[en] The trajectory and envelope of the ion beam in a cyclotron are determined by the magnetic and electric fields. The magnetic field between the cyclotron is controlled by the currents through three types of coils: main, trim and harmonic coils. In the acceleration region, the field is adjusted for each ion beam using main and trim coils. The harmonic coils are used far fine adjustment of the magnetic field in the central and extraction region of a cyclotron. It has been shown that small error in positioning of the magnetic structure elements-sectors (1 mm. i. e. 0.14 % with respect to the relevant sector dimension) could cause beam orbit distortion of 0.6 mm in the extraction region. This distortion is three times smaller but is not negligible compared to the designed orbit perturbation caused by the harmonic coils. Therefore, to minimize undesired perturbations of the ion beam orbit, special attention must be devoted to the sector positioning during mounting process (author)