Circuit mostly traced out, no apparent damage in the high-voltage section apart from the electrolytics and a cracked capacitor in the snubber network. The power FET's are all OK (tested up to an amp or so DC drain current at about 1V VDS) as is the flyback diode. I found a 215 ohm 1/3W resistor in the input suppression circuit, which was apparently undamaged but reading open circuit. I wonder if it was ever correct? It's possible there is another problem in the control circuit, FET drivers or the isolated side, but the symptoms point to a primary side problem. I've ordered replacement electrolytic (Kemet 470uF/200V) and a replacement WIMA FKP-1 for the snubber, even though the original was still reading 913pF - this is outside the tolerance band, so it may have suffered a partial internal failure. However it's odd that bad electrolytics could give a total failure to start, unless the bootstrap supply was not coming up properly. I hope not, as that seems to use a mysterious unmarked VDR(?) which reads about 1kohm at low voltage, switched straight across the rectified mains by a power FET.