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Three dimmers won't turn off

Discussion in 'Lighting and Electrics' started by Charc, Feb 10, 2008.

  1. Charc

    Charc Well-Known Member

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    Okay, so I have an issue with circuits/dimmers 99, 100, and 109. (99 and 100 are in the same module).

    These dimmers appear to be sending out 100% intensity all the time. I tested these circuits with my gamchek with the architectural panel off, but the board on. I only had one channel up though (fluorescent house-light circuits). So the racks should not have been receiving any levels for the suspect dimmers.

    My first thought was bad SCR dimmer. When they go "bad" (can't remember the correct term, "blow"?) my understanding is they no longer dim, and SCR dimmers work by stopping power, not letting power through (like sine wave dimmers, right?), so when they go "bad" they don't stop any power, resulting in 100% intensity.

    I explained the situation to the dept head, and suggested swapping the module with one of our unused positions (over 15 2x20A modules dedicated to FOH that are hardly used) to determine the issue is in the specific module. She said we shouldn't settle for broken gear in a relatively new install. She sent a work note along to the school's in-house electrician.

    I wasn't informed of wether or not he was coming, or when. But he came, found no problem, and it appears maintenance is none too thrilled over wasting time on a false-alarm.

    The dept head confessed to me the other day (in a slightly accusatory tone) that she didn't really understand what I was saying, and that she sent the note along to maintenance, which had come and determined everything was fine. She did tell me to contact maintenance myself, and handle any issue (if it exits).

    I double checked my results, and it appears that there is in fact an issue with the dimmers in question. There are a couple more steps I could trouble shoot, but I really think the easiest thing to do at this point is to swap the modules. I've checked the SD80sv manual, and it's a simple enough task. (Greenia, Gaff, Derek, What Rigger?, Soundlight, Eboy17, oh and Phil, please don't jump on me for that comment.)

    I think at this point the best thing for me to do is to type up a quick explanation of what the issue is, explain my tests, explain the module swap procedure, request to meet with the in-house electrician to explain the problem, and forward this document to the head of maintenance along with an apology for the misunderstanding last time.

    So after that long winded explanation, here's my question to the booth:

    Is a "bad" SCR dimmer the most likely issue? What are other probable issues (Perhaps the dimmers were set to panic for some reason, and panic mode activated? Perhaps when patching in fluros, these channels were set to constant-on?)? What information on SCR dimmers should I include in the document? Will I die a violent death from a module swap, Derek? :rolleyes:

    Thanks for your time and attention,
    Charlie
     
    Last edited: Feb 10, 2008
  2. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    That was more than one question, so I'm going to give more than one answer. In no particular order, just to make it harder for you. When either of the two SCRs fails in a dimmer, and in fact you actually have SSRs {which contain two SCRs, [in fact you may have a dual SSR, which contains 4 SCR's] [The original SCR looks much like a spark plug. An SSR looks like a square hockey puck, (what, making ice again?)]}, the dimmer can appear to be stuck ON OR stuck off. It sounds to me as though yours have appeared to have "gated on" if their output stays at full, when neither the Strand300, nor the architectural system, nor the "CEM™"-(sorry for using an ETC term, but I don't know what modern CD-80 Supervisor racks call them) is not telling those dimmers to be at full.

    Whether or not a High School student should be permitted to swap dimmer modules has been debated here previously. [edit: My opinion, (and I am NOT qualified to offer advice...Hire a professional...etc.)...is that swapping a dimmer module is less dangerous than changing a screw base A-lamp, or plugging in an extension cord.] Your instincts (or what you have learned here) are spot on. Module swapping would be my first step in troubleshooting. Unfortunately, since you appear to facilities as to have previously "cried wolf," it may be difficult to get a building engineer to put down his coffee and donuts, and leave his soap-opera to come to your dimmer room so you can suggest an industry-strandard trouble-shooting procedure.

    As to your drama dept. director's desire to make someone else fix it, the system is out of warranty, is it not? SSRs cost something nominal (under $50?), and changing them requires more mechanical than electronics skill. Not that I'm suggesting you do it, but don't ignore the thermally-conductive compound when changing SSRs.

    However, my suggestion is to rip out the dimmers and install two racks of ETC Sensor™ (but not Sensor+:(), and perhaps an Ion while you're at it. I just worked with a 48way Sensor Rolling Rack with a 1993 serial number, which has most likely been all over the world many times, and it worked flawlessly, and even has slots (just like spare matte knife blades) for a spare CEM and two spare D20 modules).

    I suspect one of CB's members could assist you in preparing a bid for console, dimmers, and fixtures. The more you buy, the less expensive each becomes.
     
    Last edited: Feb 11, 2008
  3. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    Charc, Walk up there, turn the breakers off before you pull. Grab that handle and pull with all your might... not really... then with a mighty shove put all the bad modules into circuits that are regularly used... houselights perhaps?... so that this time they can find your bad SCR's. Eventually your house electricians will figure out that they don't know how to fix them and you'll have to send them to the local theater shop. In my experience they cost about $100 per circuit to get fixed.

    The only safety thing is don't be stupid and reach inside the rack while the module is out to have a look around... You WILL die. Just swap them one at a time and you'll be perfectly safe. I've been told that you don't really even need to kill the breakers first but I always do.
     
  4. Charc

    Charc Well-Known Member

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    I'm afraid I have to disagree:

     
  5. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    GaffMark:
    A) You forgot that Charc doesn't access to the dimmer room.
    B) The facilities people will get real angry after Charc purposefully leaves all his houselights ON and they burn out. Not to mention that someone may want a blackout before Facilities gets around to looking at the dimmer problem.
    C) I had better never catch you moving modules around without labeling and documenting what you have done so as to aid in further troubleshooting.

    I hope your ClassicPalette gets a virus.:twisted:
     
  6. JD

    JD Well-Known Member

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    Don’t you just love it when they come out and tell you “nothing is wrong” !!!

    Now, on to your question. Yes, probably bad SCR as the failure mode turns them into a piece of wire! (Always on.) The failure is not intermittent in nature, once it happens, it’s a done thing. So, if for some reason they “unlatched” for even a second, you could rule that out. Still, it’s good to check out other options. Most dimmer packs use a microprocessor to control the SCRs. The micro basically reads the DMX info and then calculates how many clock ticks to count from the zero voltage point to the time the SCR should be gated on. The only reason this is important is that micros crash, so we want to insure that a hard reset is done before you call for surgery. With the board DMX disconnected, power the module down for 30 seconds. Sometimes a micro is used to control several channels, so we want to make sure that the micro is powered off, so I would suggest doing it at the main panel feed. If the channels still come on, we can almost be sure that we have SCR failures. I say almost because some data (such as idle set) are stored in non-volatile RAM. (eeprom) This would not reset with a “hard reset.”

    So, with the DMX disconnected and the power cycled, we can be sure that the board is not telling the channels to stay on, and it’s time to have the mods switched. Good luck.
     
  7. Charc

    Charc Well-Known Member

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    *Gulp* main panel hard reset? If it is a microprocessor issue, will that be retained in the module in question if it is swapped, or the position in question? If it's a bad module, would opening the module make the condition apparent (Charring, broken connector, etc?)? Does opening the module void warranty?
     
  8. JD

    JD Well-Known Member

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    Depends on the system. I have seen systems that have only one processor for a 12 channel pack, I have also seen systems that have fully contained modules with each channel having it’s own. (Guess which costs more, and which one was real cheap ;) )

    Generally, when an SCR goes, there is no visible sign of failure. And depending on the system, opening the module would void it’s warranty, although many use open frame modules so there is nothing really to open once the module is out of the rack. In any case, there probably is nothing to see as the devises (SCR, Triac, SSR, IGBT, GOT) all fail internally.
     
  9. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    You're not, I don't think, opening the dimmer module, you're just pulling the "drawer" completely out and looking at it. But you most likely won't see anything suspicious. Here's a non-helpful informational link. Even if your system IS still under warranty, I doubt that this would be a warranty repair unless less than one-year old. Only once have I worked with a brand new dimmer installation, I think, and I didn't have to replace SSRs until 2 or 3 years out.

    If, when one swaps modules, the problem follows the module, it's a bad module, easily repaired by a competent individual or one's friendly local lighting shop. Since it is three dimmers out of 192, I wouldn't even bother with a hard-reset. As was mentioned in the other thread, swapping modules is less hazardous than operating a 400-800A disconnect. Ignorant question: is there a "reset" button on the Control Module of each rack? Are both of your racks fully populated; and are all slots wired? (I.e., does every circuit 1>192 appear somewhere in the stage or auditorium?)

    How about this, page 114 of the CD80SV manual says exactly what we've been telling you.
     

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    Last edited: Feb 11, 2008
  10. Charc

    Charc Well-Known Member

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    One slot has a faux front, so I'm assuming that's "not populated". Otherwise the racks are fully populated. I do believe that everything shows up in the theatre, it's hard to tell though, because house-light sconces aren't labeled.

    Reset button, I think so, but I need to check.

    Yea, I'd just swap a module.

    The "opening a module" bit was in reference to JD's disconnect comment. I was looking for alternatives to working with hundreds of amps of live power. If there is no visible failure from a bad dimmer, then the plan is to just swap the module, easiest next step. I also think it's the most likely. I may have the in-house electrician though, because if anything gets f'ed up it's my head on the chopping block.
     
  11. Grog12

    Grog12 CBMod CB Mods Premium Member

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    Charc...do this for me...because I'm an anal retentive screw ball. Anything in your theatre that might control the dimmers...shut them off! Your board, your architectuals, anything that might control them.

    Are the dimmers still outputting power?

    If they aren't problem solved you have a screwed up patch somewhere.

    If they are...you have a larger issue which might be said SCR problems.
     
  12. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    Sorry... forgot about the no access student thing. That's actually what I did as a teacher getting ignored by the custodial staff. If they can't turn the lights off it'll get their attention and they'll have to figure out how to fix it.

    (It may not get a virus but it's hard to tell if I don't get decent training.)
     
  13. Charc

    Charc Well-Known Member

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    To chime in, it's not because I'm a student. The dimmer room was originally keyed under a different dept. The theatre dept requested it be keyed as a Z key. They had a ZM tumbler deal lying around so they threw that guy in. The spare key I've "borrowed from the dept head" 24/7 for the last 12 months is her spare key, which happens to be a Z9. She can't get another ZM though, because then there'd be questions asked about where her key disappeared to.

    So if I want to get in, I just have to borrow the dept head's, TD's or maintenance guy's key.
     
  14. soundlight

    soundlight Well-Known Member

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    As long as you don't reach in to the racks at all (usually obvious, but I always state the obvious), swapping modules isn't nearly as dangerous as plugging in a stagepin connector. When we clean modules at my theatre, we simply take them out one by one, while the rack is live, and blow them out with the air compressor. Then put them back in, one by one. Of course, we make sure that there is no load on them while we are cleaning, and turn the breakers off before removing them, but nothing else...just pull out the module, clean it, and return it to its slot. The power connections are in the far back of the rack, so you won't come anywhere near the high-amperage power. So, if you can get facilities in there, you have an easy way to figure out if it's the dimmer module or something else.
     
  15. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Might I add that with ETC Sensor, Colortran D192, ENR, and i-series, I'm not sure you could get your hand in there to touch any live contacts if you wanted to, as long as you pull only one module at a time.

    If I were pulling all the modules for cleaning, even one by one, I would LOTO the entire rack, then one needn't even switch off the breakers on each module.

    However, I do have an issue with you using an air compressor to blow out your dimmers, [user]soundlight[/user.] And do you do this blowing out in the dimmer room?
     
  16. soundlight

    soundlight Well-Known Member

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    Compressor is at low PSI to not damage electronics. And the dimmer room is located through two doors through the back of the shop downstairs, so we just take the modules out in to the shop and clean them. No dust left in the dimmer room. Is there any other problem with this method?
     
  17. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Air compressor air is not "clean air," so you are covering your components with microscopic droplets of oil. Might as well just put a DF-50 into the air intakes. The oil will actually attract dust and debris. Just my 2¢.

    And carrying each dual module "through two doors through the back of the shop downstairs" and back must get tiresome. It would make more sense to me to LOTO the rack, remove all the modules, clean them, then mix them up so each gets exercised equally (the cyclight dimmers never work as hard as the FOH dimmers, as some shows don't use the cyc). And while you're at it, be sure to remove the winter air in your car's tires and put it summer air. Do the reverse in the fall.

    Also note that ETC recommends vacuuming Racks and Modules as necessary, rather than blowing the dust away.
     
    Last edited: Feb 11, 2008
  18. soundlight

    soundlight Well-Known Member

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    If it wasn't an oil-free compressor then I'd be able to go with that argument. And it's a mere 8 steps out to the shop, but you pass through two doors in those five steps. Grab a few modules, walk out, blow them off, walk back in. And they do get shuffled in the racks. It wouldn't be practical to take out 384 dimmer modules and put them carefully in to boxes, put them on a hand truck, walk them all 8 steps out to the low-particulate side of the shop, and blow them all off, then take them all back in.
     
  19. gafftaper

    gafftaper Senior Team Senior Team Fight Leukemia

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    I've always heard that you should never blow your dimmers clean always vacuum only. I'm also not a fan of blowing dust around just to be doing it... even if it is outside. Thus the vacuum makes sense as it keeps the dust confined.

    Soundlight, You could roll the shop vac into the dimmer room and clean them on the spot.
     
  20. TimMiller

    TimMiller Well-Known Member

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    blowing always removes better than suction. When i go out to clean dimmers and such i use an air compressor set at about 30 psi, and a shop vac with a nice large opening to help suck the dust.

    Now back on topic....
    Simply turn off the breakers on the dimmers. Loosen the holding bar if there is one, some cd80's had them others didnt. Pull the module out, it wont be easy to pull out, they are in there good. (on one of our road racks it uses CD-80 modules, and i have to hold the rack with my feet then pull on the module with both hands. Its not an easy task.) To reseat the modules i slam them back into the rack. If i dont it will no reseat correctly, and you will know it if it doesnt. The module will not be all the way in the rack. If you would like i can take some pics of what it looks like when you pull a module out of a CD-80. There is nothing to it. I can also take pics of what it looks like inside the module.
     

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