I recently bought a second hand feeler ftc280 lathe. The spindle makes me troubles. If I switch from automatic mode to edit, the spindle turns backward. Then suddenly it started, if it runs above 1500 RPM when an M05 is commanded the spindle slows down rapid to about 200 RPM, from there it runs out without brake. Only when it stands, about 15 seconds later the nc-program continues.

Somebody ever experienced this or something similar before?

Your help is greatly appreciated