Control/Dimming - Help- Wild DMX??

[jmac]

Starting tech week for second show with new Strand Classic Palette console. Connected to Leprecon VX-48 dimmer rack plus 5 Leprecon ULD dimmer packs. All lights are under control, but we have continuous but irregular lights blinking on and off (channels on low will surge up and down, and channels off will come on and off). Serious annoyance... Sometimes, it seems to hit a few (3-4) consecutive channels in a row, almost like a quick low level channel check, and then goes to another group.

When a channel is up at or near full, it seems to be unaffected.

When DMX cable is unplugged at console, problem stops. DMX line runs from console to DRk, and out of DRk to splitter which feeds the 5 dimmer packs, daisy chained. Two other feeds go to scroller power supplies, but this issue showed up before they were connected to system. I put DMX terminator on last dimmer pack on string, and no change.

Changed DMX "flavor" setting on console to different frequencies; maybe affected a bit, but couldn't resolve problem.

I'm new to the game, and don't really know what to do next. Seems like console is sending out random/stray signals?? Problem with console, DMX configuration, or splitter, or...??

Any ideas or troubleshooting tips? Thanks!

[theILLUMINATEDfrog]

I'm not an expert at troubleshooting DMX issues, but I have managed to solve all of my issues without losing too much hair...

1st, though obvious, make sure you haven't overloaded any of your circuits or packs...

2nd, try physically looping your packs instead of terminating the line... ideally termination should do the same thing, but maybe due to bad resistors, etc. Ive noticed loops sometimes work... "better?".... or at least at times when terminators prove bad.

3rd, check the profiles and addressing on all of your dimmers, power supplies, and scrollers.

[DCATTechie]

Kind of a shot in the dark here as I'm not a DMX expert. Did you try changing the DMX rate on the console, or is that what you meant by adjusting the "flavor"?

If you have another splitter at your disposal, try swapping them out and see if that resolves the problem.

Also, are the channels with the issues physical desk channels with faders or are they virtual console channels only accessible by the keypad?

[JD]

You need to use a "divide and conquer" strategy with these problems. If practical, move the board near the dimmers and start by using a short DMX cable terminated after looping through one rack. Make sure that your board ground and dimmer ground are solid to each other. If all works well, keep adding components until the problem reappears. Some possible causes:
1) Grounding issues between racks, board, and other components creating enough noise to disrupt system.
2) Over or under termination. If you are using a splitter/buffer/isolator, each output needs its own termination.
3) Splitter/ buffer failure.
4) Bad cable run and /or near a strong noise source.
5) Line driver on DMX board output failed or weak.
6) Failed DMX input on any rack or other device is loading the data line down.

There are other possibilities, but start with these.

[jmac]

Thanks for the replies. To answer some questions- No circuits are overloaded, most are 750W or 1KW fixture on 2.4 KW dimmer. Addresses are all ok, as control channels all work. Yes, adjusting DMX "flavor" on console does change the DMX speed. Some channels are recorded to submasters individually, but mostly in groups.

Not sure how to check for grounding issues. Console power is taken off DRk circuit breaker (same circuit powers splitter also).

Isolating pieces seems best (at least easiest for me) idea. I guess I will disconnect all but console to DRk and see what that shows. If good, I can then add DPk's one at a time. This may show bad device or cable. I can also delete the splitter, and daisy chain all devices with single terminator at end. I also have a pocket console, so I can substitute that for the console and see what happens with that....

Any other ideas appreciated. Thanks.

[derekleffew]

Originally Posted by theILLUMINATEDfrog

...2nd, try physically looping your packs instead of terminating the line... ideally termination should do the same thing, but maybe due to bad resistors, etc. Ive noticed loops sometimes work... "better?".... or at least at times when terminators prove bad. ...

Can you further expound on this "looping" methodology?

Originally Posted by jmac

...I also have a pocket console, so I can substitute that for the console and see what happens with that. ...

YES. Of course start by swapping consoles, as it's the easiest (to test, not to resolve).