I have an old VMC with a GN/Fanuc 6Mb, circa 1982.
(Yea thats right, in my backyard - I like to tinker).

The 3ph power is being supplied by a new 30hp rotary Converter.

Everything is working great (All 4 axis) except getting
a 401 alarm upon splindle accelleration or decelleration.
It is a 10~15hp servo-driven spindle (More specs avail).

Example:
An M03 S100 Command works OK.
Upping the rpm from there to S200 Works.
In increments of 100rpm things are OK, all the way
up until 900~1100 rpm, where it gives me a 401.

OR if I try to go strait from zero rpm to say, S300,
it will trigger the same 401.

Ingeneral, it seems to trigger the 401 anytime
the spindle motor is accellerated or decellerated
in any brisk (read: 'Usable') fashion.

The controller's 401 diag screen lists all zeros.
There are no alarm lights on the PCBs staying on after the 401.

The only evidence that anything has happened is the
401 alarm screen and that all the Velocity Control boards shut down.

the GN/Fanuc Manual is of little help. It does not really cover
spindle motor controls or the spindle servo drive electronics.

Sound familiar to anyone out there?
Thanks in advance.
Jeff