HELP!!! Chamsys Magic Q PC DMX SCROLLERS POWER

[TupeloTechie]

Im not sure what to call this but I have quite a problem and need some help as soon as possible!

I am running a show off of the Chamsys Magic Q Pc with the Enttec Open DMX/USB. I am controling 4 scrollers and 21 old EDI dimmers that I believe were originally anologe and are now converted to DMX. Everything worked perfectly until I needed to plug in my laptop to the wall. The minute this happened all my scrollers began to go crazy and jitter back and forth in the middle of a color. I take out the cord and everything goes back to normal.

I am using old Chroma Q Scrollers and the lines are terminated back to the PSU. However there is no termination on the DMX itself as the wall box only has an input jack.

[Footer]

You need to terminate your last power supply, the DMX out on the power supply. You have each scroller string terminated, you must terminate the DMX string.

I assume you have the cheap DMX interface, the one with only one output? I want to say that thing uses a different chip then the full version and does not always send out full frames. I'm not sure on this though. What I believe is happening is your power supply is producing some weird voltages, probably on the 5v line in your PC. That is throwing off the DMX output somehow, who knows what is it exacly. Terminate your line, check you cables. Sounds to me though the problem is in your computer, but fix the DMX line first.

[soundman]

If you have an opto isolator I would insert that in the chain between the DMX out and the first device. This will determine if the problem is in the DMX signal or the voltage.

[n1ist]

The open dmx is just a simple usb-rs485 transceiver. It depends on the PC keeping up sending the data. Any activity on the PC can interrupt the data stream.

One other possibility - try using a powered USB hub. It may help clear up any power issues.
/mike

[David Ashton]

As everything works fine until you plug in the computer it is almost certain that the switch mode power supply is creating noise which is false triggering the scrollers.The possible answers are different power supply or as suggested usb hub or dmx booster or different computer.

[TupeloTechie]

well believe it or not everything was fixed by simply lifting the ground!

[Footer]

Originally Posted by TupeloTechie

well believe it or not everything was fixed by simply lifting the ground!

Not the best idea in the world. Does not surprise me that it fixed it, but still not a good idea. You now run the risk of completely losing your laptop if you have a short come down your DMX line.

[TimMiller]

You are not having a termination problem, you are getting a ground loop (just like you can get in audio, just in lighting world its in the form of everything freaking out). I would unplug the scrollers and start with the dimmers, if everything is ok, i would then move down the data stream swapping cables and checking connections until it was fixed.

[David Ashton]

On the same theme, some connectors have a link between the screen, [pin 1] and the case, this must not be connected, it is a major source of earth loop problems in dmx and audio, as it earths the signal at every fitting.