TI UCC2985 phase-shifting PWM controller driving 4 x F740 500V 20A HexFETs in a full-bridge, running at 340vDC supply, driving the output transformer, the output being rectified by two BYT16P dual fast 20A rectifiers. Feedback from output to PWM is via a pair of opto-isolators. There are a pair of FA3624 PWM controllers on a daughter board each driving an FP460L hexfet as a single ended flyback converter to provide logic voltages
Crikey! I'll just be happy if I manage not to set fire to it when I plug it in!!
Thanks for the investigations Irving - i've got a couple more weeks of fiddling with leadscrew and alignment then I think I'll suck it and see what happens at 42V. (unless your reverse engineering gets finished before my machine)(possible)

PS. cheers for the ebay spades link Hank - i'm nowhere near Maplin :(