# Channel Stuck?



## Synchronize (Mar 16, 2008)

It's quite odd. Channel 15 at my highschool is like possesed. Sometimes, it would just come on in the middle of the night. The wall controls would show the channel as off, but sure enough it was lit up. It would always be off by morning again. But, just recently, it decided not to go off. We were cleaning up after play practice one day, we just turned off the light board and channel 15 lit up. We turned the board back on and it showed no power going to it so we just packed everything away and expected it to be off by morning. Well it wasn't, and wasn't the day after, or the day after that. It was on for 5 days straight and never turned off. We finally turned the light board on, got the big ***** ladder out, and unplugged the light, then replugged it back in. It was off, so we turned on the channel on the light board. It turned on no problem. When we went to turn it off the board showed it as 00 but it looked as though it only backed down to about 70. We tried plugging the fixture into other channels and other fixtures into channel 15. We deduced that it was not the lamp, but the channel. Any ideas what would cause this, or what we could do to fix it?


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## Charc (Mar 16, 2008)

Failed SSR pack resulting in the dimmer being gated on? Happened at my place. Try swapping your modules.


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## Synchronize (Mar 16, 2008)

But when its unplugged, the plugged back in, the light stays off untill activated. And once its on, then turned off, it doesnt stay full, it backs down to around 70 and stays there. Its almost as if the channel is only getting part of the signal.


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## David Ashton (Mar 16, 2008)

It would be unusual for an ssr to be intermittent, usually they blow "on" and stay on.My guess would be a module electronics fault.There is no way it could ever be a lamp fault, it would seem the module is accepting the up signal but is not responding to the down signal, nothing to do but send the module back for repair.


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## Synchronize (Mar 16, 2008)

By module, do you mean the rectangular box with four recepticals in it? Sorry, I know I'm a total newb at this. Sad part is, I know more about it than anybody at my school .


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## David Ashton (Mar 16, 2008)

I can only give you a general assessment of the fault, you should not attempt to go any further to fix this problem, it is dangerous to go into dimmer racks unless you know exactly what you are doing, please pass on the information that it is almost certainly a fault on ch 15 dimmer module and have a technician/electrician deal with it.I fully endorse letting students get involved with tech work and it may be useful to watch how to do it but do not at this time do it yourself.


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## Synchronize (Mar 16, 2008)

So how would I even go about finding somebody to do that? The maintinance dept doesnt know anything about it.


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## Charc (Mar 16, 2008)

I'll admit I might not have read all of that first post, hence my SSR comment.


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## Charc (Mar 16, 2008)

David, just noted your post about intermittence. I will note that a had an issue like this, but not replicate-able, just random. It makes me thing maybe this is a data error, levels being sent? Something? It's 3 AM and... yea, sorry I'm of no help.


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## gafftaper (Mar 16, 2008)

Sync... if your school has an electrician he/she can get parts to fix it, but in my experience they usually don't want to mess with this stuff. You probably just need to have your local theater shop repair it.

Tell us a little more about the dimmer rack. We are assuming you have a dimmer rack that looks something like this. A series of boxes with circuit breakers on the front? The modules may also be short and wide and look more like drawers than boxes like this. It would be really nice if you could post a picture of your rack as we can tell you exactly what you have. Or if you look around to find a brand and model that would be great too. 

As David said, messing around inside a rack is an easy way to get yourself killed. I've let students work in my racks but only when a) I'm in the room supervising and b) the power is locked off. So I want to stress that the ADULT in charge of this at your school is the one who needs to take care of this. What they need to do is take the dimmer out of the rack and take it to your local theater dealer and have them repair it. You can have the dealer come to you but it will cost a lot more. 

SO here's the plan to SAFELY get this fixed. 
-First as noted above, let's figure out what kind of a dimmer rack you have. 
-Second if you don't know where the nearest theater repair place is tell us what city you live in and we can help you find one near you. 
-Third have the ADULT in charge of the theater call the repair place, tell them what brand/model dimmers you have, and ask for instructions of how to remove the bad module to take it in for repair. Then that person needs to do the actual removal following those instructions. 

When you see it removed, you are going to think we are crazy and far too cautious. However, not to insult you, but someone with so little knowledge is taking a HUGE risk by messing with this stuff. Remember if you have a full size 96 dimmer/2.4k rack it is providing 230,000 watts of power and 1,920 amps... it only takes one amp to kill you. So again PLEASE let us help you determine what equipment you have and give you the information to share with the adult in charge to follow the directions of the local repair place.

Others who read this please don't post/P.M. instructions on how to remove a module. Let's keep this young tech alive long enough to learn how to do it the right way from someone who knows what they are doing.


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## Synchronize (Mar 16, 2008)

Ok so my highschool is in the middle of a corn field. Its a little country highschool with 750 students. We don't have an on-site electrician, and the teacher incharge of the drama dept is more clueless then I am. I have no clue what brand anything is, it all just looks generic. I'm in Richmond, IL 60071. I'm guessing that the nearest place is Breber Music in Elkhorn, WI. Thats what most of the stickers say on the sound equipment. The idiots that ran lights an sound befor the team we have now were complete idiots. Nobody ever thought it might be a good idea to save any paper work on any of our equipment. The highschool is about 10 years old, but believe me, we dont have state of the art equipment.

I'm going to keep assuming that the "module" of which you speak is a rectangular box with four recipticals for the lights in it. If so, why would it be the whole module if only one channel in it is stuck?


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## soundlight (Mar 16, 2008)

If you have access to a digital camera, take a pictures of the various parts of your lighting system and post them here.


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## zac850 (Mar 16, 2008)

So, everyone seems to be thinking a dimmer problem, but I'm thinking that you have some problem in your DMX line. It is not unheard of for fixtures to ghost on when the console gets shut off, especially if the DMX signal runs through various other devices (Unison system et al).

What kind of lighting console is this? Are your house lights controlled by this console, and do you have wall push-button switches around the theater to turn on the house lights? Do you have any sort of back-up console next to your main console? In short, does the DMX line do anything besides go out of your console and into your dimmers? (The DMX line is that 5-pin cable that comes out of the back of your light console and goes, somehow, to the dimmers to control them).

When the lighting console is on, do you ever have this ghosting problem? If channel 15 is ghosting, and you turn the console on, does channel 15 go off like the console tells it to?

If you answer no to question 1 and yes to question 2, the easiest solution would be to just turn the dimmers off when you turn the console off. There should be a large switch on the front of the dimmer rack, just flip it to the off position. No power, no ghosting light. It doesn't ghost when the console is on, so no worry during shows.

If not, well, let us know and we'll figure it out.


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## Synchronize (Mar 16, 2008)

My original post answers most of your questions.


Synchornize said:


> It's quite odd. Channel 15 at my highschool is like possesed. Sometimes, it would just come on in the middle of the night. *The wall controls would show the channel as off*, but sure enough it was lit up. It would always be off by morning again. But, just recently, it decided not to go off. We were cleaning up after play practice one day, we just turned off the light board and channel 15 lit up. *We turned the board back on and it showed no power going to it so we just packed everything away and expected it to be off by morning*. Well it wasn't, and wasn't the day after, or the day after that. It was on for 5 days straight and never turned off. We finally turned the light board on, got the big ***** ladder out, and unplugged the light, then replugged it back in. *It was off, so we turned on the channel on the light board. It turned on no problem. When we went to turn it off the board showed it as 00 but it looked as though it only backed down to about 70*. We tried plugging the fixture into other channels and other fixtures into channel 15. We deduced that it was not the lamp, but the channel. Any ideas what would cause this, or what we could do to fix it?



We never had the light go on while the board was in use prior to it staying on for 5 days straight. Then again, how often do you use a light board in a highschool? 6 weeks a year? It never came on in the day either, always at night. Yes, the DMX runs through multiple wall pannles. All of them show that it is off. I dont know in what order it runs throught the pannels but all I know is that when you turn the board on the board takes over the wall pannels. It doesnt matter what you do on the wall, the lights only take commands from the board.


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## derekleffew (Mar 16, 2008)

Based on your location, your system was most likely sold and installed by Grand Stage, DesignLab Chicago, or Chicago Spotlight. And you're not far at all from the factory of one of the two best lighting companies in the world, ETC. Find "the dimmer room" or where ever there's a rack like gafftaper posted. There'll be a nameplate on it, somewhere.


> I'm going to keep assuming that the "module" of which you speak is a rectangular box with four recipticals for the lights in it. If so, why would it be the whole module if only one channel in it is stuck?


 No, that's the outlet box; the actual dimmers are in a room somewhere, or maybe in a corner backstage, in a rack. Since you have wall panels, you have a fairly sophisticated system. Do your panels look like the attachment below? 

Take and post pictures, and we'll help you identify whom to call.


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## Synchronize (Mar 16, 2008)

Yeah, that is the type of dimmer rack that we have (just with a lot more dust).

As for the wall pannels, I think that one looks similar, the other two are different. I'm going to see if I can get into the school today to get some pictures. If not I'll have them tomorrow.


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## JD (Mar 16, 2008)

I have actually run into a SCR pack (two SCR's in same device but not SSR) that did that! It was on an EDI scrimmeret. (spelling) Anyway, would come on at random, but you could clear it by unplugging the load for a second. Had me scratching my head looking at control problems, but that odd reset gave it away. Changed the device, everything was fine. That being said, I would STILL think along the line of some control problem first! (The other 99 times I've run into things like that, it was always control!)


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## Synchronize (Mar 16, 2008)

Ok, so I havent been able to get into the school yet, but I am almost 100% sure that all of the equipment is made by Lehigh. This is what our wall controls look like. The white (kind of pink looking one, but they are white in our school) one in the very back is what the one in the light booth and backstage look like. The black one in the very front is what the one in the auditeria lookes like. The dimmer box is like the one that gafftaper pointed out, but I'm pretty sure its made by Lehigh. This is our light board, just a much newer, nicer version. Ours runs Windows '95, is 24/48, and only has one video output; otherwise it's pretty much the same. I'll still get pics of all of our stuff tomorrow.


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## Charc (Mar 16, 2008)

Synchornize said:


> Ok, so I havent been able to get into the school yet, but I am almost 100% sure that all of the equipment is made by Lehigh. This is what our wall controls look like. The white (kind of pink looking one, but they are white in our school) one in the very back is what the one in the light booth and backstage look like. The black one in the very front is what the one in the auditeria lookes like. The dimmer box is like the one that gafftaper pointed out, but I'm pretty sure its made by Lehigh. This is our light board, just a much newer, nicer version. Ours runs Windows '95, is 24/48, and only has one video output; otherwise it's pretty much the same. I'll still get pics of all of our stuff tomorrow.



With special attention to dimmers.


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## Synchronize (Mar 16, 2008)

Lol, I guess its lucky that I found THE key to the dimmer rack yeterday.  I dont think that the building manager even has a copy.


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## STEVETERRY (Mar 16, 2008)

derekleffew said:


> Based on your location, your system was most likely sold and installed by Grand Stage, DesignLab Chicago, or Chicago Spotlight. And you're not far at all from the factory of one of the two best lighting companies in the world, ETC. Find "the dimmer room" or where ever there's a rack like [user]gafftaper[/user] posted. There'll be a nameplate on it, somewhere.
> No, that's the outlet box; the actual dimmers are in a room somewhere, or maybe in a corner backstage, in a rack. Since you have wall panels, you have a fairly sophisticated system. Do your panels look like the attachment below?
> Take and post pictures, and we'll help you identify whom to call.




Who's the second best lighting company in the world?



ST


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## Charc (Mar 17, 2008)

STEVETERRY said:


> Who's the second best lighting company in the world?
> 
> ST



These guys, forget Vari*Lite!

Edit: P.S. ST, I think they are shipping a newer more advanced ERS. As VP of R&D, you may want to look about not loosing to the competition!


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## gafftaper (Mar 17, 2008)

Very clever post Charc! 


Synchornize said:


> I am almost 100% sure that all of the equipment is made by Lehigh.


We may have just found out what's wrong. If your system is all [-]Crap[/-] Lehigh, the idea of ghosting or some sort of DMX problem is an interesting possibility.

Sync, get a picture or the brand/model of your light board too.


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## Synchronize (Mar 17, 2008)

Took the pictures as requested. The board is made by Lehigh. Its called the Millenium Controle Consol. Its the board I posted in the other link, just an older version.

The builiding manager is looking into getting me wiering diagrams, paperwork, basically anything that has to do with the system.


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## avkid (Mar 17, 2008)

You need to have that cleaned rather quickly.


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## Synchronize (Mar 17, 2008)

Like I said, I JUST found the key for it. And before yesterday, I didnt even know what it was. Just use a shop vac, right?


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## Charc (Mar 17, 2008)

Oh wow, seriously?!

Get maintenance in there to completely clean that dimmer rack. Make sure they're checking out all the fans/filters as well.


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## Charc (Mar 17, 2008)

Synchornize said:


> Like I said, I JUST found the key for it. And before yesterday, I didnt even know what it was. Just use a shop vac, right?



I'm assuming the inside is crap too. Seems to me like every module needs to be removed and cleaned. This discussion came up recently, try a quick search.


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## Synchronize (Mar 17, 2008)

Yeah... 8 year old building and I'm pretty sure that today was the first time its ever been opened. As for regular maintenace, what should I do?


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## derekleffew (Mar 17, 2008)

The pictures really helped. _edit: <info regarding cleaning deleted>_

Lehigh is what we refer to as a "second (or third) -tier" manufacturer, and I don't think many of us have experience troubleshooting such systems, so if the problem persists, your best chance at solving the problem will be to give one of the Chicago vendors above a call, or contact Lehigh directly to see whom they recommend. 


> If you're still unable to find an answer to your questions, please contact Lehigh directly by phone at 610/395-3386 or by email at [email protected].


Good luck!

edit: This User's Guide is for a newer model than yours, I suspect your dimmers are the DX1, but may still prove helpful.


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## avkid (Mar 17, 2008)

Synchornize said:


> Yeah... 8 year old building and I'm pretty sure that today was the first time its ever been opened. As for regular maintenace, what should I do?


Don't touch it.
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It may be too late to prevent damage at this point.
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Call in a professional lighting company, or if all else fails your local audio repair guy.
-
After you get it fixed:
You should be keeping the area around it clean, and vacuum around the fan openings(make sure to prop the fan so it doesn't move) whenever you remember.
(make sure the power is off before you do that)
-
If it has filters, change or at least tap them out(outside please) maybe once a month.


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## Charc (Mar 17, 2008)

Derek, I don't know if the OP should be handling that much power, even in a disconnect.

Why isn't he pulling out modules too? One at a time, breaker off, clean, back in, no power to worry about.


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## derekleffew (Mar 17, 2008)

charcoaldabs said:


> Derek, I don't know if the OP should be handling that much power, even in a disconnect...


 _edit: <deleted reference to NFPA 70E>_ The complete specifications for proper LockOut/TagOut procedures are outside the realm of Control Booth.



charcoaldabs said:


> ...Why isn't he pulling out modules too? One at a time, breaker off, clean, back in, no power to worry about.


Considering the controversy surrounding students removing dimmer modules, I felt it best not to suggest that course of action. Again LOTO is beyond Control Booth.

I was remiss, however, in NOT instructing the OP to perform dimmer cleaning ONLY under the supervision of a staff or faculty member.


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## avkid (Mar 17, 2008)

derekleffew said:


> in NOT instructing the OP to perform dimmer cleaning ONLY under the supervision of a staff or faculty member.


I covered that.
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I honestly think an electronics tech of some type needs to examine it.
-
I've seen "frozen" clogged racks, and it isn't pretty sometimes.


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## gafftaper (Mar 18, 2008)

I'm thinking a good way to help solve this would be for one of us to talk directly with your head custodian/maintenance/electrician/drama teacher... whoever the adult in charge of the space is. Again not to insult you Sync, but there is serious danger involved in this much power and an untrained student should not be doing the work. Why don't you send either Derek, AVkid, or Me a private message with the name of the adult to contact at your school, phone number, and good time to call. Whoever you contact will call that person and explain the process of safely giving the dimmers a full cleaning.

Cleaning alone may fix the problem or there may be further issues.


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## porkchop (Mar 18, 2008)

Congratulations Sync you've found one of the 23461 way to kill yourself if you don't know what you're doing/ don't have proper supervision in a theatre. There is truly an amazing amount of power going into your dimmer rack and it doesn't take a whole lot to hurt yourself. At very least you need to be supervised by someone who knows what they're doing. You've kind lead onto the fact that you may not have anyone working at your school that is really qualified to mess with your dimmer rack. In that case you DEFINITELY need to take gaff's advise as send this to people in higher places.


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## Synchronize (Mar 18, 2008)

Well here's the deal. I talked to the building manager today and he said that he'll help me out in any way possible. Thursday were going to shut off the power to that whole thing, remove the modules, clean every thing out, and replace everything. I'm not 100% sure that he knows the system, but if the powers off the powers off, right?


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## Charc (Mar 18, 2008)

Synchornize said:


> Well here's the deal. I talked to the building manager today and he said that he'll help me out in any way possible. Thursday were going to shut off the power to that whole thing, remove the modules, clean every thing out, and replace everything. I'm not 100% sure that he knows the system, but if the powers off the powers off, right?



Lock-out *and* tag-out.

I think the way we left it from our previous discussion is it is probably best for your to carry your modules outside, into a fire-tower, or away from the rack, and use a compressor to blow all the dust off. But definitely read that thread through, you want to make sure your compressor is calibrated to not wreak havoc on the modules! It also may be worth your time to rotate the modules, the less-used ones to more used locations. Blow off the rack too, the fans, whatever.


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## porkchop (Mar 18, 2008)

I can't say it enough HUGE AMOUNTS OF ELECTRICITY!!!!!! If you really wanna do this yourself at least get a conversation going with a CB vet. And get the proper LOTO protocol from the manufacturer. Also I can think of atleast one thread that give a lot of good info of cleaning dimmers (I think it was charc's about dimmers being stuck off)


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## Synchronize (Mar 18, 2008)

Yeah, I read it and I'm pretty sure that it was determined that a compresser would blow all sorts of pnumatic oil all over the equipment. Charc says a calibrated compresser. By that I guessing you are refering to the oil issue. Yes well if you remember I'm in a little school that probably has like a pancake compresser that they use to fill up the plow trucks tires... so without having a decent compresser shop vac right?

If somebody wants to contact me on MSN to go into more detail its [email protected].


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## Charc (Mar 18, 2008)

Brett, he will have the building manager there conducting the work, he says.

When I did the stuff with my dimmers I had 3 maintenance guys with me... then again it was the rally point for discussing in detail the various issues in the theater.


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## porkchop (Mar 18, 2008)

Ok so after making it red and underlining it I decided to do what I do best...numbers.

Pic 2 shows 17 Modules. I'm going to assume that they are 2.5k W dimmers (I would say the most common rating, but by no means the only one). That means that you have 17 x 2500W going into the rack. Thats 42,500 Watts possible, thats something on the order of that amount of power going through a low power overhead line.

Just one dimmer (if its in fact 2.5k W) would have 120 V and 20.83 Amps (2500W/120V). Now if I had to make an approximation of the amount of power it would take to kill a person, I'd say something like 1 Amp at 120V. Yah that's A LOT less than 20.83 Amps.

In one last point, every modern dimmer rack that I've dealt with has 2 dimmers per module. If thats the case then you have the potential for doubt the power going into the rack.

Now do you understand why we're really touchy about you playing around inside the rack, and why the company has very specific protocols for powering down your dimmer rack so that it can be worked on?


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## Charc (Mar 18, 2008)

porkchop said:


> Ok so after making it red and underlining it I decided to do what I do best...numbers.
> Pic 2 shows 17 Modules. I'm going to assume that they are 2.5k W dimmers (I would say the most common rating, but by no means the only one). That means that you have 17 x 2500W going into the rack. Thats 42,500 Watts possible, thats something on the order of that amount of power going through a low power overhead line.
> Just one dimmer (if its in fact 2.5k W) would have 120 V and 20.83 Amps (2500W/120V). Now if I had to make an approximation of the amount of power it would take to kill a person, I'd say something like 1 Amp at 120V. Yah that's A LOT less than 20.83 Amps.
> In one last point, every modern dimmer rack that I've dealt with has 2 dimmers per module. If thats the case then you have the potential for doubt the power going into the rack.
> Now do you understand why we're really touchy about you playing around inside the rack, and why the company has very specific protocols for powering down your dimmer rack so that it can be worked on?



I note 17 modules with 4 breakers per module. I believe the most common dimmer is 2.4kW. We may be looking at a lot more power if that is ((17x4)2.4kW)=A ; but I don't know if those numbers are correct, just making random guesses.


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## porkchop (Mar 18, 2008)

My point is that as previously mentioned the building manager may or may not know any more about the system that our new friend Sync. That in mind even if the building manager knows about electricity and it's dangers. He/She maybe not realize exactly what goes into a dimmer rack. I'm not saying you have to LOTO to clean a dimmer rack. I'm just saying make sure you have a talk with someone that has a good idea (keywords) exactly whats going on so you can stay safe.

EDIT: maybe 2.4k is right, it doesn't really matter. The point was to give round numbers to show why dimmer racks need to be respected.


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## Charc (Mar 18, 2008)

porkchop said:


> My point is that as previously mentioned the building manager may or may not know any more about the system that our new friend Sync. That in mind even if the building manager knows about electricity and it's dangers. He/She maybe not realize exactly what goes into a dimmer rack. I'm not saying you have to LOTO to clean a dimmer rack. I'm just saying make sure you have a talk with someone that has a good idea (keywords) exactly whats going on so you can stay safe.



Oh, I'm in agreement. But presumably the building manager will be handling the power... if they can't handle it... then why are the building manager? Oh well, they won't be for much longer...


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## porkchop (Mar 18, 2008)

charcoaldabs said:


> Oh, I'm in agreement. But presumably the building manager will be handling the power... if they can't handle it... then why are the building manager? Oh well, they won't be for much longer...



True, but if the building manager doesn't understand the power involved there could be things that are overlooked because "that isn't really important until you get to something with more power." Think about it as far as a High school goes most things use significantly less power thats what the building manager will be used to working with.

EDIT: And that "Oh well" situation isn't going to be a good one.


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## Synchronize (Mar 18, 2008)

Guys, you have to understand here, I'm no idiot. I'm the kid that gets nervous about putting a new male end on an extention cord and then plugging it in. I'm not the kid that says, "OOOOO pretty shiny copper... lets touch it." The Building Manager is getting all of the original paperwork on the system, including wiering schematics. I am also going to contact Lehigh and get the proper method of doing this. I am most likely only going to handle the modules until after they have been removed by the Building Manager. Believe me when I say I'm not going to "play" around in the dimmer rack. Electricity scares the LIVING POOP (since nice filters wern't in place for the other word) out of me. I'm no fool.

But just to let you know, I do appreciate all of your concern.


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## porkchop (Mar 18, 2008)

That's what I wanted to hear, basically I know in high school I would have just turned off the breaker and had at it, and if that had happened odds are good I wouldn't be here.


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## derekleffew (Mar 18, 2008)

porkchop said:


> Ok so after making it red and underlining it I decided to do what I do best...numbers...


Sorry, but that point is arguable.


porkchop said:


> Pic 2 shows 17 Modules. I'm going to assume that they are 2.5k W dimmers (I would say the most common rating, but by no means the only one). ...


2.5Kw dimmers exist only in countries that have 220-240VAC power. The standard in this country is the 20A, 2.4Kw dimmer, usually in dual modules.


porkchop said:


> Just one dimmer (if its in fact 2.5k W) would have 120 V and 20.83 Amps (2500W/120V).


Dimmers are rated by their circuit breaker, and you'd be hard-pressed to find a 20.83A breaker. The OP has 17 Quad modules, which I suspect are 10A, as 20A quad modules are rather rare (Kliegl and EC come to mind). This would yield a total theoretical load of (17*4*10)=680A. The NEC allows "undersizing" of incoming feeder, as not every dimmer will ever be loaded to full capacity, and the disconnect switch looks to be of 120/208VAC 3Ø Wye-connected 4W+G, 200A size.


porkchop said:


> ...Now if I had to make an approximation of the amount of power it would take to kill a person, I'd say something like 1 Amp at 120V. Yah that's A LOT less than 20.83 Amps...


From here: A low-voltage (110 to 220 V), 50 or 60-Hz AC current travelling through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 60mA.
That's 0.06 amperes, about as much as a 120V, 7 watt night-light.

Yes, electricity is dangerous and can kill, but should be treated with caution and respect, not fear. Just like a loaded gun.

The question remains as to whether a minor or non-staff member should be working around any electrical circuits, even plugging in an extension cord. That's for each venue/school district and their insurance carriers and lawyers to decide.


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## gafftaper (Mar 19, 2008)

porkchop said:


> That's what I wanted to hear, basically I know in high school I would have just turned off the breaker and had at it, and if that had happened odds are good I wouldn't be here.



Amen Brother! Preach it!


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## porkchop (Mar 19, 2008)

ok derek you beat me, but my point still stands. I didn't do much research for my numbers cause I knew that they were so big that rough estimates would illustrate my point. 2.4k is apparently the US standard, thats an oversite but still close enough to get the point across, your point about undersizing of breakers is interesting but in the realm of understanding if there's enough power in a dimmer module to kill you, the more the marrier but you'll still be fried in the end. And yes if a relitively small current passes directly trough the heart is can be lethal but I figured that 1 Amp was an easy to comprehend estimate that covered most any way that power could pass through the body, and it is still an order of magnitude lower than your estimated 10A per dimmer. Basically if I had really wanted to give exact number I would have looked harder. Yes maybe I should have done that , but I was really just trying to give a little more perspective than 
HUGE AMOUNTS OF ELECTRICITY!!!!!!.

EDIT: I do like your loaded gun simile it's very true. There are amazing things that can be done if we take our respect of electricity and put if plus knowledge to good use


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## TimMiller (Mar 19, 2008)

I'm always the one to jump head first into a dimmer rack. Yet I have accumliated knowlege from ETC and Strand, and have been working on dimmers since i was about 14. I'll work on a dimmer any day over a strobe. Dimmers as long as you lock out tag out are very safe. (lock out tag out is a practice in which you turn off the disconnect, lock it with a padlock, then tag it so it says Do not energize equipment, or do not turn on). You do have to be aware commonly you have more than one disconnect running to dimmer racks. So even though you powered off one rack there may be another one still powered up. Also they sometimes do some really strange stuff to add on non dim circuits.

Being over cautious is good. Studies have shown that the well seasoned electricans get shocked more than the younger ones, due to they become too comfortable around electricity. Honestly i have gotten shocked a few times, but it is normally in the shop when repairing moving lights and strobes due to caps not discharging. I know i have said this before on here, but never assume anything. I have never been shocked repairing a dimmer rack.

Turn off the main disconect, then turn off the breakers on the dimmers. Then remove the modules. For a very detailed rack cleaning like yours needs, after you remove all of the modules look around and find all the fans. out of safety pratice DO NOT TOUCH THE BUSS BARS IN THE BACK OF THE RACK. If you must touch them be sure to verify with a meter that they are truely off. Then blow out all the fans. Don't let the aircompressor make the fans spin or you will be putting extra wear and tear on the fans, and when you make them spin the fans actually work as a generator and back feed the circuit board in the processor module. After blowing out the fans i give them a spin by hand to make sure they spin freely. If they catch, bind, spin very little or dont even spin at all they need to be replaced. You can usually get new fans from electronic stores or industrial supply houses. You are best off bringing in the old fan so they can match it for you, or just get one from your local theatrical dealer.

Disassembling your first dimmer will be a great learning experience and a good practice of electrical safety. Just remember never assume anything is actually off. I will PM you my cell number incase you need it


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## church (Mar 19, 2008)

The message to have a qualified person do this is absolutely correct, not only does the lock out tagout procedure need to be followed but just turning off the main breaker switch for a complete dimming system can be dangerous and is considered as working on a live circuit even when the breaker box is enclosed. 

This is because you may have an arc flash hazard issue depending on the voltage, current and the supply but theatre installations tend to have large power supply capability.

This is one reason why switchgear is suppossed to be in a locked room. operating breaker switches can and often does require the electrician to wear a fire resistant clothing ranging from pants and shirt (and underwear up to special nomex suits and helmets. There are special techniques required for this to minimise injury should a flash occur.

Our electricians regularly have to put on their suits when changing fuses etc.

I know this is probably not what you want to hear or read for that matter but the shocks you get from working on an instrument on a bench are a completely different situation to what can happen when you start operating three phase switchgear handling large currents etc fed from high voltage transformers. You don't get second chances with this stuff.

I know we have all operated switchgear without thinking about this but thousands of people are injured every year in the US and Canada by these types of incident. FYI the temperature of the flash is usually 35,000F with noise levels of 125dB and a shock wave of 125 psi. The flash boundary can be anything from a few inches up to 8 feet and more. You need an engineer to analyse the specific situation, the flash hazard is suppossed to be identified on all recent switch gear installations. BTW wearing the PPE doesn't mean you will not be injured it is inteneded to limit injury to recoverable second degree burns.

So it is quite likely that the Building Manager does not have this knowledge or training because they are not supposed to be operating Switchgear.


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## Synchronize (Mar 20, 2008)

Its done. We cleaned it and it didn't solve the ghosting. Any other ideas as to what in the module could cause the problem? Is there a specific part that we could order from the manufacturer that can be installed in the module.

The first time the channel is turned on it will turn off if the dimmer swich is pushed down quickly it will turn off. After that it only backs down to about 40% and wont come down any more.


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## icewolf08 (Mar 20, 2008)

I have been holding off on posting in this thread because of a couple things. Mostly I was trying to compose some thoughts.

First off, I know that we preach safety, but most modular dimmer racks are designed such that cleaning them can be done safely and with relative ease. I know that at the moment for this thread it is a moot point (given that the cleaning has occurred before my posting), but given some of the things that have come up in this thread about cleaning dimmer racks it makes it sound like on one should be cleaning their own racks. I have seen dimmer rack disasters (luckily only resulting in damaged tools), but only when people have done stupid things.

Now, as for solving your ghosting problems, you should try swapping the position of the affected module with a working one. If the problem follows the module (i.e. some other channel than the one you said was a problem now has the problem) then you know that the module needs replacing. If the problem stays with the same output then chances are the rack controller has an issue. 

Here is a quick why this works: The modules are essentially dumb, they don't know what number they are or what they turn on and off. The rack controller takes the information from the console or architectural controllers and tells the dimmer in a given slot to turn on or off. Dimmers are controlled by their position in the rack. To wrap this up, it means that you can take the first module and swap it with the fourth and it won't change what comes on when you bring up a channel on the console.

The other thing that is worth checking (though I don't know if it is even possible with your gear) is to see if you have a dimmer profile set up for that particular dimmer either in the board or in the rack controller.


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## Synchronize (Mar 20, 2008)

Yeah, after all of your warnings, I was quite unimpressed with the "HUGE AMOUNTS OF ELECTRICITY" and the implied amount of danger. I'm pretty sure that there was more danger of getting my ID sucked into the shop vac and strangling me. I'll try switching the modules in the next couple weeks. Spring break started and I'm leaving for a cruise on Saturday. XD


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## TimMiller (Mar 21, 2008)

have fun. You may have a bad fader on your console also.


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## gafftaper (Mar 21, 2008)

Synchronize said:


> Yeah, after all of your warnings, I was quite unimpressed with the "HUGE AMOUNTS OF ELECTRICITY" and the implied amount of danger. I'm pretty sure that there was more danger of getting my ID sucked into the shop vac and strangling me. I'll try switching the modules in the next couple weeks.



I told you early on in this discussion that you won't be all that impressed when you see it done. Done safely and properly, it's not a big deal but done casually without knowing what you are doing... and let's be honest when we started this thread you didn't know what a dimmer rack was... it's VERY dangerous. Now that you guys know what you are doing swap modules. if the problem follows the module. Lock out, tag out and take the bad module to the nearest theater dealer for repair.


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## Synchronize (Mar 21, 2008)

TimMiller said:


> have fun. You may have a bad fader on your console also.



We considered that too, so we tried it on the wall controler. Same thing, it only backed down to about 40%.


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## Synchronize (Mar 21, 2008)

gafftaper said:


> Lock out, tag out and take the bad module to the nearest theater dealer for repair.



That would be very hard to do considering that it is an auditeria and the cafe (or house) lights are controled by that dimmer rack as well. If we lock out then the cafateria will have no lights, and I'm quite sure that the administration won't be too fond of that. Is it safe enough to remove the module then turn the power back on with a missing module, lock the dimmer rack, then lock the booth?


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## icewolf08 (Mar 21, 2008)

Synchronize said:


> That would be very hard to do considering that it is an auditeria and the cafe (or house) lights are controled by that dimmer rack as well. If we lock out then the cafateria will have no lights, and I'm quite sure that the administration won't be too fond of that. Is it safe enough to remove the module then turn the power back on with a missing module, lock the dimmer rack, then lock the booth?


Actually, it is not a good idea to run a rack with a module out. No because of electrical hazard as much as the fact that the large opening in the rack will suck in lots of dust and debris. However, I would not worry about that until you isolate the problem. First swap modules. Then report back to us. No matter what you determine the issue is, you will need to get in touch with your local dealer to get things fixed or replaced. They will be able to tell you how to deal with the problem, and they will probably even come out and help.


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## gafftaper (Mar 21, 2008)

Seems like we determined the "local dealer" is over an hour away. So a "housecall" would be very expensive. It's probably better for you to take the dimmer to them... but first let's prove that it actually is the dimmer that is the problem by doing a swap. On the other hand it might just be a good idea to pay for the house call to have them take a look at the whole system. Given the years of neglect it's had. Make sure when you do the swap you have a working light on the dimmer channel that the questionable dimmer will be in control of.


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## David Ashton (Mar 21, 2008)

Could I suggest that a wise investment for your next budget is to buy a spare dimmer module, this will save you from this problem next time and it will also save money long term, as you can just send off faulty dimmers for repair.
When you know how to do jobs like this it is easy, like most jobs, but we had to be cautious in advising what to do as electrocuting students causes very bad public relations issues.


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## Synchronize (Mar 21, 2008)

Well guys, I know how much you all think it needs to be repaired by a pro, but all repairs are prabably going to have to be made by me, the sound tech, and the building manager due to limited budget ("limited budget" = $0.00). Like I stated (mabey in another thread) a lot of new things that we get are bought by me and the sound tech. So if it needs to be repaired I will probably be the one funding it.

I'm guessing that the fault (again if there is, I haven't tested it yet but I want to get everything figured out so that I can just go ahead with the repair if it proves to be the module) doesn't lie in the breaker itself because breakers are pretty simple and I really don't know of anything that can go wrong with them that could cause this particular problem. But there are recanguar black boxes in the module; one for each breaker. Im guessing that if the problem lies within the module it lies in that. Do you think it would be possible for me to get a new one from the manufacturer? Or is it a generic part that can be ordered from a different company?


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## Les (Mar 21, 2008)

I believe that is the SSR. You will need the correct one, but judging by other posts a 6 year old could do it. No offense to 6 year olds..


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## derekleffew (Mar 21, 2008)

Synchronize said:


> ...But there are rectangular black boxes in the module; one for each breaker. I'm guessing that if the problem lies within the module it lies in that. Do you think it would be possible for me to get a new one from the manufacturer? Or is it a generic part that can be ordered from a different company?


Yes you could get a new one from the manufacturer; you can also probably buy the exact same part less expensively from another source. The most common brand is Crydom (Aromat is another), and the generic name is "PowerCube" or SSR (solid state relay).

See this thread.

I suspect you'll find the problem stays with the slot, and not the module, and thus indicates a control issue. When SSRs fail, they generally either won't turn on at all, or stay on forever. If it IS the SSR, they're around $35.00, unless purchased from the dimmer manufacturer (significantly more).


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## Les (Mar 21, 2008)

I'm going to add to my last post and say that it's probably not the SSR. From what I have read recently, SSR's usually fail pretty quickly and in either full on or full off. Also, you would probably notice a physical deformity when comparing it to other modules, such as melting or a bulge in the plastic from overheating. 

I don't think circuit breakers can fail this way. If so you would have an arcing event which would probably lead to rapid failure in a rather catastrophic manner. 

As others have said, swapping modules to see if the problem follows the module or not will tell you alot. I am personally beginning to think that it is a problem in the signal line or a possible failure or glitch in the control module. That would need to be assessed by someone who is well versed in electronics and diagnostics/DMX. 

Working on the dimmer beyond replacing SSR's would also require solid knowledge in dimming equipment. They deal with much more power than most electronic equipment found in schools and can do an untold amount of damage if done incorrectly. It's a good idea to keep in mind that lives are depending on that dimmer pack not catching on fire after it's worked on. I'm not saying that because I don't have faith in you or your building manager's electronics repair skills, it's more of an insurance/assurance thing.

One final word, don't feel obligated to foot the bill out of your own personal finances.


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## icewolf08 (Mar 21, 2008)

Synchronize said:


> Well guys, I know how much you all think it needs to be repaired by a pro, but all repairs are prabably going to have to be made by me, the sound tech, and the building manager due to limited budget ("limited budget" = $0.00). Like I stated (mabey in another thread) a lot of new things that we get are bought by me and the sound tech. So if it needs to be repaired I will probably be the one funding it.




Lester said:


> One final word, don't feel obligated to foot the bill out of your own personal finances.


I have to echo what Lester said, and I think add a little more force. I know that you love what you do, and working as crew at your school, but you should *NEVER* invest your own money fixing the schools problems. The same goes for using your own personal gear for school functions. Yes, it sucks to have 0 budget, and it sucks to have gear that doesn't work, but it is NOT YOUR JOB nor your obligation to fix it from personal funds. If the theatre department wants to solicit donations from parents to get things fixed, that is one thing, but you set a very bad precedent if you fix/buy gear out of your own pocket, or if you allow personal equipment to be used by the school.

Why is it a bad thing? The school, the district, and the city should be taking care of the investments they make. If you go around fixing things out of your pocket, then the powers that be will never see the need to budget for proper maintenance, because things just magically work. It may seem like a lousy situation, but ask any of the CB members who are involved in academic theatre, and they will tell you the same thing.

If the school administration won't come up with the money to get the equipment fixed then you should get other people involved. By that I mean that you should talk to your parents and the parents of other theatre kids, have them complain that the theatre is not being properly maintained. Go to the superintendent if you have to. Just don't spend your own money.

If worst comes to worst and you can't get the money to get it fixed, don't use the bad dimmer. When someone from the administration asks why there isn't enough light, tell them it is because you need money to get the system fixed. You would be amazed how quickly things get done when the people with the money experience the issue firsthand.

I'll step off the soapbox now, I think we talked about this in another thread too. Just something to keep in mind.


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## Charc (Mar 22, 2008)

I'd have to agree with Alex's last post. However, it's not like I haven't spent my own money, or used my own gear for school stuff.

I personally make a distinction on some of those aspects though:

Tools. It's easier for me to know I have my own tools, the right ones for the job, and easily at hand. I keep these tools in a locked bag, and in a locked room overnight, but they do live at school. People know that these are my tools, and I don't tend to lend them out, and if I do it's to people I know well and trust to respect my gear. So this is something for personal use (plus I love tools and stuff: I'm a geirdo.) Lastly, it's not like I'm leaving my tools behind. If I have work to do somewhere else, or eventually leave school, my tools come with me.

Certain organizations around campus are student driven. Things like coffee house and other events. In these situations I'm either personally invested in the project, or helping out a friend. I don't spend any money on anything for the Theatre Dept, unless I justify it to myself (For instance I pilfered 6-8 cuts of gel, and replaced it with a new sheet of R60).

I think fixing things and investing time isn't an issue, it's where money comes into play. Personally, I find it calming to go into the theatre, even during high-stress / multiple test times, and work on something. So in that respect stuff gets "magically" fixed.

You are also the one without a working lightboard, right? And you do have school assemblies in your building, right? Perfect! Don't worry about a work-around for your next assembly. When the Head Master takes the stage and has to spend 45 minutes talking in darkness, he'll feel pretty stupid, and you'll get something new pretty quick.


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## gafftaper (Mar 22, 2008)

Although I'm sure I'm skilled enough to replace an SSR/SCR, I have never done it. Why? Because I don't want the personal responsibility for what could happen if I did it wrong. When I've had them repaired in the past it's cost about $75. The extra money out of my budget is worth passing the responsibility on to a professional. 

The school/district must have an electrician. If so order the part and instructions and have the electrician do the work. 

As for if it is the SSR or not. Since cleaning out the rack didn't work, I'm voting with Derek that I bet you'll find the dimmer is not the problem. As has been said these things usually break and stay on or stay off. Ghosting is usually more of a control issue. My guess is a problem in either the dimmer control settings or in the console. But don't fear, we are working our way through the list of possible problems here one at a time and cleaning the rack and elimination a bad SSR are the best places to start.


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## porkchop (Mar 22, 2008)

charc I think you were a little hit or miss especially in reference to tools and stuff. Being that I work for Alex I feel pretty certain that I can say he's not telling you to survive solely on the tools supplied to you. I can say that cause every single electrician that works for him brings personal tools. This is an ease of work thing. PTC supplies everything I need to do my work, I prefer the ease of my own tools so I use them. The time when this becomes problematic is when the company willingly or not takes advantage of the situation. Say something like the table saw goes down and so I bring in mine (I wish I had one) so that we can get the job done. I wouldn't even do this, I'd make the company figure out a situation, but you could argue that is being loyal and I might by that. When it's definitely a problem is if the company put off fixing the table saw because they had one that worked. You can imagine the situation pretty easily, if someone in the front office sees a request for money for a new table saw (or to fix the old one) and they walk back there and there's one that works they will put it off or deny the request.
I guess to sum up the difference I'd rely on the "if it ain't broke don't fix it" cliche. If it's broke, it needs fixed, that's the company's responsibility. If it ain't broke but you can make it work better (better tools, more tools) then you might consider personal investment.


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## gafftaper (Mar 22, 2008)

Ok, So I'm dying to find out who called Sync's building manager. I offered to do it but didn't get the message in time to call. When I apologized for not calling he said Well somebody called and explained the whole process. I've sent a pm to everyone who was active in the first part of the thread (Derek, Charc, Alex, Phil, Porkchop... I'm assuming David didn't make a call all the way from Oz) and none of them made the call. So that leaves Soundlight, JD, Steve Terry, Lester, and Tim Miller who either only posted once or didn't post until after the cleaning. Or did we have a lurker from out of the blue call? DVSDave? 

I just wanted to say thanks for calling to whomever did.


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## TimMiller (Mar 24, 2008)

I did not call. I did send him a PM with my personal cell number and said if they have any problem or feel as if they got in over their head to give me a call. So.... Have they gotten it fixed yet?


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## porkchop (Mar 24, 2008)

So i was stumbling the internet and found this, it's kinda a crappy image but it gives a good idea of what it takes for power to hurt you.


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## TimMiller (Mar 25, 2008)

If you have ever taken electronics classes you will learn that 50ma is hardly any power. 1000mA = 1A. So in a 20A circuit means that it will take around 20000mA before the circuit shuts off. Also to most dimmer systems you have anywhere from 400A to 1200A of three phase feeding the panel, in which means you have 3 separate legs of power each being between 400-1200A. Something you dont want to get across. Also be aware contrary to popular belief circuit breakers do not limit the amout of amperage that comes across them, they just shut off after their rated amperage is exceeded. So you can easily have 1200+ Amps traveling down the line. This also means your home! Even though your house has any where from a 125-200A main breaker that big transformer out on the pole or sitting on the ground is stepping down around 60-250+KVA 250-1040A. And the electric lines that run to that transformer is around 60-120KV (yes kilovolts) = 60000V-120000V. 

Here is some really educational and interesting videos of electricity.
This first demonstation video, they are running this setup off of a regular 120/240V generator.
http://www.youtube.com/watch?v=2_4gsPe7BuM

http://www.youtube.com/watch?v=MAlyEMQxTN0


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## porkchop (Mar 25, 2008)

That was my point, very little power (in comparison to whats there) = big ouch


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## Synchronize (Mar 31, 2008)

So I got back to school today. I just switched the modules around and the problem does infact reside in the module. The Building Manager is going to have an electrician come in and look at it but is there anything else that I can do or try to fix the problem sooner?


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## Charc (Mar 31, 2008)

Synchronize said:


> So I got back to school today. I just switched the modules around and the problem does infact reside in the module. The Building Manager is going to have an electrician come in and look at it but is there anything else that I can do or try to fix the problem sooner?



The answer is: yes.

I'd suggest talking to Derek, Gaff, Icewolf, Porkchop, or TimMiller though.

However, if an electrician is coming in, it doesn't really matter until then.


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## JD (Mar 31, 2008)

TimMiller said:


> Also be aware contrary to popular belief circuit breakers do not limit the amout of amperage that comes across them, they just shut off after their rated amperage is exceeded.



Yes, a very good point. Most breakers have a max flash rating of 10,000 amps, and that is why! When you short even a 20 amp line, you briefly have the full output of the pole transformer flowing through your circuit with the only limiting factor being the resistance of the wire. If your are at the end of a long cable, it may not seam like a big deal, but that's because your cable briefly turned into a resistance heater limiting the power flow. We see bigger booms the closer we get to the mains because the thicker gauges have a lower resistance. In any case, there is no limiting done by the breaker, it only switches open after it's response time elapses. By the way, that response time can be all over the place! Some 20 amp breakers will pass a 25 amp flow for 20 minutes before they trip. The higher the current over the rating, the faster the breaker will trip...... Unless it jams! Although rare, it does happen and that can get ugly!


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## derekleffew (Apr 1, 2008)

Synchronize said:


> ... but is there anything else that I can do or try to fix the problem sooner?


Actually, the answer is NO, except to put the module in a place where dimmer#1 on the module (which used to be 5, correct?) is in the least important place, a normally unused circuit perhaps? Then when the electrician comes, show him this thread, and explain what you've done, and suggest politely the replacement of the SSR. In the meantime, you could look at the SSR to see if there's a brand and model# on it so you can get an estimate of the price via the Internet. Like I said previously, these run $30-$50 generally. If replacing the SSR does not solve the problem, I'm afraid you'll have no choice but to contact Lehigh to see what they recommend.


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## gafftaper (Apr 1, 2008)

Yeah I would call Lehigh and describe your problem and ask them if they think it's a bad SSR and ask them for the part number and the name of your local Lehigh dealer... this of course assumes you figured out what model dimmer rack you have. Maybe you can even find a manual for your rack on their website or through them directly.


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## Charc (Apr 1, 2008)

derekleffew said:


> Actually, the answer is NO, except to put the module in a place where dimmer#1 on the module (which used to be 5, correct?) is in the least important place, a normally unused circuit perhaps? Then when the electrician comes, show him this thread, and explain what you've done, and suggest politely the replacement of the SSR. In the meantime, you could look at the SSR to see if there's a brand and model# on it so you can get an estimate of the price via the Internet. Like I said previously, these run $30-$50 generally. If replacing the SSR does not solve the problem, I'm afraid you'll have no choice but to contact Lehigh to see what they recommend.



Derek, yo say "no", then offer that advice? Ahem? 

I'd say look at the module, don't touch, as we want to make sure the electrician sees it its as is condition, see if there is an obvious cause of failure: Completely charred? Disconnected/frayed/burned wire? Or, no visible sign of failure? Then it looks to be the SSR pack. Getting a price estimate and a model number could very much expedite the process.

When is he coming in again?


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## gafftaper (Apr 1, 2008)

My feeling is leave the module alone (other than moving the module to a place in the rack that it isn't on a circuit that is in use). The less you go poking around in there the better. We are pretty sure it's a bad SSR. Call Lehigh and get the information about the part number and get your price quotes.


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## Synchronize (Apr 1, 2008)

There is no visable damage to any part of the module. The electrician should be coming in Thursday. If I understood correctly he does know lighting systems so it shouldn't be too hard for him to figure out the problem and find a solution.


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## Charc (Apr 1, 2008)

Synchronize said:


> There is no visable damage to any part of the module. The electrician should be coming in Thursday. If I understood correctly he does know lighting systems so it shouldn't be too hard for him to figure out the problem and find a solution.



As others mentioned, it is highly likely that the issue is a failed SSR pack. Do the recommend research, and politely suggest it to him.


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## TimMiller (Apr 1, 2008)

Also be sure to check the pins (or make sure the electrican does) on the back of the module, they do sometimes get cooked and cause problems. I have also had trouble with the connector that connects into the control side of the ssr go bad and cause all sorts of weird problems excatly like you are describing. Also if the power pins are charred then both sides (the module and dimmer) connectors need to be replaced.


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## cutlunch (Apr 1, 2008)

It may not be the SSR but the control circiutry that controls it. 
There are the main control boards that do the DMX decoding but each module normally has a small of amount of cicuitry that actualy fires the TRIAC , SCR.

I don't know about this particular dimmer but I note on the Lehigh website I note another of their dimmers use TRIAC's not SCR's.

While trolling the web for info on this problem I was reminded of a problem I had on a single phase 4 channel kitset dimmer. This was a TRIAC setup. The channel had locked partially on but it wasn't the TRIAC but the optocoupler driving the gate. This was only a $1 part without testing the TRIAC would have been replaced without things getting any better.

Also Derek has mentioned buying replacement SSR's etc over the internet from non-original equipment manufacturer. Only do this if you know exactly what you are doing. Some parts may have only one charcter difference in their part number but the part is totally different or has different ratings. Also the person who sends you the part may not know the difference either.

As an exercise checkout the following link and try and workout which is the most robust TRIAC in the
BTB08-600 family.

http://www.onsemi.com/PowerSolutions/parametrics.do?id=826

There was an example recently of a parts store stocking what they thought was an insulated TRIAC but they had been supplied with the non-insulated version. If you don't know how dangerous that was then you shouldn't be messing around modules at a component level.

So unless you are skilled I would suggest always sending the module board to a licenced repair agent. This is also because they will have test jigs to run the module on safety with power flowing through it. This means they can take live voltage readings and not just guess what the problem is.

And I am not aiming this just at students, I know a lot of adults I would never let work on a dimmer pack.


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## TimMiller (Apr 1, 2008)

cutlunch said:


> There was an example recently of a parts store stocking what they thought was an insulated TRIAC but they had been supplied with the non-insulated version.



This happened to me recently. It was designed to switch a 250V cap on and off and there were two of them. Seeing two legs of 250 go to ground on a single piece of metal aint pretty. Made a bright purple light. Blew a hole through the piece of aluminum they were mounted on.


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## JD (Apr 3, 2008)

cutlunch said:


> As an exercise checkout the following link and try and workout which is the most robust TRIAC in the
> BTB08-600 family.



On triac numbers of the BT family:

BTA16 600B (for example)

BTB Non-insulated
BTA insulated

16 16 amp triac (not always the exact amperage, see below)

600 means that it has a breakdown voltage of 600 volts.

Also important is the case style. Three cases are used on the BT's. This can be tricky, here is an example of the 25 amp series:

BTA24 TO220A case (small tab like the four channel packs use)
BTA25 RD91 case (Round metal flange)
BTA26 TOP3 case (Larger flat plastic case)

I can think of no reason to use the non-insulated version, they are just trouble waiting to happen! The reason they are made is legacy. (They were around longer and some old equipment makes use of the flange. None in the lighting industry that I know of.)

EDIT: Oh, almost all dimmers use 50ma gate. (All that I know of) Snubber settings are not a factor unless you have a prehistoric dimmer that uses a pulse transformer as compared to an optocuppler. (Haven't seen any since the 70's)


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## cutlunch (Apr 3, 2008)

JD you went into more detail then I was expecting. 

But this shows how carefully you have to read the datasheets.

The thing I was looking for on the particular part number I gave was the Di/Dt ratings are higher for one then another. 

Also Ig is at 35mA for one and 50mA for the other. Put one that requires more Ig current then the control circuitry supplies and you get faulty operation.

Snubber circuits don't just apply to pulse transformer circuits. They are there to stop the current flow through the TRIAC's at the end of each AC half wave cycle so the current is cut off cleanly. Especially important when you are driving loads that may have some inductance eg transformer's etc. SCR's and TRIAC's turn on allowing current to flow through them when they receive a control pulse on the Gate pin. 

But to turn them off the current going through them has to fall below a certain level else they won't cutoff. This normally happens at the end of each AC half cycle. An inductive load can generate back emf which causes enough current to flow back through the device to hold it on until the next proper firing pulse is received and it is turned on fully again. So that is why we use snubbers.

TRIAC's and SCR's have whole sections to themselves in tertiary electronic courses. So you can see why I say make sure you understand the parts before buying generic ones from a non-original supplier.


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## JD (Apr 3, 2008)

Yea, an inductive load will have a flow pattern that looks more like a square wave. Although it must pass through zero, the time spent doing that is much smaller meaning an inductive turn off requires tighter V/us / A/us Di/Dt number to insure the device is off. Most dimmers also contain an external snubber in the form of an R/C network across the device as well to protect against both this effect and "flyback generation."

As far as Igt drive, I can't believe how universal that has become! My old (30 years) EDI packs use the same photo-coupler as the latest D4DL20 pack I serviced yesterday! All greatly exceed an Igt of 50ma. HOWEVER, you are correct in emphasizing the point that only a person with the proper training and experience should actually attempt service, or even parts id! In another recent thread I pointed out how even design engineers sometimes get circumvented by production "bean counters" to the detriment of the customer (16a triac on a 10 amp dimmer!) The aforementioned EDI packs used 130amp SCR bridges for a 2.4k 20 amp load, which is more in lines with what we learned as engineering students, to use a safety factor of 5 on solid state power devices.

EDIT: Which brings up "Frankendimmer" ! (My thoughts about resurrecting about 96k of old analog EDI I have, by ripping out everything up to the photocuppler, and replacing it digital!) (Please do not try that one at home!)


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## TimMiller (Apr 4, 2008)

Thing i like about analog is if the board up and quits at least you can make channels come on by wiring them up to a 9V battery. I have had to do it before in a pinch, but the show must go on...


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## JD (Apr 4, 2008)

Yea, never had to worry about those old systems taking a dump in the middle of a show. On the other hand, those old 100 pin snake connectors were never quite roadie proof! 

<tangent>
Here's a tip that 25 years too late! I always found that those 50 pin phone connectors to be the most reliable! (and dirt cheap too)
</tangent>


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## TimMiller (Apr 4, 2008)

yep, i used to have a bunch of those laying around. I have now pretty much gotten all that stuff installed back into phone systems.


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