Service manual

FO-IS125N
5 – 23
3.1.3 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 Logic circuit.
1) Signal functions
2) Laser beam power control
The laser beam power is controlled in the laser scanning unit.
This circuit functions to keep the laser beam output power at a con-
stant level.
The laser beam output is monitored with photo diode for monitor.
When the laser beam output rises above the specified value, the
impedance of photo diode is decreased to decrease the monitor
input voltage of the laser diode control IC.
Then the laser diode 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.
3) Timing of scanning
a) Scanning motor interface
Fig. 9
Fig. 10
Lens
Lens
Polygon mirror
Polygon motor
Laser
Photodiode
LD PWB
Lens
Laser diode
Laser scanning unit (LSU)
Laser start
position sensor
Scan
Laser
Photodiode
Laser diode
Laser diode driver
LD PWB
Polygon motor
Amp.
Laser
Motor driver
nHSYNC
nLDEN
nVIDEO
nS/H
CLOCK
nREADY
nSTART
GND
+24V
+5V
GND
Motor
Laser Scanning Unit (LSU)
Polygon motor
Polygon mirror
1
2
3
4
5
4
3
2
6
1, 5, 7
8
PMCLK
Clock signal for driving the scanning motor. (2659.57Hz)
PMD
Scanning motor ON/OFF signal.
HSYNC
This signal is outputted when the laser beam scanned by the laser
beam sensor signal is sensed by sensor (Photo diode).
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 pro-
cess, but also when the laser beam is emitted as image data, Fax
Engine (IC100) controls and the signal is outputted from video ter-
minal.
Fig. 11
Pin No. Terminal I/O Function
1 CLOCK Input Clock input
2 nREADY Output Motor rotation detect signal
"L": Synchronous
"OPEN": Asynchronous
3 nSTART Input Motor control signal
"L": Start
"OPEN": Stop
4GND-GND
5 +24V - Power supply (+24V)
Laser
nHSYNC
ON
OFF
Non-Active
Active
16.26mm
27.88µs
216mm
370.34µs
1 LINE
328.95mm
564.0µs
>3.75mm
>6.43µs
1.0µ s max.
Effective printing width
Effective width of printing data
F-number/Focal Length:104.7mm
VIDEO CLK:13.7774MHz
Polygon rotation speed/Rotation speed:26595.7min
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