Sharp FO-2970M Service Manual - Page 48
Scanning motor ON/OFF signal.
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FO-2970MU f. Laser scanning unit This unit controls the laser beam power and laser beam scanning. The control is performed with the signals inputted outputted to or from the CPU and ASIC. +5VL BD CIRCUIT R603 30K D601 PD481PI Q601 A1015 R604 820 R605 240 Q602 C1815 CN604 1 +5VL 2 SYNC3 GND BD CN603 1 +5VL 2 SYNC3 GND BD +5VL + C601 47uF/10V IC602 7805 3 OUT C602 0.1uF GND 2 IN 1 R601 +24V 130ohm/2W C603 0.1uF +5VL IC601 IR3C07 Vps 8 Vcc 7 So 6 R606 10K 5 INH R609 10K 1 OUT Cp 2 IM 3 GND 4 APC CIRCUIT C607 2200p +5VL C608 4700p +5VL +5VL R613 180 R608 30 VR601 15K R607 1K 2 1 4 3 PD601 GP1S53 CONT 4 Vdd 5 + IC603 C606 220uF/10V 2 O/I I/O 1 GND 3 BU4S66 C605 0.1uF PD R610 9.1 Q603 A1206 R611 750 LD D602 LNC702 R612 510 CN601 1 +24V 2 GND 3 VIDEO 4 SAMP 5 SYNC6 APCSTT 7 PMCLK 8 PMD9 PE LSU +24V CN602 1 GND 2 PMD- 3 +24V 4 PMCLK 5 GND PM Fig. 9 1) Signal functions PMCLK Clock signal for driving the scanning (polygon) motor. (1.18KHz/770Hz) PMD Scanning motor ON/OFF signal. APCSTT Used to start the laser beam generation circuit. SYNC This signal is outputted when the laser beam scanned by the laser beam sensor signal is sensed by sensor (Photo diode D601). Used for the left margin control. VIDEO This signal is used to control the laser diode emitting. Not only when the laser beam is emitted to perform the LEND process, but also when the laser beam is emitted as image data, ASIC controls and the signal is outputted from video terminal. 2) Laser beam power control The laser beam power is controlled in the laser emitting unit PWB. This circuit functions to keep the laser beam output power at a constant level. The laser beam output is monitored with photo diode D602 for monitor. When the laser beam output rises above the specified value, the impedance of photo diode D602 is decreased to decrease the monitor input (3PIN) voltage of the laser diode control IC (IC601). Then the laser diode (LTO28GS) drive voltage is decreased to decrease the laser beam output to the specified level. When the laser beam output is decreased below the specified level, the contrary operation are performed. 5 - 12