Cue problem/Possible DMX error?

[PDD]

Here's a quick problem I've been having:-

 

Using an ETC Express, via ETC Net, with Zero 88 demux to Strand STM and Act 6 dimmers.

 

Plotted a particular cue with a 3 minute fade time (very long sunset thing). Trouble is, as soon as the cue "goes", one channel flicks to zero then straight back up, then running the rest of the fade correctly.

 

This doesn't happen when the cue is given a much shorter time, such as 5 secs. Also, the level change doesn't show on the desk's monitor, so I'm hestitant to say it's a desk problem.

 

The channel in question is on one of the Act 6 dimmers, but I have changed to a different pack, so I would think that rules out a dimmer problem. Yes, the DMX is terminated at the pack.

 

So, any ideas? DMX error? Desk problem? Demux problem?

[merlin24]

HAve you tried taking the terminator out? Termination is a very grey area and is disputed widely as to whether you should use them or not.

 

Just a thought as I have in the past had DMX issues until the terminator was removed from the chain.

 

Andy

[gareth]

Hmm, sounds odd. Does it also exhibit this behaviour if you wheel (or 'slide', as you're using an Express!) the channel down very slowly? Or is it only when it's fading down during a cue?

 

Try softpatching another dimmer to that channel and see if it still does the same thing. Then softpatch the offending circuit to another desk channel and try it again.

[dbuckley]

Doesn't feel like a DMX problem, too reproducible and specific, feels like generated data, so it could be a desk bug, but since there are lots of Expresses out there doing fades every day its more likely to be something you've unwittingly programmed in... LTP maybe?? Only other thing with a brain is the demux, but that wouyld be an odd thing for a demux to do.

 

If you could buy / beg / steal / borrow an Artisitic Licence Microscope it has a channel flicker detector that would settle the argument.

 

And a three minute fade for a sunset - thats a very fast sunset :-) I just did a ten minuter for an afternoon fade...

[PDD]

HAve you tried taking the terminator out?

Done; but made no difference.

 

Does it also exhibit this behaviour if you wheel (or 'slide', as you're using an Express!) the channel down very slowly? Or is it only when it's fading down during a cue?

The individual channel seems fine; it only does the fault during the 3 min. fade cue.

 

Try softpatching another dimmer to that channel and see if it still does the same thing. Then softpatch the offending circuit to another desk channel and try it again.

Like that, the fault still occurs in both cases, which would normally say dimmer fault on that circuit, but as I've changed the packs I don't think this is likely (it seems therefore, to occur somewhere on the particular DMX channel). I've now moved the circuit to a different dimmer/DMX address, and soft patched that which seems to have got rid of the problem.

 

Doesn't feel like a DMX problem, too reproducible and specific, feels like generated data, so it could be a desk bug // Only other thing with a brain is the demux, but that wouyld be an odd thing for a demux to do.

I think it has to be desk or demux. As the offending channel is on a pack not our installed dimmers, I'm going to bypass the demux to see if I can narrow it down further.

 

Interestingly, this post seems similar.

 

[EDIT] Bypassed the demux and the fault still occured, even after swapping DMX cables etc, so it looks like a desk error on one particular DMX channel. Is that likely?

[dbuckley]

... so it looks like a desk error on one particular DMX channel. Is that likely?

 

On a fade, most unlikely, as it just a microprocessor outputing digital data, all the componenets are the same components for every channel... On manual control you can get dicky faders or buttons or the electronics behind them, but outside the control surface its pretty much all common.

[gareth]

To prove or disprove the 'faulty desk' theory, is there any way you can get hold of a different desk? If so, try programming and running exactly the same cue on another console. I've never heard of a desk developing a fault which manifests itself in this way before, but I guess it's not impossible.

[Brian]

Bypassed the demux and the fault still occured, even after swapping DMX cables etc, so it looks like a desk error on one particular DMX channel. Is that likely?

What DMX channel are we talking of here for the offending channel. And what are the two DMX channels either side of it doing?

[PDD]

To prove or disprove the 'faulty desk' theory, is there any way you can get hold of a different desk?

Yeah - that is my next step, albeit using our identical back-up console. As I've managed to get rid of the fault by using a different address dimmer, I'll try this at a later date. Surely, however unlikely (which it seems), as I've changed every other part of the system and the desk remains the only constant, therefore the fault must exist at the desk?

 

What DMX channel are we talking of here for the offending channel. And what are the two DMX channels either side of it doing?

#50 on universe 1. 49 and 51 are fine it seems, although 50 only plays up on that particular cue so it's difficult to tell if the fault exists anywhere else.

[gareth]

Yeah - that is my next step, albeit using our identical back-up console. As I've managed to get rid of the fault by using a different address dimmer, I'll try this at a later date. Surely, however unlikely (which it seems), as I've changed every other part of the system and the desk remains the only constant, therefore the fault must exist at the desk?

In the words of Sherlock Holmes, "When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth." ;)