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Electronic Theatre Controls Inc

Test L86 Power Cubes (SCRs/SSRs)

There are a few ways that you can test for faulty used power cubes--they should pass the three tests outlined below. 

Keep the cubes that pass these tests in a special parts container away from new ones, and keep them marked so that you know if there is a problem with it that it was recycled.

  1. Throw away any power cubes that have burn marks, soot marks, or holes in them.
  2. Set a meter for continuity, place one probe on power input to the cube and the other on power output.  Reading should be in the megaohms range.  Any cube that registers close to zero or zero is bad, as it is locked on and will not dim.
  3. Place a fused or breakered 120VAC voltage on power input.  Place a meter set for AC on the output (relative to neutral).  Use a 9vdc battery across the control pins to turn the cube on.  With the 9vdc battery in place, the meter should read 120VAC.  Without the battery, the meter should read 0VAC.  Cubes that don't pass this test should be thrown away.

A couple of things will help you maintain the life of your L86 system and its power cubes:

  1. Dead shorts blow cubes faster that anything else.  Keep your extension cables and fixtures in good repair.  You may blow several dimmers before you realize that hot and ground are shorted together in a frayed end on a stage pin extension.
  2. Keep the fans in working order and keep the filters clean.  Proper cooling is paramount in high-density dimming.  A bad fan should be replaced as soon as possible.  Hitting reset on any EM64, or EM264 in a rack will drive all the fans in that chassis on.  You can remove the filter and see the fans turning.  You may need a flashlight.  While the filter is out, wash it in water and allow it to dry before reinserting.
  3. When you replace power cubes, remove all of the old heatsink compound.  When putting in new cubes, use a liberal amount of the heatsink grease and tighten securely to the tray.  Wipe off the excess so as not to gather dust and dirt.  If you have any dimmers with sil-pads (looks like a white grease covered piece of foil under the cube), remove them, do not reuse them, and use heatsink compound instead.  Any electronics store will have this.
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