Having a problem with my old Kitamura VMC DC spindle motor and/or drive.

Machine:

1981 Kitamura Mycenter-2
Fanuc 6MB control
Approx 7 hp DC spindle motor w/ Fanuc 3 spindle drive
Running on 3 ph. rotary. conv. with about 5% imbalance

Problem:

This just arose this week after several years of fairly reliable service...

While manually jogging to face off a workpiece, the spindle drive will fault.
Checking the drive showed that one of indicator fuses and its 35A partner had blown.

Replaced the fuses...cleaned the motor brushes.

Every OK for next 16 hrs of run time.

Today same thing happens to adjacent fuses.

I noted that the fault occurs precisely with pressing the Y-axis travel key (first time in the + dir, 2nd in the -dir)

I pulled the Y-axis brushes....they were very dusty w/carbon. Now cleaned.

I will reclean the spindle brushes/commutator, as well as the rest of the servo brushes.

But...can the servo brushes cause the problem with the spindle fuses??

Thank you.