Sharp AR-5012 Service Manual page 79

[When the heat roller surface temperature is lower than the set
level]
1) Since the thermistor terminal voltage is higher than the set level,
the HL signal from the CPU becomes HIGH.
2) The HL signal is turned to be the HLOUT signal through IC124 pro-
tect circuit, and inputted to the photo triac coupler on the power
PWB.
3) When the internal triac turns on, a pulse is applied to the gate of the
external triac. Consequently a current flow from the power source
through the heater lamp to the triac, lighting the heater lamp.
[When the heat roller surface temperature is higher than the set
level]
1) Since the thermistor terminal voltage becomes lower than the set
value, the HL signal from the CPU becomes LOW.
2) The HL turns LOW, the photo triac coupler on the power PWB turns
OFF, the external triac turns OFF, and the heater lamp turns OFF.
[In case of the thermistor open]
The voltage at IC120 6pin over the voltage at 5pin to drive the output
THOPEN at 7pin to LOW. This is passed to the CPU and the trouble
code "H2" is displayed.
(6) Toner supply motor drive circuit
The IC129 is the motor control IC, which generates the pseudo AC
waveform with the pulse signals (TM, TM-) outputted from ASIC, driv-
ing the toner supply motor.
(4-D3) (TM)
(4-D3) (TM_)
R204
47kJ
(7) Main motor drive circuit
The main motor is driven by the MMD signal from ASIC. While the
main motor is rotating, the MMD signal is driven to HIGH and passed
through IC125 to the control circuit in the main motor to rotate the main
motor. When the main motor speed reaches the specified rpm, the
MMLD signal is turned LOW and passed through IC115 to the CPU.
R187
1kJ
R188
R205 1kJ
47kJ
PGND
AR-5012 ELECTRICAL SECTION 13 - 9
(5) Driver circuit (Solenoid)
a. Outline
Since the load signal from the CPU or the ASIC cannot drive the load
directly, it is passed through the driver IC to drive the load.
b. Operation
The driver circuit forms a Darlington circuit with transistors. Therefore a
large drive current is obtained from a small current (ASIC output cur-
rent). When the driver input voltage (base resistance input) is HIGH
(+3.3V), the transistor turns ON to flow a current in the arrow direction,
operating the load. When the driver is ON, the driver output terminal
voltage is 0V.
ASIC/CPU
OUT PUT
IC129
17
Vcc
19 16
PSAVE VM
20 9
Rin OUT1
18 5
Fin OUT2
21
VREF
6
RNF
1 8
NC GND
2 FIN
NC FIN
3
NC
4 25
NC NC
7 24
NC NC
10 23
NC NC
11 22
NC NC
12 15
NC NC
13 14
NC NC
BA6920FP
PGND
MMD MMD
ASIC
CPU
+24V
LOAD
LOAD
24V
+
C212 C213
10u/35V
0.1u/50V
PGND
TMB_O
(9-A1)
TMA_O
(9-A1)
IC201
1 16
Main Motor
I1 O1
2 15
I2 O2
3 14
I3 O3
4 13
Control
I4 O4 /MMD
5 12
I5 O5
6 11
I6 O6
7 10 Circuit
I7 O7
8 9
COM NC
( Main Motor)
TD62503F
MMLD