Control/Dimming Leprecon mx1200 dimmers vibrating/buzzing

[mozsey]

Hello there folks at Control Booth. I have a weird thing happening in a theatre I am currently designing at. I've designed in this space before, and this has never happened. Our Leprecon mx1200 dimmers, which are quite old, are buzzing/vibrating? As in, I was hard patching and when I entered the room, I heard some buzzing. I thought nothing of it, thinking maybe there was something in the walls doing it and I was going to talk to my boss about. But when I was plugging in a cable, I noticed the buzz was actually coming from the dimmers themselves! Seems to be happening with our first bay, 1-12.

My question: Why? Is there some time of warning system inside of it? I can't seem to find much help online, so I decided to come here. Any help would be great!

 

[JD]

If the buzz changes in tone as the dimmer setting is changed, then you may have one or more chokes that have become mechanically loose. This can happen if what holds the choke in place has dried up or shrunk over the years, or if the coating used on the chokes has dried up and is cracking or falling off. Usually, this will not lead to a failure. You may be able to get a servicer to tighten things up, or even inject a material such as MFP or silicon onto the offending chokes.

 

[mozsey]

No change in tone when brought to full. It's weird, I thought it was following a pattern, but now it's random. And I'm not certified, so I'm sure as hell not opening it up to take a look. And we probably won't be able to get someone to take a look at it until after this show I'm designing.

 

[JD]

No change in tone when brought to full. It's weird, I thought it was following a pattern, but now it's random. And I'm not certified, so I'm sure as hell not opening it up to take a look. And we probably won't be able to get someone to take a look at it until after this show I'm designing.

Usually, the buzz is caused by the chokes, but there are some other sources as well, such as a loose core or core plates in a power transformer. I would not open it up due to the inherit dangers. Although I could not possibly be able to diagnose this problem with 100% certainty without actually looking at the unit, chances are this is a magnetically induced vibration and will not be an issue for you. If you have the opportunity to have it professionally looked at, take it. There is always the possibility that the noise is being conducted there from another location, or that a fan has died. Obviously, a fan failure would lead to an overheat condition if the circuits have a good load on them.

 

[mozsey]

I should note this isn't a constant buzz. It'll be BZZZZZZ silence for 10-20 seconds BZZZZZZZZ like a text message that's going unanswered on an iPhone.

 

[JD]

I should note this isn't a constant buzz. It'll be BZZZZZZ silence for 10-20 seconds BZZZZZZZZ like a text message that's going unanswered on an iPhone.

Important distinction. Leans in the direction of a fan motor. When the bearings start to go, they may make noise briefly while the shaft oscillates, only to go quiet for awhile. Unless of course, the last service tech left his phone in the rack

 

[mozsey]

Could be the last service tech. If a phone from the 90s would fit in the rack haha.

 

[mozsey]

Weird. Today I come in, and it's not making the buzzing sound, yet all my lights are functioning properly. Thoughts?

 

[FMEng]

The dying fan decided to behave for a while, which they are known to do. Or it has seized completely, which means the dimmers will either have a greatly reduced lifespan from baked components or it will shut down due to thermal limits being exceeded. Of course, nothing bad will happen until the middle of a show. Get it repaired ASAP, and do maintenance on the others. PNTA should be able to service them.

 

[JD]

Agreed. Get someone to check airflow and make sure that section is breathing. At least give the facility the heads up that there could be some damage being done.

 

[FatherMurphy]

The MX series first came out in the late 90's, so your dimmers are about 15 years old at most.

There are no transformers of any significant size inside, so delaminating plates isn't a worry. I haven't heard of any troubles with the chokes, either. The fans, however, are a common failure, and as noted above, the bearing noise can come and go.

Changing the fans does require opening the case of the 12-pack, so if you aren't comfortable doing that, call in a service tech to do it for you. There are two fans inside, and while the tech is there, they may as well change both of them, along with checking the heat sinks on the dimmer cards for dirt. if you have several packs, you might try to get all the fans changed at once, and maximize the service call.

In the meantime, if one or both fans die, a sensor should shut down the pack until it cools a bit, rather than cook any internals. Since you are only hearing noise at this point, you shouldn't be too far down that path, but I wouldn't let things go much longer before fixing the problem.