Wacky DMX issue

[icewolf08]

Here is an interesting one. So, for the first time in 2 weeks of operation of the rig for the current show I started to have a wacky DMX issue. All of the DMX gear on one of my electrics just started to twitch. The electric is fed from one DMX line from an Opto-Splitter. There are two ETC Revolutions, an ICue on a SmartPower PSU, and 4 Chroma-Q Mk.II Scrollers on a Chroma-Q PSU. The chain goes: Opto>SmartPower (ICue)>Chroma-Q PSU>Rev>Rev. I didn't put a terminator in the last Rev as I have the ones with built in termination.

The odd thing is that the "twitch" only shows up after everything is powered up for a while. Also, it goes away when I hard reset the Chroma-Q PSU. However, I noticed that when I powered down the PSU the "twitch" got worse until I powered it back up.

More odd things. So last night, as I said, we had the same issue. I did a hard reset on the gear and it all worked fine for the show, we never saw the "twitch" again. So far today, after a reset it all seems to be working fine. I do a channel check before every show, and everything has always been working fine at channel check. After Channel Check, before the stage warmer, we have a cue for fight call, but we haven't noticed the twitch until we get into the stage warmer cue (though no one has been paying much attention to the lights during fight call).

I don't know if I will have much time to troubleshoot today as it is a double header day and the show is 3 hours long. I probably won't be able to work on it in earnest until Monday. If you have any thoughts, let me know.

[Footer]

Swap the port on the opto, I have had ports on optos get flaky after awhile. After that, sounds like a cable game. When you get the twitch, is everything wigging out at once, or is it device by device. Usually when I get "flashes" in the line, its a cable or opto issue. When you get random things in the line, its more of a termination thing.

[icewolf08]

Originally Posted by Footer

Swap the port on the opto, I have had ports on optos get flaky after awhile. After that, sounds like a cable game. When you get the twitch, is everything wigging out at once, or is it device by device. Usually when I get "flashes" in the line, its a cable or opto issue. When you get random things in the line, its more of a termination thing.

The twitch consists of: Scrollers and Icue literally twitching, the lamps in the Revs flicker, and it looked like the lenses were twitching.

As I mentioned before, it goes away after a hard reset of the Chroma-Q PSU, and doesn't return during the show. I can try a different port on the Opto. I wonder if it could be a corrupt data set in the cues, though it seems odd that it would only effect gear on one position that is addressed all over the place.

[mrb]

I have had this happen due to ground loop problems. Check your data cables and make sure you dont have one where pin 1 is connected to the shell, or the shield is touching the shell.

[icewolf08]

Originally Posted by mrb

I have had this happen due to ground loop problems. Check your data cables and make sure you dont have one where pin 1 is connected to the shell, or the shield is touching the shell.

I will look into this.

Here is an update. Second show is about to start, no fight call before this performance. Powered everything up and skipped the fight call cue, and everything seems to be working fine. So, I can't explain how a possibly corrupt cue would cause an issue like this that was isolated to one position.

[McCready00]

are you using 120ohms xlr5 cables?

[soundlight]

I've had issues with the DMX buffer card in a Chroma Q power supply screwing with a DMX signal before. When the issue started, it was similar to what you are describing. Switch out the buffer card with a new one from AC lighting. If that isn't the issue, it's always good to have a new buffer card around.

[icewolf08]

Originally Posted by McCready00

are you using 120ohms xlr5 cables?

Thanks helpie. Actually I run my DMX on barbed wire insulated by garden hose.

Originally Posted by soundlight

I've had issues with the DMX buffer card in a Chroma Q power supply screwing with a DMX signal before. When the issue started, it was similar to what you are describing. Switch out the buffer card with a new one from AC lighting. If that isn't the issue, it's always good to have a new buffer card around.

This is interesting, do you think it would make a difference if I put the CQ PSU at the end of the daisy chain? I could get a new card, but if that is the case, i may as well just replace the PSU with an Apollo SmartPower 150, they are much better units (though slightly less wattage).

[soundlight]

Originally Posted by icewolf08

This is interesting, do you think it would make a difference if I put the CQ PSU at the end of the daisy chain? I could get a new card, but if that is the case, i may as well just replace the PSU with an Apollo SmartPower 150, they are much better units (though slightly less wattage).

In our case it didn't matter where in the chain it was. It was like it was passing dirt through as well as reflecting dirt back. It got so bad that nothing on that run worked.

[icewolf08]

Originally Posted by soundlight

In our case it didn't matter where in the chain it was. It was like it was passing dirt through as well as reflecting dirt back. It got so bad that nothing on that run worked.

This is good to know as my CQ PSUs are pretty old and have seen better days. Did you experience any other symptoms? Do you happen to know what the buffer cards run? Maybe I will call my local vendor on Monday.