Yes, if you can't raise the voltage with the field grounded after re-polarizing, there's an internal problem with the generator- - - -possibly a bad armature or an open field winding. Can you see the brushes? Sometimes just sanding the armature where the brushes ride and installing a new set of brushes can "wake the dead"
Good luck!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!