Urgent!!!! DMX nearly destroyed my day

[Spyker]

ok.. so here's the set up-

 

-Moving heads, chroma banks, generics and 2 unique hazers.

 

-DMX splitter takes two separate lines in for chromas, and one with the movers on [im guessing the generics are fed in along the way up the DMX chain

 

-All heading towards a Grand MA ultralight.

 

Been having problems getting control, but this is only now and again. Had full control for two days on fit up and technical, then opening night.. go to power up and get into preset, I got Mac700's doing random stuff, parts of the chain not responding and some behaving perfectly normally. This happened again today just before we opened the house... I was striking lamps as the house was filling up!! I seemed to get it sorted by switching fixtures off and on again, reseting the board, pulling out DMX from the splitter and reinserting it, going into different splitter ports. Once I got it sorted the show ran well, with absolutely no problems [which makes me think its not some signal cabling problem]

 

The grid is powered up in phases rather than all at once, could this be affecting things? and is there a preferable order for power/splitter/board on?

 

Things ive checked: Modes on fixtures, DMX addresses, error notes on Full Access exit screen, DMX receiving lights on fixtures.

 

Any help/ ideas/ things to try would be gratefuly received.

 

Thanks!

[gherriott]

You seem to have tried all the initial troubleshooting checks...as yet I cannot think what it could be apart from maybe a problem in a cable somewhere that is intermittant? I would suggest though that you power up from the desk towards the rig...ie. desk, splitter, scrollers, macs etc. Just work your way along the DMX chain from the desk. This shouldn't normally make a difference, after you go past the splitter, but seeing as you have tried most other things...

 

Hope this sorts it for you!

[Spyker]

So do I!!! thanks for the msg though matey..

[Ben]

What buffer are you using?

[Spyker]

What buffer are you using?

 

 

its a pulsar splitter....

[DonkiDonki]

Are any/all of your DMX lines terminated?

 

I often find that a damaged or intermittent cable will be shown up for what it is when terminated.

Unterminated they seem to sit on that horrible "just about working/oops not working" state which seems a nightmare to diagnose.

(And despite some people claiming that "most DMX kit terminates itself" these days; I prefer to terminate each line myself)

 

I would also suggest putting a buffer/splitter before the dimmers. I have had issues in the past with various pieces of kit not liking to be on the same DMX chain. I never had time to get right to the bottom of it but I suspect not all DMX equipment behaves quite as it should; possibly something to do with in-compatible timing or such-like.

 

Highly recomended also, for general DMX toubleshooting; would be a gadget such as the Artistic Licence Micro-scope. Such devices can be used to monitor the DMX line, just send all 512 channels at a fixed value from the desk and then monitor each end of the chain. Anywhere that isn't a rock solid match to the desk output has a problem; then it's a simple case of working your way back to the desk 1 cable at a time.

 

(Personally, from the way your rig works sometimes but not others; I would hazard a guess that you have a damaged cable running near the mains supply for some other equipment which is not always on, Generics, Air-con, etc.)

[Kazeja]

Clutching at a straw, have you tried loading an earlier version of the show, assuming you've saved one?

[cedd]

I would also suggest putting a buffer/splitter before the dimmers. I have had issues in the past with various pieces of kit not liking to be on the same DMX chain. I never had time to get right to the bottom of it but I suspect not all DMX equipment behaves quite as it should; possibly something to do with in-compatible timing or such-like.

 

I've had this with Betapack 2's before. Again, we never quite sussed out what the problem was, only that everything downstream of them behaved very oddly.

 

Thinking aloud though, I suspect that this would lead to a fault all of the time, not intermittently, unless the problem is tied in to your power-on sequence.

[p.k.roberts]

The only time I've had a similar problem, I eventually tracked it down to one of the DMX lines having an intermittent connection to earth (some helpfull soul had put a staple through a cable!), but the symptoms were pretty much identical to those you describe. I just had to keep shortening the chain until the problem went away, then build it up again with known good components. Good luck! (I'm still hunting for the phantom stapler ........)

[David A]

If the shells of your plugs are connected to to pin 1 earth, then you can get earth loop problems, just like sound, except it's harder to detect because you can't hear it, it just shows up as an intermittent fault, losing the screen will also give you a similar intermittent.

[Biskit]

As a few others have suggested, make 100% sure all your cables are okay, and if possible, swop out each one for a known good one to check this. I had a similar issue a few years ago: a new install, using an existing Strand GSX desk. Normally everything okay, however occasionally (typically on a show night!) we would get random problems, flashing of odd channels, scrollers scrolling randomly, etc. It was worse with any desk other than the GSX.

 

Eventually we found the problem... a DMX link between two dimmers which had data- line making intermittent contact at one end at one end (dry soldering). It confused us for ages, because problems occurred both up and down stream of this particular cable. It was only when we systematically connected each DMX item in turn from the desk end and tested thoroughly that we narrowed it down to this link. Needless to say, an interesting comversation with the installers followed!

 

Incidentally, we still can't explain why the GSX was generally ok but not other desks... perhaps it has a more 'powerful' DMX output than some other desks?

 

HTH

 

Ben.

[dmxtothemax]

I had a simular problem with my DMX lights. it turned out to be faulty dip switchs on one of my lights. because DMX lights can be slaves or masters, they can if faulty be trying to master the other lights, with strange results if they are different lights with different DMX configurations. try removing one light at a time from the DMX lines, and see which one is the problem.

[Spyker]

Thanks to all you chaps for the advice! same problems today! and same result.. once it was up and working, it worked fine for the rest of the day. Ill try some of the things you suggested. Much appreciated , this was my first post- and its cool to talk to other people about lighting probs.. 9 times out of 10 as LD your the the only one in the venue who should have all the answers. Thanks again boys!

[martin b]

Just a comment for troubleshooting DMX-chains..

Many people starts in one end of the chain an goes forward taking one canle at a time, but actually the smartest in the long run, is to start by dividing the chain in two, by simply unplugging half way trough the chain, if the problem is till there, you know the fault is in the half that is till plugge in, and ju now divide this chain into two.. and that way you will qukly be able to find the cable/lamp that is faulty...

[SoLiEn]

Just a comment for troubleshooting DMX-chains..

Many people starts in one end of the chain an goes forward taking one canle at a time, but actually the smartest in the long run, is to start by dividing the chain in two, by simply unplugging half way trough the chain, if the problem is till there, you know the fault is in the half that is till plugge in, and ju now divide this chain into two.. and that way you will qukly be able to find the cable/lamp that is faulty...

 

That's actually a bloody good point, thankyou, never thought of it like that! Shall use that at work when the need arises!

 

Again all I can think of is a damaged cable really. would be good to hear the actual cause when it has been discovered!

 

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