I seem to be the "Go to guy" in our community for fixing
dimmer racks. I service two colleges and one
community theatre that all have sensor racks, and two high schools and my own
theatre that have
EDI mark VII racks. Of these several
dimmer racks, I have only had to replace SSRs on one of the
EDI racks and one of the Sensor racks.
The
EDI rack, is from my own
theatre and in every case I can
trace the failure to blown lamps. On the Sensor rack, which is a single rack, and has had about 8 failures in less than a year, I am pretty sure that the
theatre has either one or several cables that have an intermittent short. This
theatre is also the least maintained, and seem to ignore any advise I give them about checking their cables and instruments.
I also have made quite a few repairs of "
shoebox dimmers" for the various facilities. When I replace a
triac in one of the
shoebox dimmers, I always take the new one to a 20 or 24 amp
triac.
All of the failures on the
shoebox dimmers can be traced to blown lamps or more commonly shorted cables. The
shoebox dimmers tend to be used for practicals, where it is not uncommon to use "Zipcord" or Christmas tree lights.
When a lamp blows and part of the
filament or support wires short against each other, the
current draw, although only briefly, is too fast for the
fuse or
breaker, and too high for the solid state device, be that SCRs,
SSR,s or Triacs.
I see the replacement parts as expendables, just like
gel or
gaff tape. It's just part of doing
theatre business.
Tom Johnson