AM-400 (serv.man5). Chapter 5 (Circuit Description). - Sharp Copying Equipment Service Manual (repair manual). Page 13

AM-400DE

5 – 13

1) Main Motor control: Control the rotation of Main Motor and its

mechanism

Main Motor is the stepper motor and drives the whole of the mech-
anism of LBP. Main Motor is driven in 2-phase excitation by the
driver (IC34: A3982SLB). The driver circuit is provided with the fuse
(F7) to shut the motor power supply for the safety.

2) Pickup Motor control: Control the rotation of Pickup Motor and its

mechanism

Pickup Motor is the stepper motor and drives the pickup mecha-
nism of print paper. Pickup Motor is driven in 2-phase excitation by
the driver (IC32: ULN2003A). The driver circuit is provided with the
fuse (F6) to shut the motor power supply for the safety. Printer CPU
controls the timing to pickup the paper with watching the roller sen-
sor.

3) Fuser control: Control the temperature of the fuser unit

The heater lamp is controlled ON/OFF to adjust the temperature of
the fusing unit. The heater lamp is driven by the driver (IC32:
ULN2003A). The temperature of the fusing unit is monitored with
the thermistor. The fuser control circuit is provided with the safety
circuit to stop to light the heater lamp automatically when the ther-
mistor detection temperature rises over unusual high temperature. 

4) High Voltage Generator control: Control high voltage supplied to

LBP
• Main charger voltage to the drum unit
• Developing bias voltage to the toner unit
• Transfer charger voltage to the transfer roller

The high voltage outputted from High Voltage unit is controlled with
PWM and ON/OFF signals ("MCON" and "TCON").

5) Laser Scanning control: Control Optical unit (LSU) to expose the

OPC drum.

The laser beam scanning light expose the OPC drum correspond-
ing to the print data. The circuit of Optical unit (LSU) is composed
with the scanning motor drive block and the laser beam drive block.

a) The control of the scanning motor drive block

The scanning motor is controlled by the clock of 2659.574Hz
("PMCLK") and ON/OFF signal ("PMD"). Optical unit (LSU)
replies by the ready when the rotation of the motor becomes
stable. The initialization of the laser beam control is started after
the stable rotation of the scanning motor is confirmed.

b) The laser beam drive block

The timing of the signals is controlled in accordance with the
specifications of Optical unit (LSU). Main CPU (IC1: OA-2000)
outputs the print data ("PDATA") synchronized in the horizontal
synchronous signal ("SYNC") from Optical unit (LSU). The print
data is generated by Main CPU is directly transferred to Optical
unit (LSU).

6) Sensor monitor: Monitor each sensor

Printer CPU controls the timing of the printing action with the follow-
ing sensor information, and detect the paper jam, the paper empty
and the paper size.

a) PIN: Detect carriage position of the paper

b) POUT1: Detect carriage position of the paper

c) POUT2: Detect carriage position of the paper

d) PEBY: Detect the paper on the bypass tray

e) OPEN_TRAY: Detect the tray cover setting

f) TCT2~0: Detect the toner cartridge setting

7) Communication with Main CPU

The printer information is communicated with Main CPU. At first,
Main CPU transfers the command to Printer CPU on serial commu-
nication I/F. Then, the action according to the command is exe-
cuted, e.g. start printing and return the status of the printer.

A fuse is installed in the following power supply lines: Optical unit (LSU) laser, Main motor, Pickup motor

Heater lamp (fusing 
device)

1 The heater lamp is 

forcibly turned off 
when the temperature 
of the fusing device 
(thermistor value) 
exceeds the upper 
limit.

The circuit forcibly turns off 
(resets) the relay control signal of 
the heater lamp when the ther-
mistor value reaches 238 ± 6 

°C. 

To turn on the heater lamp again, 
it is necessary to have the micro-
computer change the relay con-
trol signal PWRLY from 0 to 1. In 
other words, once the protective 
action is performed, the protec-
tion is not canceled automatically 
even if the temperature detected 
by the thermistor decreases.

Avoiding the abnormally 
high temperature of the 
fusing device.

The protection is activated 
when F/W is out of control, the 
microcomputer ADC is defec-
tive, or other abnormality 
occurred. Normally, the heater 
lamp is turned on/off by moni-
toring the temperature using 
F/W.

Laser (LSU)

1 When the cover is 

open, the power sup-
ply to the laser system 
circuits is shut off.

Equipped with a regulator circuit 
for producing the laser system 
power (+5 V) supplied to the LSU 
from +24 V power supply inter-
rupted by the interlock.

Avoiding the exposure to 
laser beam.

Malfunction due to the digital 
system circuit failure.

2 When the polygon 

motor is inactive, the 
VIDEO signal is dis-
abled (lighting prohib-
ited).

Equipped with a circuit for 
enabling output of the VIDEO sig-
nal when the polygon motor drive 
signal PMD is received.

Preventing the laser 
beam from focusing on 
only one point on the 
drum.

The polygon motor is stopped 
while debagging.

3 The sampling of S/H 

signal is disabled 
unless the VIDEO sig-
nal is active (laser on).

Equipped with a circuit for 
enabling output of the S/H signal 
when the VIDEO signal is 
received.

Avoiding abnormally high 
output of the laser.

When F/W under develop-
ment is defective or runs out 
of control, the protection is 
activated. Normally, each sig-
nal is controlled following the 
sequence by F/W.