Control/Dimming "Singing" LMI L86 Dimmer Pack?

[marlonhurt]

I have an old L86 dimmer pack that is "singing"--it makes a two-toned, three-second long whirring noise every twenty seconds or so. I keep it pretty well maintained, so I don't think it's a fan issue. It sounds like it's singing along to a power cycle or something. Just wondering if anyone else has encountered this with these older dimmers and whether there's a way to stop it. (It can be quite maddening, lately, working in the dimmer room.) Thanks!

 

[starksk]

re: "Singing" LMI L86 Dimmer Pack?

I can't say that I have ever heard an L86 Rack "sing". Perhaps DavidNorth or STEVETERRY could shed some thoughts as to which components could be producing that noise.

In the meantime, can you localize it to a specific area within the rack?

We (ETC) can still repair L86 modules and racks so when we do narrow it down, we can get the appropriate parts in for repair.

Also, please feel free to give us a call at 800-688-4116 if you would like to do some additional troubleshooting via phone.

 

[JD]

re: "Singing" LMI L86 Dimmer Pack?

Outside of fan bearings, about the only thing that sings in dimmers are the chokes. On an older dimmer, the MFP coating may have dried out and the windings buzz a bit. I have heard an occasional circuit breaker sing as well. Really a matter of tracing down the location to see if it is a single module or something in the frame.

There are a number of cheap ways to re-goo the chokes if they are singing, but as this involves opening things up, the usual "Qualified Servicer" disclaimer applies.

 

[derekleffew]

I have an old L86 dimmer pack that is "singing"--it makes a two-toned, three-second long whirring noise every twenty seconds or so. I keep it pretty well maintained, so I don't think it's a fan issue. It sounds like it's singing along to a power cycle or something. ...

Is the noise dependent on the level of the dimmers? Does it vary at all? Is it still present when all dimmers are off/at 0%?

 

[marlonhurt]

re: "Singing" LMI L86 Dimmer Pack?

Hi Derekleffew, the sounds happens independent of what levels the dimmers are set at, though it does stop when I cut power to the pack. It does not vary though; if I could scrape up a pitch pipe I could probably find the two notes it plays over and over...

JD, any preferred adhesives if it does turn out to be loose chokes?

Thanks all! This is the weirdest issue I've faced in my time so far!

 

[DavidNorth]

re: "Singing" LMI L86 Dimmer Pack?

If this is a portable pack, then the fan is wired directly to the A phase input. So if it sings immediately upon power application and stops just after power removal, my bet would be on the fan.

You can remove the grill from the front of the pack [6 screws], clean out the filter and blow out the 20-some years of dust and grime from the fan to see it that takes care of it. Likely it won't as it will probably be a bearing going bad. Yes, we do have this part.

If you are careful, you may wish to power up the pack with the grill and filter still out and see if you can correlate the two pitches with perhaps two speeds of the fan. Might want to make a white mark on one fan blade [when power is off!] so you can more easily see if the fan is speeding up and slowing down. Hopefully it will be obvious that the fan is the issue and you want have to mark the blade and look for changing speeds [which may not be happening].

Let us know what you find.

David

 

[JD]

Re: "Singing" L86 LMI Dimmer Pack?

I used the Miller Stevens stuff:
Coatings

Almost any of them will do, but I would recommend the Silicone version as it is both high temp and high Dielectric strength.

Then there is always the cheap way out, like GE silicone, but if your are going to do a bunch of them, I'd order in the MS stuff.

PS: sometimes if you contact them, they will send out free samples.