Today I went in to try and diagnose the problem with reduced power. Well, the problem is gone, but I didn’t do anything to fix it.
My hopeful theory was that the surge suppressors inside the high voltage power supply were starting to fail again. That’d be a cheap and easy repair. I opened up the high voltage power supply and found no visible damage to the surge suppressors, and they tested good with a multimeter (now in the toolbox for future use).
The power faded out during a class session, where we were running small jobs with longish pauses in between. It was a warm day, but far from the warmest we’ve had to deal with this year. Today I tried running several longish jobs at high power to stress the system, but couldn’t get it to misbehave.
Terry ran some quarter-inch acrylic cuts last night and also got normal performance (60 speed and 100 power to cut through).
So, I don’t know what was wrong, or whether it will be wrong again anytime soon.