Theatre on Thursday: Diagnosis

For the past few days I have been trying to track down a phantom problem.  It is only phantom in the fact that I can’t reproduce the problem outside of the show.  That, I suppose, makes it definable is an intermittent problem.  This of course, is the most difficult of problems to diagnose and to solve.  Certainly a very frustrating problem.

What is the problem?  Well, I have a moving light that seems to intermittently decide to just quit.  For those of you who are not theatre people,  or don’t work with many moving lights, this particular fixture uses an arc discharge lamp.  That means that the light is created by maintaining an electric arc between two electrodes.  It is very similar to the arc that is used in arc welding except that it is contained inside a lamp.  Here is a photo of the lamp, just so you can see what I am talking about:

This is the HTI 700/D4/75 arc discharge lamp. This particular lamp has 99 hours of burn time on it. You can see the "arc gap" in the center of the globe, this is where the electric arc is created. The arc excites gases in the globe and emits light.

So, a few day ago this problem showed up.  We made it through tech and most of the first week of performances before the problem began.  The fixture drops the arc (douses out) and displays a lamp error message.  So my initial thought was that it was a bad lamp.  While this is rare, it is possible, and the least expensive problem to fix.  In fact, with a lamp this “young” (only 99 hours into it’s 1000hr rated life), if the lamp failed I could make a warranty claim for a new lamp.

Unfortunately the lamp seems to not be the problem.  I installed a brand new lamp and the problem persisted.  Thanks to my friends over at I had lot of other suggestions of things to try.  Some are not really feasible at this point in time, but after the show closes I can try them.  Today I actually got up in a focus chair to string a new circuit for this fixture that takes it off of the dimming system to eliminate any power issues that may have occurred there.

Well, I have been unable to solve the issue, which leads me to believe that the problem lies in the fixture and not the lamp or the power feed.  This probably means a more expensive fix, but I am sure that I can have it fixed.  Though I would certainly take any advice any theatre folk may have!  Such is the nature of life in the theatre.  I just like to look back on my favorite quote about the theatre from the movie Shakespeare in Love:

“…allow me to explain about the theatre business.  The natural condition is one of insurmountable obstacles on the road to imminent disaster!
…Strangely enough, it all turns out well.”






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