| 摘要 |
PURPOSE:To prevent a defective picture by detecting an improper number of revolutions of a polygon motor. CONSTITUTION:A number of revolutions of a polygon motor 3b is controlled in response to a frequency division ratio of a frequency divider 12, and the motor 3b is locked by a phase comparator 14 and a phase difference voltage conversion circuit 15. A synchronizing signal is detected from a laser beam scanned by a polygon mirror 3a and the number of revolutions of the polygon motor 3b is detected by counting the synchronizing signal with counters 201-206. A CPU 13 allows an operating section 19 to warn a defect of a PLL as a display when the count of the counters 201-206 is defective. |
