1. power unit input fuse, since the input overload for too long, resulting in fuse protection, check whether the device has a long-term overload conditions, and the fuse corruption occurs, replacement of the fuse;

2. phase input line power unit abnormal, one-phase input line break, check if there is an input line disconnection;

3. power unit driver board anomaly, abnormality detection circuit board or drive failure, which can lead to failure;