Control/Dimming SSR Failure, Lee Colortran dimmers. Who done it?

Goph704

Active Member
The story:
please note this second hand. During a Recent focus at one of the older buildings, a light froze in the on position. This particular circuit had been functioning well, up to this point, and even tested out normal three weeks prior. The head electrician eliminated all variables in the board, and after a time between 15 minuets less than half an hour decided to check the dimmer racks. He came in and found that the circuit in question was producing an incredible amount of heat. he flipped the breaker off and contacted the House T.D. who pulled the card. The TD found that the SSR was cooked. The center of the SSR was burnt out, while there was no scorching anywhere else on the SSR. The TD then replaced the dimmer unit with another one from our "good" pile of units. When he flipped the breaker back on the new unit started to heat up in the same way as the old one. The Dimmer unit was pulled and the light was re-circuited. That's the story.

the investigation:
I came in the next day, and immediately looked at the rack. Nothing was obviously loose or shorted where the unit tied in. I looked back to the raceway, The circuit had been replaced recently but it tested out fine. I put in a new unit and tested the circuit. It was not functional. The cable had disappeared, but the instrument was working well with no shorts. I performed a quick autopsy on the "cooked" card and found that The trigger on the circuit in question had indeed blown open since I could get continuity between points A1 and A2 which I should not have been able to get without trigger voltage. I then tested the breakers and found that they were in working order. I removed the SSR and found that the heat sink was very weak, but present. I replaced the old SSR. We found a spare DMX card from downstairs and replaced it and found that while the circuit in question was working other ones were not, so we put back the original DMX card. I marked the spare as bad. When I replaced the original DMX card, suddenly the circuit was functional again. The Circuit is now off, and I Have never seen it produce any heat.



Conclusions or Questions?
So, this is my first month in this space and I'm still working out a lot of the Bugs. I know for a that the SCR was blown open and most likely cooked while the PE hunted through the board. I'm willing to believe that a short in the cable caused the SSR to blow open in the first place even though I can't prove it. I have not eliminated The failure of the Choke even though I have no good way to test it. I'm also willing to believe that we have more bad cards than I thought we did. The two things that I'm the most concerned about 1. The heat from the second unit that the TD reported, and 2. That I might be missing something else I haven't thought of. Any thoughts Ideas or suggestions? Is there a more sinister culprit possibly lurking in the wings, or is this just an Isolated incident caused by old dimmers?
 

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How old is the unit? Sometimes when a SSR fails it will develop internal resistance as compared to being a dead short. A good SSR will throw about one to two watts of heat for every amp running through the circuit. In other words, a 20 amp load will throw about 18 to 36 watts of heat. A bad SSR may throw much more in a state of failure.

The second question is, are you sure it is an SSR? I say that because there were a lot of dimmers built in the 80s that used back-to-back potted SCR modules. (Early EDI Scrimmeretts come to mind.) On these, the opto-isolators are not part of the module, so they will not give you the readings you would expect. Many multi-meters use a 1.5 volt battery so they may read a stacked junction as "open" due to the fact that the meter voltage is not sufficient to overcome the junction drop.

Bottom line, the heat by itself would not necessarily mean the circuit was being overloaded, and multiple modules may have the same problem if they are the same age.

Very rare for a choke to fail. A good one will usually read as a dead short on a multi-meter. The only chokes I can remember replacing are ones that were cooked and lost their insulation. (They still metered good.)
 
The rack itself is 22 years old. However apparently five years ago an Update on the system happened when they changed over from CMX(?) to DMX, and regular repairs have happened on the rack for it's entire life time. I'm not sure if these are the back to back SCR's your thinking of. They are manufactured by Crydom if that helps. I'm really concerned about the possibility of a large system failure, so what is the possibility I'll see more cooked units like the one above?
 
The rack itself is 22 years old. However apparently five years ago an Update on the system happened when they changed over from CMX(?) to DMX, and regular repairs have happened on the rack for it's entire life time. I'm not sure if these are the back to back SCR's your thinking of. They are manufactured by Crydom if that helps. I'm really concerned about the possibility of a large system failure, so what is the possibility I'll see more cooked units like the one above?

Don't know how many dimmers are there, but chances are there are several circuits that have seen heavy load over the years, and many that have seen little or no load. SSRs, Triacs, SCRs, they all age based on loading so it really is anybody's guess. What happens inside is that the junction heats and cools an over the years develops microscopic cracks in the silicon substrate, as well as cracks in the bonding and the welds where the leads attach to the junction. Eventually, there is enough damage that a cascade failure occurs in the whole junction. A "new" SSR may sit on a shelf at a parts dealer for 20 years and be just as good as a newly manufactured one of the same type.

If you see visual heat damage on certain modules, then those are most likely to be the ones to fail, and I would load them lightly. Let me qualify that statement as I am not recommending you take things apart unless you are qualified to do so.

As far as a massive system failure, that is more likely to happen due to a firing card failure as compared to a dimmer module. Most likely, the type of failures you will see are going to be the occasional loss of a module much like you already saw. SSR failures usually manifest themselves as dead or on all the time. In some cases, you will have flicker problems. All three can be localized by swapping modules.
 
I have not been around older dimmers much, but I would call up Leviton to do a inspection of the rack.
Also you had a "?" next to CMX, CMX was ColorTran (Lee/Leviton) 's own version of DMX. Some of their consoles still have a CMX output option.

We have an i series rack from Colortran, and some of our circuits get stuck on randomly and the only thing to do would be to reset the rack.
Besides that we have only had one module mysteriusly fail.
 
I have not been around older dimmers much, but I would call up Leviton to do a inspection of the rack. ...
Leviton/Colortran will be next to useless when dealing with a 22 year-old Dimension 192 dimmer rack.
...I'm really concerned about the possibility of a large system failure, so what is the possibility I'll see more cooked units like the one above?
As JD said, I wouldn't worry too much about a catastrophic system failure. Just keep some spare SSR s on hand. If a problem develops in a control card, Steve Short of Lite-Trol (and others listed at Service and Repair Vendors - ControlBooth ) can easily repair them.
 
Just throwing this out there, cheapest place I have found replacement power cubes of the 2.4k dual module type is at Production Advantage. They sell them cheaper then even the electronics part companies. I just swapped out 6 in my 20+ year old dimmer racks.
 
Even though you haven't said it yet [that I saw], I am assuming this is a D192 rack. Is that correct?

You did mention that you replaced the DMX card. Would that be the D192 control card at the bottom of the rack? There would be three of them - one for each phase.

Before you replaced the DMX card, did you notice if other dimmers in that column were working?

It certainly looks like you had a fairly catastrophic power cube failure. This can be from a number of reasons, some of which were mentioned above. Dead short in a cable or fixture, dead short in a multicable feeding a strip, dead short in a plug in a strip [broken and flopping loose does this], lack of heatsink compound or old dried out compound combined with heat and age, or a bad run of power cubes.

Interestingly, there was a bad run of cubes back in the late 90 and early 91 and this might be one of them. There should be a 4 digit code on the side of the cube which will tell me if it one of those. Of course this is uncommon these days and would be made by Douglas-Randall.

The reason I asked about other dimmers in the column before you changed out the card is that I am trying to figure out how bad your DMX card is and whether the cube took out a lot of stuff. If the high voltage side shorted over to low voltage then you might have also lost more dimmers in the same phase due to combined control circuit common or +5 [don't remember which on these racks].

I have seen cubes fail like this and emit large amounts of smoke and/or catch fire. It is rare, it is a little disconcerting, and it usually does more damage. Certainly age and abuse are prime contributors. If you have failing fixture wires, damaged raceways and connectors, poorly maintained jumper cables, clogged fan filters, or non-working fans, older dimming systems are surely suspect to this and will fail in exciting ways. Older lighting inventory and rack maintenance is a must.

Be glad to help. Let us know the answers to the above.

David
 

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