The causes and manifestations of various defective states of parts and assemblies of mechanisms of cyclic action are considered. The problems arising from improper adjustment of components, the consequences of wear of parts, the results of poor-quality assembly and misalignment of mechanisms are considered. The results of the application of the proposed methods for detecting defective states are presented on the examples of the study of rotary tables with a worm gear, a rotary table with a locking mechanism of flat gears and a hydromechanical drive system.