Christian,
I looks like at some point in the past the machine has been phased incorrectly. Now, if the spindle is running the correct direction, that problem is solved. Fanuc SCR drives dislike two things more than anything else:
1) Being run with reversed phasing (They blow fuses or sometimes scr's when phased incorrectly, even for a few seconds).
2) Being run on a phase converter.
I've been following this thread for awhile, but without re reading it all again, I'm not sure if you've mentioned if you have good three phase here or a phase converter.
This is a good control, and these are good drives. Parts are still out there.
Hang in there.
Warren
www.uptimecorp.com