Sharp AM-900 Service Manual page 86

AM-900U
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.
2.2.4 Hardware controlled protection function
Device Protective action
Heater lamp (fusing 1 The heater lamp is
device) forcibly turned off
when the temperature
of the fusing device
(thermistor value)
exceeds the upper
limit.
Laser (LSU) 1 When the cover is
open, the power sup-
ply to the laser system
circuits is shut off.
2 When the polygon
motor is inactive, the
VIDEO signal is dis-
abled (lighting prohib-
ited).
3 The sampling of S/H
signal is disabled
unless the VIDEO sig-
nal is active (laser on).
A fuse is installed in the following power supply lines: Optical unit (LSU) laser, Main motor, Pickup motor
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
b) The laser beam drive block
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.
Circuit description
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.
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.
Equipped with a circuit for
enabling output of the VIDEO sig-
nal when the polygon motor drive
signal PMD is received.
Equipped with a circuit for
enabling output of the S/H signal
when the VIDEO signal is
received.
5 – 13
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.
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).
Purpose
Avoiding the abnormally
high temperature of the
fusing device.
Avoiding the exposure to
laser beam.
Preventing the laser
beam from focusing on
only one point on the
drum.
Avoiding abnormally high
output of the laser.
Status to be activated
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.
Malfunction due to the digital
system circuit failure.
The polygon motor is stopped
while debagging.
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.