Power cubes failing at an increasing rate

...I am surprised that you haven't seen a response to this from ETC yet... There are two major reasons for failures of "power components", whether they be discrete SCRs or power modules: Heat or electrical surges. Heat can be due to loose line or load wire terminations on the module... make sure the connections are tight. Heat issues are also caused if the module is not bolted down tight or has a poor "thermal" connection to the heat sink. It could also be a localized air flow problem. Although Sensor racks have fans and temperature sensing, a rack running with less than a full load could have several isolated "hot" (=too warm) dimmer modules that would not set off the thermal sensors. As for electrical surges, voltage surges can be caused by (d'oh...) lightning or heavy machinery (think large A/C compressors) starting on the the same utility transformer. Current surges can be caused especially when high-wattage lamps fail. The dimmer choke tends to minimize this, but...

My suspicion is heat. I know of 30+ year old systems with the SCRs bolted to huge heat sinks that have the original components. I also have some experience with an older system that had the power modules bolted to the rear panel, which had heat sink-like "fins" on the exterior. It depended on "convection" to cool the rear panel. On that system, the modules in the "middle" of the panel tended to fail more frequently; which I felt was because of greater heat build up in the "middle" of the panel. On the Sensor racks, check the "inlet" fins on the modules. Do you have access to a thermal imaging camera?...