FWIW, it may still be the AC Regulator. I received a bunch of "new" AC Regulators before they were declared obsolete, and they would start out with proper smoke and pretty quickly tail off to no smoke. When I checked, there was still a little voltage coming out of them, but not nearly enough to generate smoke.
I went through my whole stash of AC Regulators with no success. The bummer is early Legacy can't be skywired to run the smoke from the R4LC like TMCC can, so if the AC Regulator doesn't work, you're out of luck!
I finally put a large bandaid on the problem. The only way I could get smoke that was command controlled was to use the anemic output of the broken smoke regulator and augment it with a separate driver board.
