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Control/Dimming LED Decoders stops working until turned off and on again. We're all stumped.

Discussion in 'Lighting and Electrics' started by Stages Electrics, Jun 14, 2019 at 5:23 PM.

  1. Stages Electrics

    Stages Electrics Member

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    Hi everyone,

    We are using some LTech DMX512 24 Channel decoders ( in one of our shows and we're having a strange problem with them. Every so often (but way too often) we need to turn them off and on again. We've had this issue when they turn on for the first time in a show and halfway through the show and we can't figure out what is going on with them. Our lightboxes are made up of SMD5050 LED modules, each channel using fewer watts than the output of the decoder.

    We've narrowed it down to the decoders and specifically a power issue on the decoders.

    Things we've found interesting but still puzzling
    • DMX is still going from decoder to decoder.
    • We've swapped decoders out for brand new decoders of the same type and experienced the same issues.
    • These decoders have been used in previous shows in a similar application and have never had this issue before. Plenty of other issues, but never THIS issue.
    • Each decoder is only running 12 of the possible 24 channels except for one. Problems persist with both.
    • We had no issues like this until we experienced a brownout in one leg before everything was connected to line conditioners. We changed bad decoders and bad power supplies out. Since then we've continued to change out decoders before we realized that they needed to cycle power.
    • This show is kind of hard on them. They turn on and off, change color rapidly, and cycle through rainbow colors.

    Issues we've eliminated
    • DMX, see above reasons
    • Overheating
    • Power surges and brownouts (line conditioners)
    • Bad LEDs (they're still kicking someway somehow)
    If anyone has any idea what is going wrong, need more information, have questions or possible fixes I'd love to hear them. Thank you!
    RonHebbard likes this.
  2. RonHebbard

    RonHebbard Well-Known Member Premium Member

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    Burlington, Ontario, Canada
    @Stages Electrics What happens if you power your devices from utility duplex receptacles, specifically NOT from power from dimmers or solid state non-dims. Non-dims switched via mechanical (often referred to as "air gap") relays could also be utilized. Dimmers, regardless of what level they're parked at and / or non-dims switched via solid state devices (dual SCR's, TRIAC's, etcetera) require an amount of turn on time clipping a minute amount from the rise of each half of the positive and negative sine waves. This clipping of the waves' rise often plays havoc with many power supplies receiving their primary power from such sources.
    @Ron Foley Would you care to comment?
    Ron Hebbard
    FMEng likes this.
  3. JD

    JD Well-Known Member

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    North Wales PA
    Line filters are not going to replace the missing waveform. As Ron said, power them off a regular old wall outlet, or an "air gap" non-dim module. Another issue is that the idle current may be too low. When using electronic equipment on any dimmer, even parked, you open up a can of worms. Throwing a 100 watt incandescent lamp on the circuit as a ghost load may make them behave better, but your best solution is to go with real utility power that doesn't have a dimmer in series with it.
    RonHebbard likes this.
  4. Amiers

    Amiers Renting to Corporate One Fixture at a Time.

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    Lighting Floor Tech
    Phoenix, Az
    I also vote the decoders on the dimmer are messing with the rest of them.

    Easy test take the dimmer decoders out of the dmx run and see if they still act up.
    RonHebbard likes this.
  5. EdSavoie

    EdSavoie Well-Known Member

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    College Student
    Ottawa, ON, Canada
    As a side note, DMX should pass through unit to unit regardless of if they are powered on as you've noticed, the DMX in is wired directly to the DMX out, as devices "tap" the bus
    RonHebbard likes this.

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