Minor repair: involves the maintenance work of post operators or a small number of professional maintenance personnel.
Medium repair: maintenance work (often divided into minor repairs and daily maintenance) completed by a large number or a small number of multi-type professional maintenance personnel.
Overhaul: a comprehensive overhaul that requires most or all production lines to stop production.
I don't have the specific content of "seeing, listening and asking" involved in all kinds of maintenance, and I'm also taking a big break.