Here's the problem.... Some Martin 518's I worked with recently (they're not mine, I program moving lights for someone else) had, what I can best describe as some 'fidget' problems. The mirror stepping was extremely choppy and many time when I would recall scenes, the positioning was extremely off.

The solution (possibly).... A phase reversing cable from the desk to fixture #1. This is the solution I've devised from my research on the problem. Has anyone ever had this problem before and/or tried this phase reversal solution?

I don't know when I will be working with these fixtures again, but if I know this solution will work, I will go ahead and make up a run of reversal cable.

I don't have nearly the experience that you do with this sort of thing, but are you sure that the ground is sound and that the shield is continuous through the entire cable? Is the same thing occurring in multiple fixtures? Is the cable properly terminated?

Assuming this isn't you, here's another person with a similar problem:

http://www.churchmedia.net/CMN/lighting-......18s.html

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I can't speak to the quality of the cabling ( I only programmed, didn't hang the rig) but I do know that the last fixture in the stream was terminated.

Unfortunately, the gig had so little time to load in and tech, that I didn't have much time to track which fixtures were spazzing out when. I do recall that at least 4 out of the 6 did it at some point that day.

I had read that thread at churchmedia.net. The problem is that it sounds like his issue was solved by adding a terminator, which we already had.

Man, and I thought I could come across as being really smart!

;)

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No.... I appreciate it! It's good to know that other people are on the same page and trying to help.

Hey Paul, dumb question time....I seem to remember we had a talk about DMX cable vs. XLR and "is it the same, would it work", that sort of thing. I don't recall what conclusions we came to but, your spazing 518's sort of rings a bell somewhere.
Anyway (here comes the dumb part)Because you didn't hang them, or do the cable run, could the person who did do the install put an XLR in the line by mistake.
I know it's unlikely but XLR and DMX are so much alike you never know....

Morgan

....or you could just hit them with a hammer.

I would also double check the terminator. Perhaps the resistor or wires are shorted out.

Each cable should be checked for continuity with a multimeter.


Kevin

DMX is (I hope) 5 pin, and XLR is (I hope) 3 pin.

As Kevin says, I'd check the terminator. Usually if it's a cable issue it doesn't work at all.
Those gremlin type problems are usually caused by "reflection" on the DMX line due to either no terminator, or an improperly terminated "end of the line".

I should know that. And that being the case, your right, if there was an XLR in the line I doubt it would work at all. My Bad.

Ms.M

No, wait I take it back...an XLR would work in a DMX line, just not well.

I maybe way off here but, DMX transmits at around 250kHz. XLR at something like 20Hz to 20kHz so a DMX signal would push an XLR way above it's range but it would carry. However, the impedance would also be different fom DMX to XLR. And when impedance meets non-matching impedance you get reflection. Happens in audio all the time sometimes just different brands of cable will have impedance trouble.

As for mixing XLR up with DMX, why not? A lot of moving lights have XLR 3-pin connectors for the control input. Don't know why but they do. Because of this it's not uncommon for people to use 3-pin to 5-pin adaptors on their DMX equipment. And very easy to pick up an XLR cable or 2 by mistake.

I'd still check for a misplaced XLR in the line or even a Y-splitter used somewhere. If the terminator is working it has to be a data reflection bouncing off of something.

...or, again, you could just hit it with a hammer.

Morgan

Something I've never understood - the DMX "standard" is 5-pin, but a large number of manufacturers still use 3-pin, including Chauvet and others. Is it a cost thing, or something else?

I assume that when she refers to the "range" of XLR, Ms. Morgan is referring to using stock XLR cables. I would think that using XLR connectors wouldn't be a problem, as long as standard DMX cable was used. Is this correct?

Yes, you can send DMX over a standard audio cable, and yes you can get 3 pin to 5 pin DMX adaptors.

Becaue you can doesn't mean you should. (some semi-pro fixtures are of a 3 pin variety, which is why they're called semi-pro).

The DMX protocol is published and available in many different places. If you try to improvise, you'll be chasing problems until 5 minutes before showtime, and likely dealing with them during the show as well.

I've switched to DMX over Ethernet, which is even more fun!

Plenty of non 'semipro' fixtures are still three pin....so I am not quite sure what silverking is speaking of. High End, Martin and various others still use three pin.

Kevin

I spoke with a buddy of mine about this... he used to be the maintenance supervisor for the moving lights on the Dave Matthews Band tours for many years and saw almost every kind of light out there. He said for the Martin 812s and 518s you DO need a phase reversing cable from the desk to fixture #1. For some reason, those fixtures use their own proprietary language that needs to be adapted from dmx by switching pins 2 and 3. Don't know why.... just does.

Martin certanly isn't semi-pro, so I do stand corrected.

I've done a "forced" five pin standard in my venues, currently configured to "DMX over powered ethernet".

IMHO, three pin DMX is an accident waiting to happen, always has been, and always will be.

Clear-Com, Audio Line-Level, Mic Level, Some Pyro control cables, all dangling around the stage looking like the three-pin DMX cable and all capable of frying your fixture.
I had a stage hand who plugged a 3 pin scroller control cable into a Clear-Com line (accidentally of course, which it always is).......everything was fine until the first person hit the "Call" button on their Clear-Com......

That's interesting. Everyone thinks they have a way to do it that is just a little bit better (read "proprietary").

Ok, that makes sense. If they are older 518's then you are correct, they are using Martin's own protocol. All recent Martin fixtures use DMX 512 now.

Kevin

P.S. Silverking...great story about DMX and Clear-Com...LOL

Its not that hard to do - just time consuming - I have a few in my inventory - although I no longer have a need - its always good to hold onto them. I am currently using highend colorspote and mac 2K fixtures.