| 摘要 |
PURPOSE:To make it possible to erase a recording medium approximately completely and to evaluate the defect of the recording medium so that the defects are classified into the defect due to the fluctuation in a polarization angle or the defect due to the fluctuation in reflectivity, by providing a solenoid, a turntable, optical sensor and the like. CONSTITUTION:A recording medium D is rotated in the direction A with a turntable 2, and a solenoid 1 and a detecting optical system is operated. A part of a track is instantaneously erased altogether by a magnetic field generated in the solenoid 1. The deflection angle and the intensity of light, which is transmitted through the track, and detected with an optical detecting system comprising optical sensors 8 and 9 and the like. When the recording medium D is completely erased, it is judged that the fluctuation in polarization angle, which is detected with the optical detecting system, is caused by the strain of a board. It is also judged that the fluctuation in intensity is caused by pinholes and the like. |
