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Dimmer Buzzing...No Output

Discussion in 'Lighting and Electrics' started by cw4u, Jun 4, 2009.

  1. cw4u

    cw4u Member

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    I've got a Chauvet DMX-4 dimmer that is making a buzzing sound on circuits 1,2,4. Circuit 3 works perfectly fine. If I plug something into 3 the sound doesn't occur. But, if I plug something into the others, it does.

    I know these things are cheap, but is their anything I can do to fix the problem?

    Thanks.
     
  2. church

    church Active Member

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    it depends on your knowledge of electronics. The part that usually fails on these and other dimmers is the TRIAC.

    If the faulty channels are staying on permamently then it is likely the TRIAC has failed - an easy repair if you have TRIACs or know someone who does. If the channel is dead have you checked the fuse - it is quite common for the TRIAC failure to occur with a fuse failure. This often happens when someone shorts a channel out - loose wire in a fixture incorrectly wired cable. The TRIAC fails as a short circuit which then results in the fuse melting. TRIACs fail faster than fuses. Again the repair is easy. I just repaired a unit two weeks ago that was exactly what you described. The owner had plugged in a home made cable which had a reversed ground and live wires. No problem until they plugged it into a fixture. It took three channels to die before they realised.

    The TRIACs are BTA16 a cheap device under $5 each but if you don't have them you need to buy the minimum order and pay shipping which is a different story.
     
  3. DAE

    DAE Member

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    I checked mouser.com where a BTA16 is $2.74 and a BTA24 is $4.67. I would recommend fitting a triac that is four times the rated current of the dimmer channel, however the BTA41 is a larger TOP3 package and is $10.90. The BTA24 is a 24 amp triac in the same TO220 package size, that will make your dimmer more robust. You need to check the data sheet to see if the triac in your dimmer has an insulated metal tab. Then hopefully you only have to change a fuse next time.
    Speaking of fuses, ceramic fuses cost more but rupture quicker so have a better chance of protecting triacs. A glass fuse has a slower rupture time.
     
  4. JD

    JD Well-Known Member

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    BTA24 is a direct drop in. (Mouser 511-BTA24-600BW) I've swapped them out every time I work on such a pack. At 25 amps, at least you have some headroom. These packs are rated at 10 amps per circuit, 2400 watts total. I like to think of them more as 600 X 4 packs.

    Now, your complaint about the buzz is a bit puzzling if the device is open. Buzz usually comes from the choke. Some high temp GE silicon fixes that. As to why you would get any noise if the Triac is open doesn't click.

    EDIT:
    Ahhh... Now is a good time to remind everyone that unless you are qualified to do such work, we recommend you take the unit to a qualified service center.
     
    Last edited: Jun 4, 2009
  5. David Ashton

    David Ashton Active Member

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    A buzzing sound is caused by a choke vibrating, I never heard a noisy triac, you may be able to quieten it down by painting it with epoxy resin or just change the choks.
     
  6. church

    church Active Member

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    The response time for a ceramic fuse that fits into a 3/4 inch fuse holder will not save a TRIAC in the event of a short circuit to ground or neutral. Typical fast acting glass or ceramic fuses are 500ms, unfortunately without surge current protection the TRIAc will fail under short circuit conditions in the first 4ms as the waveform moves through the first positive or negative going quadrant. The current transient di/dt will exceed the device maximum value and its all over for for the TRIAC.

    With my original post I was going to provide information on how to to check out a TRIAC but thought better of it. Thinking that if you don't know how to do this you should not be removing the cover from the unit and your diagnostics are limited to checking the fuses and finding someone who can repair it.

    However that said discussions on these issues are of value for people who do have knowledge in electronics etc. Also we all had to learn and we are at risk of not sharing any information about anything in case someone uses the information and does something stupid with it. If we keep going this way before long access to books and other sources of information will be highly controlled and available only to a privellaged few.

    You can easily find information on how to test devices on the internet and through electronic component manufacturers websites if you have the interest and ability to read. However without a certain level of knowledge you will not be able to search for anything. The various posts on this thread have provided information that anyone who is interested can use to search the internet and find out more.
     
  7. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    So CW4U, take it to an electrician. The good news is you have a very portable dimmer you can take in instead of ordering a field service call. You also should be able to take it to any electrician in town, you don't need a theater repair shop. Call around and say you've got a portable dimmer with what appears to be three bad TRIACS and ask how much it would cost to repair them.

    Secondly, I want to throw in my opinion of this thread in general as a senior team member...

    I feel you guys have done a good job walking the line on this one. You've given good information that someone with electrical knowledge can use to do the repair them self. At the same time, you haven't given out really detailed how to information that could get a 12 year old killed. That's the line we try to draw here. The danger is always that some young person out there is going to read what you post and try to do it him self without proper training and get killed because he didn't unplug it first or some other dumb mistake. Yes it is "gate keeping" of information, but the last thing we want is for CB to be responsible for a death or horrible injury. There is a place to learn how to safely do electrical work... it's called College... not the internet.

    That said, if someone is asking this question, they probably don't have the knowledge to safely fix it. If you have to ask the question, you don't belong fixing it, take it to a certified electrician.
     
    Last edited: Jun 5, 2009
  8. jonliles

    jonliles Well-Known Member Fight Leukemia

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    And if you can not get an inexpensive repair ($/hour will kill you), go to ebay and buy a $70 pack (Optima's?) or even better would be to contact BillESC and see if he can help with the replacement of a portable dimmer pack.
     
  9. JD

    JD Well-Known Member

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    Some footnotes for all:

    Very few dimmers use active current limiting. Back in the 70s/80s, some TTI dimmers actually had a current monitor loop that would inhibit SCR firing if too much voltage drop occurred across the choke. Shame they were so ugly looking ;)
    About the only thing that limits current in most dimmer circuits these days is the drop across the wire between the dimmer and the short. This is why some survive and some don't. The closer the short, and the heavier the wire, the greater the chance the Triac / SSR / SCR / IGBT goes bye-bye!

    If you have a direct short and use the proper gauge wiring then the device will often fail before the breaker kicks or the fuse blows. Some dimmers use "silver sand" or "rectifier" fuses that are designed to fail real fast. They are much larger then the expected load (20 amps for 1k dimmer) and are used in combination with standard fusses or circuit breakers which are rated at the normal current output. As to if this works, well, the opinions are mixed.

    Breakers and fuses are good at stopping general overloads before damage is done. On direct shorts, they are good at preventing a fire, not as good at protecting the switching device. Lamp flashovers can fit in either category, but usually a good dimmer will survive.
    This is one case where an ounce of prevention is worth a pound of cure. Always inspect your cables, connectors, and lights for possible shorts.
     
  10. avkid

    avkid Not a New User Fight Leukemia

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    TTI you say?

    [​IMG]
     
  11. JD

    JD Well-Known Member

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    Ha Ha! Yes! That be them!

    Unless that is an old photo, it sure says a lot that at age 30+, those guys are still working! (They sure look in good shape.) Remember, we often talk about "old failing dimmers" that were built in the 90s !

    I used EDI myself, with its odd 2-7.6v control. EDI used two 65 amp SCRs for a total of 135 amps of full wave RMS rating for its 2.4k dimmers. Never lost any despite a lightning hit and a house electrician that once tied them into a 480 line. EDI did not use current limiting in the design. I always admired TTI for doing so.
     
  12. avkid

    avkid Not a New User Fight Leukemia

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    The photo is about two months old.
    We use them with a custom A/D converter and a first generation LanBox controlled by a Mac Color Classic.
    :)

    Boy does it get some funny looks.
    :lol:
     
  13. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    I'm disappointed Phil! I wanted to read:
    "We use them with a custom A/D converter and an EOS." :)
     
  14. avkid

    avkid Not a New User Fight Leukemia

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    Psh... we roll old school.
     
  15. DimmerDotCom

    DimmerDotCom Active Member

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    Ha! Old stud mounted SCR dimmers can last for decades because they are so overbuilt. The firing cards are what fail over the years as the electrolytic caps dry out. If your dimmer uses 65A SCR's and they blow one day, spec a change to 85A or even 110A SCR's for added robustness.

    TTI dimmers may be ugly, but way easier to work on than CCR200/300/600 dimmers. I just serviced 75 TTI's. Only 3 bad dimmers after 40 years. Better than walking on a studio lot and seeing every Sensor rolling rack with a spare CEM and a half dozen dimmer modules sitting on top. That forced cooling trend in dimmers is crap for robustness but good for reduced size.

    WARNING: if you think you want to service your own stud mounted SCR dimmer watch out! It is dangerous as one heatsink will be at line potential and the other will be at the load potential. ZAP!

    Maurice Garcia
    dimmer.com Home Page
     
  16. JD

    JD Well-Known Member

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    Yea, most of the TTI that hit my bench was due to ring cracks from vibration on the road. First thing I would do is flip the mods and go over all the pads where the leads would break from the pad before I even flipped on the power. Often, by the time I flipped on the power, the module was working fine!

    In a theater setting, they will last about... forever... until the caps dry out. (And that's a pretty easy fix too!)

    Total agreement on fan cooled dimmers. Drags all that junk in there. Still, this is now the world we live in!
     
  17. FMEng

    FMEng Well-Known Member Fight Leukemia

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    Let's correct our terminology here. Electricians wire buildings. They do not repair electronic equipment, and they don't have the training to do so. An electrician can identify whether a problem is the wiring or the dimmer, but the dimmer is a black box to him or her.

    Electronics technicians and service technicians have the tools and training to repair certain kinds of electronic equipment. They might be qualified to repair a dimmer if that is their specialty, but they do not touch building wiring. Technicians are found through the manufacturer or dealer for the brand of equipment involved.

    Also, I can't help but notice the drink bottle perched on top of the dimmers in the picture. Don't do that! Sugary liquids and electronics do not mix. A spilled Coke will kill things instantly.
     
  18. FMEng

    FMEng Well-Known Member Fight Leukemia

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    Yes, fan cooling is the scourge of my existence. With fan cooled systems you need to be observant to notice when (not if) the fans have failed and then replace it immediately. Bearing noises can give you fair warning of a failure. Often times, the equipment will continue to work normally with a dead fan, but it is slowly cooking itself to death. The long term reliability will be compromised.

    At least finding replacement fans and doing the work is usually not too challenging.
     
  19. church

    church Active Member

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    have to agree with FMEng, very few electricians have the ability to diagnose and repair a faulty dimmer module. You really need a service tech familiar with dimmers. However having said that a good electronics technologist or technician can usually repair mant things they have not seen before especially if they work as a development tech in support of design engineers. The struggle is that you may have to pay for their learning curve.

    When you find someone who can repair dimmers etc keep in contact because anyone who can fault find and repair circuits at the componen level instead of just replacing boards is a very valuable find.
     
  20. panandtilt

    panandtilt Member

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    Does not appear to be a thyresistor problem but rather an gate trigger issue.
    If the chokes are buzzing when a load is applied then the thyresistor is being partially triggered and the choke is sinking the excess current. Depending on what type of choke it is I would not recommend painting or sealing it with silicon or similar substance.
    As stated in other post I would recommend that a qualified service technician troubleshoot the issue.
     

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