Service manual

FO-2970MU
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 imped-
ance 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.
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.
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 proc-
ess, but also when the laser beam is emitted as image data, ASIC
controls and the signal is outputted from video terminal.
IC602
7805
IN
1
OUT
3
GND
2
+
CN603
BD
+5VL
1
SYNC-
2
GND
3
4 21
3
IC601
IR3C07
OUT
1
IM
3
Cp
2
GND
4
INH
5
So
6
Vcc
7
Vps
8
+
CN604
BD
+5VL
1
SYNC-
2
GND
3
D602
LNC702
LDPD
IC603
BU4S66
Vdd
5
CONT
4
I/O
1
O/I
2
GND
3
CN602
PM
GND
1
PMD-
2
+24V
3
PMCLK
4
GND
5
CN601
LSU
+24V
1
GND
2
VIDEO
3
SAMP
4
SYNC-
5
APCSTT
6
PMCLK
7
PMD-
8
PE
9
+24V
+24V
+5VL+5VL
+5VL
+5VL
+5VL
+5VL
BD CIRCUIT
APC CIRCUIT
R603
30K
Q601
A1015
R604
820
D601
PD481PI
Q602
C1815
R605
240
C602
0.1uF
C601
47uF/10V
C603
0.1uF
R601
130ohm/2W
R613
180
VR601
15K
R607
1K
PD601
GP1S53
C608
4700p
R608
30
C607
2200p
R606
10K
R609
10K
C606
220uF/10V
C605
0.1uF
R610
9.1
Q603
A1206
R611
750
R612
510
Fig. 9
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