| 摘要 |
PROBLEM TO BE SOLVED: To detect defects of plural lasers at low cost by generating a horizontal synchronizing signal error signal if horizontal synchronizing signals as many as the plural lasers are not counted within a horizontal signal permissible range. SOLUTION: A video controller 102 transmits a VDO signal of image data of one line to a laser driving circuit 104 in synchronism with a BDO signal. A laser driving circuit 104 turns on and off a laser diode 105 according to the VDO signal to form an electrostatic latent image on a photosensitive drum. In an engine controller 103, a BD signal counting means 112 is provided and counts the pulses of the BD signal sent from an optical sensor 111. The engine controller 103 counts the pulses of the BD signal inputted within a BD permissible range to make the horizontal synchronizing signal ready when two BD signals are inputted within the BD permissible range and generates a horizontal synchronizing signal error when only one BD signal is inputted within the BD permissible range. |
