Hardinge hcnc spindle problems before refit to Emc

Just about to start a refit to a Hardinge HCNC , but at the prescent time it's developed a fault on the spindle
the spindle is hunting back and forth , this becomes faster , to the point that after 30 sec's or so it blows 2 out of the 3 main 3phase fuses , as you can appriciate this becomes expensive on fuses ! .

any ideas anyone ?
it's fitted with a Inland Drives 6phase SCR servo board and Fanuc 16b controller at the moment , but once i have the spindle sorted , the changeover to EMC will begin .
with thanks to info from BigjohnT ! , the conversion looks a peice of cake in comparison to sorting the spindle .

i'm presuming either a major problem , or could just be adjustment of the servo amp and Tacho etc .
But any pointers appriciated

Dave