Moving Light Freakout - Terminator was the problem???

[Lotos]

Okay, so...

During our evening show tonight, one of my moving lights wigged right out... It had "twitched" a few times before, but today, it may as well have been in demo mode...
Needless to say, I had zero control from the console, and the only solution was to physically remove power from the posessed fixture.

Post-show, I take a lift up to figure out what happened, and in the midst of cable changing, a problem solving, I notice that whenever I remove the NEXT data cable in the path, the problem goes away...
In complete curiosity, I remove the terminator from the final light.

Problem solved.

Plug the terminator directly into the problem light... It starts dancing.
Remove the terminator, it responds the console as if it were fine.

Okay, now I'm confused.
I've run into my fair share of DMX issues in my career... But never one that removing a terminator fixed...

Thoughts? Comments? Questions?

 

[derekleffew]

See the thread https://www.controlbooth.com/threads/wacky-dmx-issues.8929/ , particularly:

...I would not totally discount a cable issue. Putting a terminator on a "one legged" DMX signal will make a seemingly "working" system break (of course, the system is actually already broken). ...

 

[Lotos]

See the thread http://www.controlbooth.com/forums/lighting-electrics/8929-wacky-dmx-issues.html , particularly:

Thanks for that Derek, I recall reading that post now... But of course, I needed your trigger to get there.
I'll look into this a little more heavily tomorrow.

 

[cbrandt]

I've also seen this problem occuring with other improper wiring methods. Systems with DMX Y cables and such, or using both outputs from a fixture with 3 and 5 pin (same thing as a Y) can trigger this with a terminator. I have some notoriously heavy data usage 48 channel dimmer racks that are just fine (that have in the individual dimmer packs cabled together with an unterminated length of Y cable internally), as long as you don't plug a terminator in. If you do, it is an instant show, with all the lamps randomly flashing.

 

[DavidNorth]

If you drop Data+ or Data- somewhere along the daisy-chained path of cables due to a broken conductor, and have a terminator in place, all the devices past the point of the break will not work correctly or at all. Seen it quite a few times and is a tricky one.

What happens here is that after the conductor break, the remaining data signal [D+ or D-] goes down to the end of the line, through the terminator and back up the other data line. This means that you no longer have correct differential data as D+ and D- are the same minus a little amplitude and a crazy amount of timing. So the light wigs out. When you remove the terminator, the light works fine because one of the data signals and data common are still in place and most receiver chips will still work with this.

[Edit by Mod.: See http://www.controlbooth.com/threads/dmx-out-from-etc-wall-jack-panels.37293/page-2#post-324290 , last scenario.]

A terminator at the end of line only causes problems if there are wiring issues, too many unit loads on the line or weak driver/receiver chips.

Hoping my suggestion helps.....

David

 

[Lotos]

If you drop Data+ or Data- somewhere along the daisy-chained path of cables due to a broken conductor, and have a terminator in place, all the devices past the point of the break will not work correctly or at all. Seen it quite a few times and is a tricky one.

What happens here is that after the conductor break, the remaining data signal [D+ or D-] goes down to the end of the line, through the terminator and back up the other data line. This means that you no longer have correct differential data as D+ and D- are the same minus a little amplitude and a crazy amount of timing. So the light wigs out. When you remove the terminator, the light works fine because one of the data signals and data common are still in place and most receiver chips will still work with this.

A terminator at the end of line only causes problems if there are wiring issues, too many unit loads on the line or weak driver/receiver chips.

Hoping my suggestion helps.....

David

Thanks David,

This, and Derek's post, have given me a decent point in the right direction.
The ideas presented here (Check all cables, Possible bad opto port, Too many units on chain) are all ones that had gone through my head to check for, but now I have a reason why!

It appears the receivers chips in these lights are fairly forgiving in general, as only ONE of the lights (3 units from the end of the chain) began experiencing mega-disco-party issues last night... But as I was problem-solving, just prior to realizing the terminator insanity, I did notice the final light in the chain twitch slightly out of the corner of my eye.

Thanks again folks


P.S. cbrandt: Don't worry, no Wye cables in use here.

 

[ejsandstrom]

I had this problem with some of my P5Rs. They would randomly wig out. After an exhaustive troubleshooting session, I sent them in for repair. Problem is gone now. So sometimes it can be the light.

ETA: We also had a problem when we started to get close to our fixture limit. I was at 22 fixtures on one of my universes, as soon as I added 23 (very cheap light) stuff started to freak out by the time I got to 28 it was like a disco. Everything was blinking and spinning and changing color.