1. After the first outside: the use of hope, listen, smell, ask, touch and other methods from the outward internal inspection;
2. After the first mechanical electrical: mechanical failure is easier to observe, and CNC system fault diagnosis is more difficult;
3. First static after the move: maintenance personnel to do the first static after moving, the machine fault also need to first static and then move;
4. Public after the first special: To solve the main contradictions, and then solve the local, secondary contradictions;
5. Simple before complex;
5. After the general special: in the exclusion of a fault, first consider the most common possible causes, and then analyze the special causes of rare occurrences.