DMX terminator issues?

@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.

DMX can be a fickle beast. A problem anywhere on the line can manifest in various, sometimes unexpected places.

I had a whole run of fixtures on a pipe, mix of VLs and SeaChangers. The first fixture wasn't responding. Swapped cables, still no go. Everything else was fine up until the 10th fixture. When I unplugged the DMX in to that fixture, the first fixture started working. Jumped the DMX around the #10 fixture and the downstream ones started working. Not only was the #10 fixture not passing DMX, it was causing reflections on the line that messed up the first (and only the first) upstream fixture on the line.

Also had similar issues with RDM and a pipe of SpectraCyc fixtures. The first and second fixture in line would randomly flash. It didn't affect all of them, just the ones near the middle of the physical run - 100' cable to the first fixture, then many 10' jumpers. Termination installed or not, made no difference. Turning off RDM fixed the issue.

Moral of the story is that the cause may not necessarily be located where the symptoms are showing. Break the system down into parts and test each part separately.

-Todd
 
so this is dimly (ha!) reminding me of a problem some years ago where pins 2/3 were swapped in a DMX cable ... Studio 54 it was, indeed. Imagine that either one of your cables, or the internal jack wiring in one of your fixtures has such a swap. Or more diabolically, there were an even number of 2/3 flips initially, and then the swapping out created an odd number. That might provoke at least the downstream gear to misbehave. I may not have read all the above accurately, but something to think about. Especially if any of your dimmer packs have been opened up for repair?
 
I've had this problem occasionally and it has been faulty cables, now DMX is very forgiving of bad cables but when you add the terminator it loads the circuit and exposes the cable fault.
 
I didn't describe the problem very well but if the system wiring has a high impedance due to dirty connections or bad cable then the signal can still get through until you load it up with the terminator you may well find that the system works up to the high impedance point, N,B. testing with a multimeter is a d.c. test and does not tell you the working impedance,, for this you need a DMX tester. A good clean of connectors may be all you need.
 

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