Sensor Dimmer Rack Air-Flow Problems

[theILLUMINATEDfrog]

I encountered an issue that I had never seen before this weekend.

While programming for a show around midnight Friday, my theatrical fixtures started fluctuating intensity pretty severely. It got to the point that when stepping between programmed cues, some instruments would not turn on at all (all S4 ERSs) and some would only fire at 15-20%. This was 11 hours before my first matinee-- almost time to panic.

I ran down to the racks to see the 1 rack (92 dimmers) flashing red at me with the error message "Air Flow Problems." I killed my board as to stop pulling voltage and did my best to blow-off any dust on the fans/coils, etc (it was fairly clean). The error message continued throughout that night (i went home to give the racks a rest). I reset the rack several times, but the error persisted.

the next morning at 6am I was still receiving the same error. Eventually it went away and the show went on without a hitch.

It seems fine now, but I'm still curious. There were no obstructions, not overly dusty, resetting didn't help, and then it just went away-- so what was it?

My only guess is that after 10pm when our air circulation system turns off, the room which houses the racks gets sucked "dry" by the racks' fans and there is "not enough air" to do the job. This doesnt make too much sense because it's not like the room is a vacuum, there is air, otherwise I would suffocate too. I resorted to this theory based on the timing: Error once the air turned off, Error gone at 7am once air turns back on. Do I always have to keep the door to that room open (large room, not closet - at least 20x20) to increase airflow to the racks?

Any of you Edwin Jones guys have an answer? Anyone else encounter this issue?

 

[millamber]

What iteration of Sensor dimmer rack, the Classic or the Plus?

If it is the classic, (I assume it is because of the "red" beacon light) which software version are you running? There was a bunch of faulty airflow sensors in a particular version of code in the classics. Plus, an airflow error is generally a persistant error, requiring you to clear it out using the clear button on the face of the CEM, so its not really suprising it would stay on through a reset.

You might have a bad sensor, or it may just be dirty. Just behind the fins on the right hand side of the CEM there is this round button like object. That is the airflow sensor. It may or may not have a little gold shield over it, depending on how old the CEM is. Blow that out with some canned air (as always, if you are going to remove the CEM from the rack, Make sure the main Power is off first), clear out the airflow error and see what happens.

Also, make sure the filters in the rack are clean. They live on the backside of the door and are removable. It is the side you don't see when you open the door that is the dirtiest, so pop them out and clean them off with a vacuum.

 

[derekleffew]

See the threads Dimmer Temperature, Dimmer Racks?, and maybe this ETC KnowledgeBase article.

You're exaggerating slightly, and the statements about CEM's having an overheating problem are slightly inaccurate (and I'm picky about such things).

By all means, proper ventilation to a dimmer rack is a very important thing and should be fixed as soon as possible if that's your problem. In reality, though, the overtemp alarm is triggered well before there's any risk of damage to the rack. It's a feature that's specifically designed to prevent such damage from occurring. That's why the rack shuts off all the outputs when it happens: it gives things a chance to cool down.

Some CEM classics (the kind with the number pad on the front) had an issue where the airflow sensor would fail to detect proper airflow consistently. The symptoms were similar: lights flickering or turning off, but the message displayed would be, "airflow errors." There's a little piece of metal that can be added to CEM's that have this problem, or the airflow sensor can be replaced with a different version (though the latter is somewhat dependent on software versions).


Feel free to call ETC even if you don't expect to be able to get anyone to pay for a tech to visit. Their support staff will gladly talk you through some troubleshooting steps that will likely solve your problem. Sending a tech onsite is always the last resort anyway, since it can be quite expensive.

ETC Tech Services: 1-800-688-4116

(Edit: Sorry, posted simultaneously with millamber.)

... I killed my board as to stop pulling voltage and did my best to blow-off any dust on the fans/coils ...

There are several things wrong with this statement. Let's hope you misspoke. The console has little to do with voltage at the dimmer rack. Always LOTO before servicing.

 

[Les]

If not a faulty airflow sensor, it sounds like you just over-temped them, and the AC shutting down at 10pm probably had something to do with it. Nothing to do with a vacuum or anything like that (the room is not air-tight, believe me), just no cool air available. (It is advisable to locate the dimmer racks in a room that is independently air conditioned 24/7).

What was the temperature in the room when you noticed the issues? We always tried to keep our dimmer/amp room at 68 degrees [at least that was the goal].

 

[BillESC]

We have the same racks in a theatre I work in. Twice a year we take out the dimmer modules and blow them with compressed air. Works like a charm.

 

[FMEng]

Les asked the key question here, was the room hot. If the room was still a comfortable temperature, you could have one or more failing dimmer rack fans. When the bearings are starting to go they could be intermittent.

I haven't seen a Sensor rack so I don't know how many fans there are, or whether it would be obvious if they are not turning at full speed. But I know that failing fans are pretty common in the large electronic systems that I work with.