DMX terminator issues?

ACTSTech

Well-Known Member
Well, due to the total shutdown I won’t get to play with my issues, so I’ll ask my question here.

Just started (and ended!) a run and had weird DMX issues. We were running ETC Nomad off a laptop through the 2 universe dongle. Universe 1 was front of house, universe 2 was on stage. Universe 2 went through a DMX splitter due to length of run. At the end of every line, I put a DMX terminator in the final instrument. In every case, this caused weird flashing, strobing, and non-responsive instruments. The last thing on the front of house was a dimmer pack for ellipsoidals, and the pack wasn’t overloaded (only 3 S4 575w instruments and they were never all on at once, plenty of clean power running to them.). When I’d try to run the show, the entire FOH would flash or not respond to the DMX, or would temporarily work then shut down. After replacing every dimmer pack, hoping it was a faulty pack, I forgot to plug the terminator in the last pack and the lo and behold, the system responded perfectly. When I went back up the ladder to plug in the terminator, the system went haywire again.

On stage, same story. The final four instruments in the chain were LED pars, and when I plugged in the terminator on the final instrument, the last three stopped responding, flashed, gave garbage output. When I pulled the terminator, everything ran. On stage, run 1, 2, and 3 all had terminators and didn’t give me a problem, but run 4 did.

Did I do something bad or was this my gremlin on this show? Does anyone have any experience with this? Like I said, I didn’t have time to tinker because of the circumstances but it’s my puzzle to think about.
 
Fascinating.
I had a job in a HS last year it had S4 PARs with Source4WRD engines. Every time we terminated the lights went disco freak out. When we removed the terminators things returned to mostly normal but a couple of fixtures quit responding all together. We traced this particular problem to a programming error in a touch panel, these were lights in an Acoustic ceiling.
 
Every time we terminated the lights went disco freak out. When we removed the terminators things returned to mostly normal but a couple of fixtures quit responding all together.

Exactly my issue. I tested the lights prior to running the program, just to make sure there was power, the instruments were functional, lamps were good, etc... Once the DMX was terminated, disco. Pull the terminator, good. I checked my patching to make sure it wasn’t bad addressing, and it all looked good, but the problem seemed to be the terminators. And just at the end run on each universe, which is curious. I’d love to get in and tinker, but that ain’t happening for a while, and once life reopens we have to tear down so I won’t get the chance. I’ve combed the ETC forums and here, I just didn’t know if I was the only one who had the issue.
 
The most common reason for a DMX line to fail after being terminated is that one of the + or - wires is disconnected. DMX is a differential signal on two wires and if one becomes disconnected then the receiving device might still work. Applying a terminator essentially eliminates that possibility.

I'm not sure that this is happening in this case as it seems to be on multiple lines. I would suspect the splitter. In any case, a terminator will test the integrity of the line.
 
 
I'm not sure that this is happening in this case as it seems to be on multiple lines. I would suspect the splitter. In any case, a terminator will test the integrity of the line.

I would have suspected the splitter except my FOH run wasn’t on a splitter, straight run from a brand new dongle over brand new DMX cable.

And @derekleffew I did read that forum, but thank you for reposting so it’s easier to reference. I understand the basics of a broken system, but when the FOH disco started, I thought it might be a bad fuse in the dimmer pack, but they were fine, so I started swapping out packs. If there was a break in the system, wouldn’t that have been solved if I took out the bad dimmer pack? All the patch cable in the FOH run was new, but I did test it and none of them registered bad. That’s why I’m stumped. It discoed before the computer was even powered on, just packs connected by cable.
 
Did you check your terminators? Are they 1/4 watt 120 ohm resistors on pins 2 & 3?
The other thought is RDM gremlin, but I don't know why it would only be a problem when terminated.
Good luck,
John
 
It discoed before the computer was even powered on, just packs connected by cable.

Hmm, does sound like a stumper. Your last comment is interesting. Some questions.

I assume the DMX splitter is also an isolator? Does it work with RDM? Are the terminators all the same? Made by major manufacturer? Did you ever run the system with just the splitter and not FOH connected? Did you use an external monitor? Gadget II interface?

Other than my last post, there are some other causes of disco lights I have considered. One pertains to ETC. Is somehow RDM discovery getting enabled and the terminator is affecting that? I'm not sure if that could happen with the computer off.

Something else I consider when the problem might come and go is ground loops. Opto-splitters are supposed to prevent ground loops but then you had one run without it. The terminator would have to be connecting the signal common to the case, which is unusual.

Since it is ETC you could call tech support and see if they have any thoughts. If the show has ended you may never know. Someone I continue to miss here is David North.
 
FAR from a DMX expert (or even RKI) here, but could there be multiple terminations somewhere? Maybe an instrument with internal termination switched on when it shouldn't be? Improper terminations often mess things up.
This could explain the LED pars, the dimmer packs don't make sense though.
@ACTSTech what makes and models are the pieces involved?
 
I was also think plugging in a terminator on a self terminating device could give some problems.

Also curious of the dimmer and other fixtures involved in this scenario.
 
I was also think plugging in a terminator on a self terminating device could give some problems.
A terminator would not cause any problems at all with any of the known self-terminating devices.

I've read the S4LED manual from front to back and find no indication these fixtures "self-terminate" the DMX. Maybe I missed it. Can you cite your source on this? In a wider sense, I am curious if there are actually any fixtures being made that "self-terminate". Seems like a myth as wouldn't they have to have some kind of switching XLR jack on the DMX out/thru to accomplish this without human intervention?
and the subsequent post.
 
Could it be one of the cables has the shell connected to the signal ground (i.e. like some microphone cables do)? This could cause a hum loop. But it's unusual that putting the terminator on would cause flashing. Another maybe is a device thinking it has no DMX gettign to it (termiantor is taking a marginal signal out, perhaps, or one leg is broken) and is going into standalone mode, outputting the patterns it's runing on its DMX out. Some dj style LED pars have a standalone flah mode in the abscence of any DMX input.

Just a couple of wild guesses. The usual advice would be to unplug everything and connect known good cables and terminators to one device at a time, prove it out, then add one fixture into the chain at a time, but clearly that stage has left.
 
@avkid and @Amiers (plus everyone else), the FOH run was Leviton D4DMX-MD5 portable dimmer packs, each one addressed correctly, mix of S4 ellipsoidals lamped at 575w and Altman 3.5Q ellipsoidals lamped at 500w. Each dimmer was individually plugged in to a separate 20a circuit, clean, fairly stable source. DMX run was average. 100 foot cable from Gadget II dongle to, pack 1, 10’ DMX (not microphone) cable from pack to pack. As I hung the run, I started doing it the hard way, as I’m not smart or efficient. I ran my power and DMX up to the batten and climbed up the ladder, gaff taped, climbed down, moved the ladder, up, down, repeat. When pack 1 was up, powered, instruments plugged in, it dawned on me that I should have checked if it worked, so I powered it on, just used the menu button to turn on each channel, all the ellipsoidals worked, good to go. Repeated the process until the whole FOH was done. Everything tested fine. Got off the ladder took a break, rested my legs.

Time to do a rough focus. Went to the breaker, turned on power to the dimmers, disco. Swore a little. Went to each pack, made sure no addresses were overlapping or that I accidentally turned on a program or something. No change. Checked connections. Changed 10’ DMX cables, all new, all test fine, no change. Powered down. Changed 100’ run! Swore a lot. No change. Turned on pack 1 only, fine. Turned on pack 2 only, fine. Turned on pack 3 only, fine. Turned on all 3, disco. Turned on different combinations, disco until I just did everything but the third pack. Then it was stable, so I had two more Leviton packs. Swapped out 3 (and plugged in the terminator). Powered up, disco. Swapped out 2, disco. Ran out of Leviton packs, switched to emergency old Optima packs, swapped out 1, had to plug in a 5 to 3 pin adapter. Still disco. Still when I turned on the last pack. Swapped out 3 again, forgot to terminate and it all looked fine. Fired up the computer, everything worked. Looked at the pack, terminator is still in the pack. Swear as I go to the kit, grab a 3 pin terminator, climb the ladder for what I promise myself will be the last time ever, plug in the different terminator, disco. Unplug the terminator, fine. Plug in to make sure I wasn’t seeing thing, disco. Unplug, fine. Ask someone to play on the computer, run some cues I programmed for testing, responds. Plug in the terminator, Studio 54.

I honestly don’t remember what splitter we had on stage, but as I hung the lights, I daisy chained them and at the end of each run, I terminated the last light. There were 4 runs from the splitter, the end of each run was terminated with an identical terminator. 1st electric was good. 2nd electric was good. 3rd electric was good. 4th electric had some weird runs due flats, so the cabling was longer between instruments, so I was a little concerned. Last 4 instruments were cheap LEDs, don’t honestly remember the brand. Test 4th electric, last 3 instruments turn on and either stay at cue 1 and don’t respond or disco. I kind of learned from my mistakes, so I pull the terminator, they come back in line. Run test cues, good.

I would agree 100% that a broken circuit would cause issues. I would agree 100% that I’m often a moron. But 6 different packs, new DMX cable, different terminators, something’s not right. And in the past, when I didn’t terminate these same packs, we’d occasionally get some DMX chatter that made us get a flash or wonky responses, but it was a different light board and system, this was the first with the Nomad. I’m not blaming ETC at all, I’m just trying to get my head wrapped around the puzzle. We used two universes just because of cables. The last addressed and used instruments on each universe (LED light on one universe, dimmer pack on a second universe) gave me fits if I terminated them. 1st, 2nd and 3rd electrics on stage, a mix of LED and dimmer packs all ended their lines with the LEDs and all got terminated, none of them ever gave me a problem. And now with the covid thing, I have all the time in the world to play and can’t go play. And once we get off the restrictions, we have to tear down.

Perhaps I just have too much time on my hands.
 
Are all your DMX cables correctly wired? No pin 2/pin 3 swaps? DMX "disco" happens because of data reflection or data corruption (timing or s/n).

@jfleenor , the Bat-signal is flashing!
 
I am suspicious of the new cables. Just because they are new, doesn't mean they are built correctly. I recently grabbed a 10' mic cable that came with a top brand microphone. I plugged it into the mixer, and it hummed. Then, I grabbed another cable, plugged it into the same channel, and it was clean. Investigation revealed that the shield was sloppily crimped into the strain relief, which bonded the shield to the connector shell. That's a no-no.

A lot of cables are made very poorly, with bad quality connectors now. It's all part of the race to the bottom in prices. In this case, I wouldn't be surprised if they wired them wrong in some way that a continuity check won't reveal, such as the shield and signal wire swapped to the wrong pins.
 
@FMEng I thought the same about the cables, because I’ve had mic cable from top notch companies come bad. I’m just confused as to why it was happening at the end of the universes. If I used the same cables in the on-stage runs, wouldn’t you think the 1st, 2nd and 3rd electrics would have issues as they all had terminators? Neither universe was full, the LEDs ate up addresses, but I wasn’t over 300 in either universe. I did switch out one LED because it wasn’t responding even after the DMX issues, but in my tinkering here at home (shhh, I do plan on returning it) the dip switches on 7 and 8 are faulty, so I’ll replace that myself. It’s the end of the line that confuses me.

If I had access, I’d go repatch everything onto one universe, run miles of cable and daisy chain the entire thing, just to see if the last instrument still went wonky. I’d probably use my ancient multimeter to check the cables too, but the el cheapo handheld tester said they were good. Oh well.
 

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