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Wacky DMX issues

Discussion in 'Lighting and Electrics' started by icewolf08, Sep 8, 2008.

  1. icewolf08

    icewolf08 CBMod CB Mods

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    Here is a new one for me. I was testing gear before focus today (want to make sure everything turns on for the LD) and discovered a very odd data issue. On my 1st electric and 1A electric all my DMX gear was wiggin' out, the scrollers wouldn't stay put, mirrors just kept roaming around, and the MLs just plain old didn't do anything.

    So, my first inclination was a bad cable. I started by pulling the run from the scrollers on to the rest of the chain (scrollers are first off the opto). Lo-and-behold they start working fine. So I start hopping from device to device, plugging them in one at a time, and everything works until I get to the last ML, plug it in and everything goes nuts again. So, I figure maybe it is a bad terminator, yet when I pull out the terminator everything starts acting normal. I popped in a new terminator and I was back to everything wiggin' out. Seems odd to me that the little device that is supposed to solve all the problems is causing them. Now, with this unterminated line everything works just like it should. Go figure!
     
  2. STEVETERRY

    STEVETERRY Well-Known Member

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    Sounds like a marginal driver in the opto that cannot source the full EIA-485 load, including the terminator.

    ST
     
  3. JD

    JD Well-Known Member

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    Could also be that the light has a built in terminator that is switched on. You would then have two terminators on the line which would half the signal strength.
     
  4. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    Have you tried the mover alone with and without a terminator to isolate that it is the problem? What about a short in the mover just before the data leaves? What happens if you put a scroller after the mover in the chain?
     
  5. beltsvillecrucib

    beltsvillecrucib Member

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    Is the ML in question a house fixture or a fixture you brought in? I'm no SteveTerry or JD, but is it possible that the fixture could have a bad DMX out and you're getting reflections back down the line? This is much more likely to happen with a rental house fixture that has seen the back of a truck a hundred times this year, but still could happen to a house fixture.

    Maybe try putting a fixture after the ML in question in the chain and see if it still bugs out.

    I could be way off though...ST?
     
  6. len

    len Well-Known Member

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    All good advice. I would run a test line direct from desk to the wacky ML. No terminator. Then add the terminator. Then test output after the fixture. the more complex a system, the more things that can go wrong. Best solution is always to try and strip down the system to the fewest possible parts and add them back in one at a time. Time consuming but really the surest way of isolating problems.
     
  7. icewolf08

    icewolf08 CBMod CB Mods

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    I did try putting the terminator after the scroller PSU and still got the wackiness, so I would tend to agree with ST. This is an old DFD opto that has all 3-pin outputs, lives on the grid and runs almost 24/7/365. It feeds data to any flying gear we need. This is the first time that it has acted up though, but it wouldn't surprise me. The other outputs from it seem to be working fine though. Right now things are working, if I run into any further issues I will post them. Also, the fixture is a house fixture that is only a little over 1.5 years old and has been working great.
     
  8. TimMiller

    TimMiller Well-Known Member

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    I have run into this problem before. It is commonly a result of using mic cable instead of DMX cable, esp since your system is 3 pin. I would try just plugging in a mover instead of a scroller then the terminator to see if you have the same problem. There could be signal degeneration further upstream, and you are seeing the results further down the line. Personally i would just go on without using a terminator. Also some gear does auto terminate, so using a terminator will cause problems. Also you can try using a different output out of the splitter. Each output is independently driven so the problem should follow along with that output in the splitter if it is the splitter. New opto chips are easy to replace, and readily available at many electronics stores such as digikey.
     
  9. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Please validate this statement by citing from any manufacturer's documentation, as we just had this debate in another thread, and I would appreciate being proven wrong.

    Alex, you DO have one (or several) of these: Fleenor DMXTSTR, don't you?
    (Disclaimer: Not the solution to diagnosing EVERY DMX issue, but immensely helpful with MOST of them.)
    [​IMG]
     
    Last edited: Sep 9, 2008
  10. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    Hey Alex did you try bypassing the opto and running a line straight to the console to isolate if the problem is in the opto or the gear?
     
  11. indyLD

    indyLD Member

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    Alex, much good advice has been given and weird DMX faults can be tricky to trace, so I don't want to clutter up the thread.

    I would not totally discount a cable issue. Putting a terminator on a "one legged" DMX signal will make a seemingly "working" system break (of course, the system is actually already broken). Also, using an opto can also hide underlying cable issues - I would try bypassing all DA's and get signal straight from desk to fixtures with no termination. Then you can begin fault finding cables on a level playing field either in sequences or by splitting the rig in half (more details in the OSL DMX Fault Finding Guide)
     
  12. icewolf08

    icewolf08 CBMod CB Mods

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    I do have a DMXter, what I wish I has was the $1.2K for a DFD Gizmo that couls tell me more than just pulsing LEDs and of course can continuity test and all. On this note, is it worth spending $300 on the similar Elation DMX Dr. II or should I just see if I can fudge that money from my budget for a Gizmo? Or are there other DMX analysis tools that are good that run less expensive?

    Bypassing the opto would be a project. Getting a run from the console to the batten is over 400'. Will look into it though. I have been trying to round up the funds to update data runs around the theatre, and we will probably re-do all data distro after our 2010 season when hopefully we will be putting in new consoles.
     
  13. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    I think you've confused DMXTSTR, and DMXter, to which the Elation unit cannot compare. Here's a handy, biased chart comparing features of various units, from Interactive Technologies. The Lil'DMXter was the first, and probably still the best, but for that much money I insist on a numeric keypad.
     
  14. len

    len Well-Known Member

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  15. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    Well you could run 400' of cable, but my favorite way to bypass the opto would be to stand at the opto, unplug the line in, unplug the line out, and then connect those two lines together. :mrgreen:

    I know, you're having a bad day. That's why we are here.
     
  16. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Alex has previously stated "This is an old DFD opto that has all 3-pin outputs" so if the input is 5-pin (most likely), then it's not as easy as you make it seem, now is it? Getting three males inserted into five females is problematic, as someone always feels cheated or excluded.:oops:
     
  17. len

    len Well-Known Member

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    And thus is the spit take of the day!
     
  18. Sony

    Sony Active Member

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    Somebody has got to have a 5 to 3 pin DMX adapter somewhere... If not you can make one in about 5 minutes.
     
  19. icewolf08

    icewolf08 CBMod CB Mods

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    Bad day? It has been a rough week. We lost a day of focus due to a wonky scheduling snafu... Something about a football game later in the run that required us moving a performance to earlier in the run... Yeah, I don't really understand it either. So I never really got the time I usually have to ring out the system. I feel like I have been working my crew to death (not to mention myself, though I seem to be doing OK) and I really don't want to burn them out on the first show of the season or make them not want to come back.

    The good news is that everything seems to be working. We are in dry tech tonight, and then our first 10/12 is tomorrow and we are away and teching. Focus notes and touch ups to come, plus finishing all the practicals that I didn't even see until yesterday.

    I love live theatre!
     
  20. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    How do I report this post to the senior team? :twisted:
     

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