Maybe the diode testing method will help you locate where the problem is. See Kerry's post at The ultimate DIY? A Stax SRM-T2! This have helped me a couple of times.
The two 1K gate resistors in place, 240R as source resistors (not 250R – took what I had). No LED and its 175Ks and no A bridge. Is there more to consider. The lower source resistance couldn’t be the problem or…?
Some time ago I did the new KGSShv board with Only IXYS parts. With power on both channels showed -380 V. Same thing both boards. Today I replaced 10n100d with c4686 and then it works.
Have anyone built KGSShv new board with all IXYS parts and have it working?