He is diagnostic about the machine

diagnostic

– adjective
1.of, pertaining to, or used in diagnosis.
2.serving to identify or characterize; being a precise indication.

–noun
3.diagnosis (def. 1).
4.a symptom or characteristic of value in diagnosis.
5.Medicine/Medical. a device or substance used for the analysis or detection of diseases or other medical conditions.
6.Computers. - a.a message output by a computer diagnosing an error in a computer program,computer system, or component device.
- b.a program or subroutine that produces such messages.