Twitchy scrollers

[ackdp]

I have been having problems with Wybron Forerunners, specifically they have a habit of twitching randomly when in use. Some may simply twitch forward and then back, some twitch only forward some only back. I know that we had to change out the chips recently to deal with a data issue, and they now all have a 26 chip. Because they are highly used and needed for shows we are having them looked at by a professional, however just for my own curiosity has anyone else had this problem and is there anything I, as a amateur fiddler and tweaker at best, could do to fix them?
As secondary notes they do this little dance in multiple spaces, with different power supplies, with DMX terminators.

 

[JWilsonLX]

How are you running them? Is the data in a cue, are you running them from a sub, or something else? I've had that issue with Apollo Smart Colors sometimes when running them from a sub, depending on the control board.

 

[skienblack]

I have also seen a problem when there is not enough power available on the 4 pin DMX circuit. I have even seen only one of the scrollers in the daisy chain twitch when the others work fine. All of this was solved by splitting it into two circuits from power supply.

 

[jglodeklights]

I've had this problem with Apollo SmartColors. One of the rented scrollers was twitching. At first it appeared to be a termination problem as the one next (also last) in line was twitching also. Ok, terminate back to PSU. Hmmm, nope. Home run to PSU and remove everything else. Hhmmm, still twitching. Remove it from the line. "Hey, the last in line is working fine now!" Oh, crap, Unit 1 on Box Boom is not moving. It's not receiving data. Crap.

This is what happens when a DMX device fails to receive data properly, either due to damaged connectors (common as people like to yank things) or due to hardware issues inside. A failed DMX controlled power supply can replicate this and make conventionals flickker! How annoying.

 

[Van]

This really reminds me of a problem I had once. Did all the checking and it came down to one bad cable. A loose solder was causing a reflection and making everything dance when it was supposed to be silent/.

 

[ackdp]

How are you running them? Is the data in a cue, are you running them from a sub, or something else? I've had that issue with Apollo Smart Colors sometimes when running them from a sub, depending on the control board.

It happens in both. however at this point I am having trouble getting past loading a new scroll without the reel running away.

 

[techno89]

I would try to get a cable test and even though it would be tedious I would test all the cable for issues.

 

[Benjod82]

We have had similar issues with our Forerunners, and have had the chips changed and still had similar issues. After much guessing, checking and elimination with our local vendor our best estimate is that we were getting a weak DMX signal and were able to "solve" it by actually unterminating the last repeater in our system. That being said, we never had any problems with any other DMX devices daisy chained off of the scoller power supply (whether terminated or unterminated).

I won't miss the scrollers once we can get entirely to LED.

**Disclaimer** Our low voltage system installed 10 years ago has never completely or properly worked.

I would try to get a cable test and even though it would be tedious I would test all the cable for issues.

 

[Lotos]

Had the same issue in the past with Chroma-Q's... Multiple times...
It always seems to come down to a bad cable, for me at least... They test okay on a cable tester, but if you can swap cables one by one (sucks, I know...) you'll eventually find the culprit.