX drivers experience temporary undervoltage or data sync issues while the CueCore2 and network devices are still booting.

We have also physically separated the DMX cables from power cables as much as possible, to minimize electromagnetic interference.
After that, the system became slightly more stable, though the flicker still appears during the heavy startup phase.

[Julien Levaufre]

I am happy to see that you find the reason of the flickering.
Good luck to solve the last issues.