Sharp AM-900 Service Manual page 90

AM-900U
b) Laser Drive circuit operation timing
Laser drive circuit/LD Drive Circuit
nHSYNC
nLDEN
nVIDEO
nS/H
Laser output
Settling time/Settling Time
3ms above/More than 3ms
Fig. 12
c) Each signal injection timing of the scanner motor
24V
DC24V
0V
H
IN
CLOCK
L
H
nSTART
L
UNLOCK
Asynchronous
nREADY
OUT
LOCK
Min 1s
synchronous
UNCHECK
nREADY
CHECK
CHECK
signal monitoring
GO
Speed
Jitter etc.
STOP
Fig. 13
d) Laser Drive circuit interface
Pin No. Terminal I/O
4 nLDEN Input
2 nS/H Input
3 nVIDEO Input
1 GND -
5 GND -
7 GND -
6 +5V -
8 nHSYNC Output
(Open-
collector)
Laser OFF time/LD OFF Time
3µs following/Less than 3µs
APC correction time/Auto Power Control Time
10µs above/More than 10µs
Min 10 ms Min 10 ms
Min 0.1s Min 0.1s
Starting time
(Max 0.5s)
Min 10 ms
Min 1s
Function
Signal enables Laser driven
"H" : Disable
"L" : Enables
APC control signal
"H" : Hold
"L" : Sampling
Laser control signal
"H" : Laser OFF
"L" : Laser ON
GND
GND
GND
Power supply (+5V)
Horizontal synchronize signal
"H" : Asynchronous
"L" : Synchronous
3.1.4 Fusing unit control
The fusing section is heated by the heater lamp (500W). The heater
lamp is controlled (turned on/off) to keep the optimum temperature.
The following signals are outputted by the CPU and Logic circuit for
control.
1) Signal functions
• HLON
This signal is to turn on/off the heater lamp. When this signal is
outputted turn on triac TRA1. Then an AC power is supplied to
the heater lamp to turn on the heater lamp.
• RHT
This is the output signal of the thermistor which detects the sur-
face temperature of the heat roller. It is inputted to the CPU. The
heater lamp is turned on/off depending on the value of RTH volt-
age.
2) Protect against overheat
Though the heater lamp ON signal (HLON-) is normal, if triac TRA1
are kept ON, overheat may result.
To prevent against this, temperature fuses are used.
When the fusing roller surface temperature exceeds about 214
degrees C, the temperature fuse blows off to open the +24V power
line which drives the power relay RL1, opening the power line for
the photo triac TRA1. Therefore, the power is not supplied to the
heater lamp.
A temperature fuse is also provided in the heater lamp power line.
In case of overheating, the heater lamp power line is opened
directly.
3) Timing of temperature detection and heater control
As shown by the following timings, four values of software ther-
mistor voltage are input as A/D conversion values. The mean value
of two medians among these four is regarded as the newest ther-
mistor value (temperature).
• The value is compared with the temperature (200°C) control
value every 100 ms.
• If the value is higher than 200°C, the heater becomes OFF. If
lower, the heater becomes ON.
• The heater ON timing is in accordance with the timing of Power
Zero Cross interrupt.
Heater ON/OFF Control
Timings of thermistor value input and heater control
4) Heater control (Temperature control)
Control method
a) Base machine printing (Copy, List, Receiving)
• Temperature control is started when data to be printed are
produced (or when slips are to be prepared).
• Temperature is controlled at 200 °C. (Heater OFF over 200
°C. Heater ON below 200 °C.)
• After printing, temperature is not controlled. (Heater is not
turned ON.)
• Fan motor starts revolving from the beginning of temperature
control and stops 120 seconds after printing is finished.
5 – 17
Heater ON/OFF Control
T (x 10ms)
Inputting thermistor values
Fig. 14