Automated Fixtures VL3000 Erratic behavior

[DayOne]

Hey Guys:

First, here's my set-up:
8 - VL3000 moving head spotlights. (28ch each)
Hog3 PC to control all moving lights.

The DMX is hardlined through 5-pin from the board to the first light and then daisy-chained through the rest of the instruments. There are no dimmers in this system, just the 8 movers.

The Problem:
With all of the units connected in the fashion described above, I lose the ability to control the first unit (hangs dead and gobo wheel spins continually) and the second unit begins behaving erratically (color wheel not indexing). the other 6 units behave properly though.

My Troubleshooting:
If I unplug the DMX cable on the first instrument that leads to the other 7 instruments, I gain full control over the first instrument and it behaves properly. After this, I go back to my default configuration from above.

If I unplug the DMX cable on the second instrument that leads to the other 6 instruments leaving a chain of the first two VLs hardlined to the console, then the two lights behave properly. After this I go back to my default configuration from above.

If I bypass the second instrument completely, the first instrument does not respond to control, but the remaining 6 units behave properly. Again, I go back to default.

If I unplug the DMX cable on the third instrument that leads to the other 5 instruments, then my original problem occurs. Again, I go back to default.

If I unplug both cables from the third instrument, the first two lights behave erratically.

My Understanding
My understanding of what I have said above leads me to believe that I have a bad DMX cable between my 2nd and 3rd instruments, however in my default configuration I have full control over instruments 3 through 8. How can this be? Any help is greatly appreciated!

Notes:
- All 8 VL3000 units have been initialized with the same settings and they are addressed properly (we double checked this)
- We checked our software, the problem occurs no matter the show loaded.
- It happens with both the Hog3 and Hog2 software
- After a trip to the shop (all new belts inside, new lamps, a general spruce-up) for all 8 units about a month ago, they worked fine together for about 3 shows, then the issues started.

 

[derekleffew]

Is a terminator, DMX plugged into the last fixture in the chain?

I agree it sounds like a bad cable, but can't figure out which cable it is. I've had similar symptoms, where one bad cable would cause a problem a couple of fixtures away, either up or down the line. Since it was a rental, we just replaced ALL the cables, throwing the suspect ones back in the box for the shop to figure out. One cold solder joint on one pin of one cable can really ruin your whole day.
A continuity cable checker may not reveal the problem, but a DMXter or DMX signal tester likely will.

Another thing to try: Go from the console into light #2 first, then daisy-chain through all the others. With a long cable, take the output of light#8 back to the input of light #1.
Something else I've done: Go into light#2 first, then the rest. Take the spare home run (you DO have a spare home run, right?) from the opto into fixture#1 only.

One more thing: Check for good grounds in your L6-20 break-out and the fixtures' plugs. I've had that bite me before also.

...Hog3 PC to control all moving lights. ...

I believe I've read recently on some forum about data issues when using a Hog widget with long runs or lots of fixtures. Adding an opto-splitter solved that problem.

 

[TimMiller]

The problem I am betting is a bad dmx cable between the 2nd and 3rd unit BUT if you leave a dmx cable unplugged and not terminated what will happen is the signal will start bouncing back down the cable causing the fixtures to freak out. You must terminate the end of any dmx line. What I would do is when you bypass the 3rd fixture plug the cables into each other and see what happens down the rest of the chain. I have seen control problems in lights before that cause what you are experiencing along with the typical bad cables. Also never assume its just one cable you may have more. Also make sure the ground on the power cables and the fixtures are properly connected.
All electronics use that ground as the 0v reference. Without it will start to freak out. Also keep in mind just as the audio guys can get ground loops (60 cycle buzz) we can get ground loops down the dmx line. Unfortunately we cannot hear it to try and rectify it but we can see the effects from it. Here is an article by TI on ground loops on digital networks. Remember all dmx is, is and RS-485 serial protocol and the lights and controller are a series of computers. Also are you using a terminator at the end of your dmx line? I not you can make one using a 1/4 watt 120 ohm resistor wired across pins 2 and 3 on a male dmx connector.

 

[derekleffew]

...If not you can make one using a 1/4 watt 120 ohm resistor ...

Tim, you might want to rethink that value. See the footnote in the wiki entry terminator, DMX.

 

[TimMiller]

Tim, you might want to rethink that value. See the footnote in the wiki entry terminator, DMX.

Oops, high end says 1/4 watt min I normally use 1/2 watt. I should have stated that. Interesting how DFD recommends 2 watt I have never seen or heard of that. I have had terminators cause issues before. Lights all start going crazy until I unplug the terminator. Has any one else ever seen that before?

 

[DavidNorth]

Lights all start going crazy until I unplug the terminator. Has any one else ever seen that before?

Yes, I have. I see where people occasionally post that things get worse when they use a terminator. If so, then there is a cabling problem, a data cable length [or cable type] problem, or at least one bad device on line. Terminators can only either solve problems or expose them, not create them.

With non-compliant cables or very long cables, the DMX signal could be degraded enough in amplitude that the addition of another load on the line, in this case a terminator, can drop the amplitude down to where DMX is not fully recognozed by some devices causing undesired behavior.

A device with a compromised DMX receiver can cause it or other devices in line to freak out.

Here's another possibility that tricks up people.....

Most DMX devices work just fine if you only have Data+ and Common. If that is the case, and one of your DMX cables has Data- missing, then a terminator will cause misoperation or no control of fixtures after the Data- break.

With a missing Data-, and a terminator on the end of the line, the Data+ signal travels down the line to the terminator and then back up the Data- conductor all the way up to the break in the line. All of those devices which now have Data+ on both Data conductors will misbehave.

Thanks for listening.

David

 

[DayOne]

Wow!
Thanks for the great responses! Here's the thing though. These fixtures have been hung for 10 years without any operating problems beyond regular maintenance. I am going to bring the DMX terminator in to work this evening to try it and I will let everyone know what happens.

Also, I thought that the VL3000 units (along with many larger fixtures) were self-terminating if they didn't sense a cable on their output?

I also believe that I forgot to mention two scenarios that I tested that did not work.

My Solutions (Cont):
If I bypass the second unit completely so my DMX chain is 1, 3-8; then the first unit no longer responds but I have control over 3-8.

If I bypass the third unit completely so my DMX chain is 1,2, 4-8; the first two units respond erratically and the rest of the chain is fine.

Cheers!

 

[RonaldBeal]

I always start troubleshooting those problems from the far end... unplug 8 (at fixture 7)... do the first fixtures start playing correctly? if not, then unplug 7 (at 6)...etc, etc...

 

[derekleffew]

...These fixtures have been hung for 10 years without any operating problems beyond regular maintenance. ...

So nothing has changed in 10 years? How very peculiar. Still, cables do sometimes go bad over time. I'd still try replacing cables, in some logical order. Ron's method sounds like one of the easiest.

...Also, I thought that the VL3000 units (along with many larger fixtures) were self-terminating if they didn't sense a cable on their output?...

This is one of the biggest myths/fallacies in the industry. See this post. The only units I know of that are truly auto- or self-terminating are the ETC Revolution and SmartPack, both of which use the Neutrik NC5FAV-SW female XLR5.

 

[jglodeklights]

Idea of running a home run back to the control is what I would first do, if you haven't already. If that doesn't reveal issues....

I would say DMX receiver issues.

Sounds very similar to what was the case with two Apollo scrollers I had rented. Even with home runs to different outputs on the power supply, and even changing the power supply, they were "shuddering." They were fairly low on hours of usage, and a total of three ended up being pulled from use during the week. Sometimes things happen to moving stuff.

And I see you are in Philadelphia, like me. Our power here is somewhat ridiculous, and you can go ten years without having an issue, only to one day come in and find two dead PC towers in your office. Anything electronic is susceptible to issues coming off the powerline. I've worked servicing PCs in the past, and have found surges as likely culprits to do anything from completely frying the MoBo, HDD and Power Supply to only killing the USB controller.

 

[photoatdv]

"If I unplug the DMX cable on the second instrument that leads to the other 6 instruments leaving a chain of the first two VLs hardlined to the console, then the two lights behave properly. After this I go back to my default configuration from above.

If I unplug both cables from the third instrument, the first two lights behave erratically."

I'm confused here. If you unplug the cable leading from #2 to #3, whether or not the cable between #3 and #4 is plugged in or not should have zero effect. Am I reading this right in that unplugging the cable between 3 and 4 affected the first 2 when they had no connection to 1 or 2?

 

[DayOne]

Hey Photoatdv, it's a matter of whether you are disconnecting a faulty cable or leaving it connected. However, I have exciting(ish) and yet confusing news! I tried two more things tonight when I had the time and had some great responses.

The Update:
First, using my default configuration (from the OP), I plugged a terminator into unit 8. When I did this, the first two units stopped behaving erratically and homed. HOWEVER, I lost control of all units except for number 6. I pulled the terminator from unit 8 and went back to my default configuration.

My next test was to run a new DMX cable between units 2 and 3 (the obvious[?] choice). When I only had units one and two connected to the Hog3, I had full control over them both. However, when I plugged in a working DMX cable to the output of unit 2, it went dead and only unit 1 responded, even though the other end of the cable wasn't attached to anything (and it was terminated). Strange right? After this, it was back to the default config (DefCon).

My next test was to run a new DMX cable between units 1 and 2 and leave everything else the same; meaning that I should have had control over all 8 units. However my original problem persisted. It was back to DefCon.

My final test for the evening (since my battery operated lift was dying) was to run a homerun from unit 1 to unit 3, ignoring unit 2 and any cables attached to it. Essentially leaving me with 1------> 3 ---> 4 --->7 through 8. When I did this, I gained control over all 7 units and they behaved properly.

My Understanding:
As I see it, the problem seems to exist in combination of three places as shown below:

1 ---> 2 ---> 3 through 7.

It is some combination of a cabling problem with the cables between 1 and 2 along with 2 and 3; or an instrument problem with unit 2.

My next test (that unfortunately cannot take place until the new year) is to replace these two cables and confirm this is the problem and not the instrument itself. However, there is a nagging voice in the back of my head that wonders about that first test I did with the DMX terminator and the strange behavior that occured. I can't wait to hear what you guys think!

 

[derekleffew]

I know we've been focusing on a cable issue, but the next thing I'd try is to swap units 2 and 8, and re-address.

 

[DayOne]

I know we've been focusing on a cable issue, but the next thing I'd try is to swap unit's 2 and 8, and re-address.

Yeah, I did re-address the unit 8 to the same address as 1 and unit 8 did not have any problems. Also, I cannot physically swap the units because the are hung from the ceiling of a very elegant ballroom and it requires two men on a scissors lift to do that.

 

[derekleffew]

Yeah, I did re-address the unit 8 to the same address as 1 and unit 8 did not have any problems. Also, I cannot physically swap the units because the are hung from the ceiling of a very elegant ballroom and it requires two men on a scissors lift to do that.

Okay. How about ---->1-->3-->4...-->8---long cable--->2 ?

 

[DayOne]

Yeah, I think we may try that eventually if replacing the two DMX cables I talked about the other night does not work. However, like I said we are in a holding pattern until after Christmas. Thank you everyone for your help!