Sharp SF-A57 Service Manual page 34

[g] Original set sensor (DSS)
The DSS uses a photo interrupter which is integrated with a light emitting diode and a photo transistor. The signal is passed through the noise filter
composed of R23, C16, and Schmidt trigger invertor (IC4) to the gate array (IC7 53 pin), then passed through the data bus to the CPU.
Original set
sensor (DSS)
[h] Original width sensor (DWS)
The DWS uses a photo interrupter which is integrated with a light emitting diode and a photo transistor. When there is an original, the lever-type
actuator interrupts the optical path.
The circuit composed of Q12, R100, R29, and R47 is the connector disconnection sense circuit. When the connectors are not disconnected, the
base voltage (5V) of Q12 is divided by R100 and the LED of the photo interrupter to be about 1.2V, conducting the transistor.
At that time, the photo transistor is turned off under "paper empty" state, and the collector current of Q12 flows into R47.
Therefore, the signal DWS turns HIGH by the value (about 4.5V) obtained by dividing +5V with R49 and R47. When in "Paper present," the photo
interrupter turns ON and the collector current of Q12 flows into the photo interrupter. As a result, signal DWS turns LOW.
On the other hand, when a connector is disconnected, the base voltage of Q12 becomes +5V, turning off the transistor. Therefore, signal DWS turns
LOW and it is judged as "Paper present."
Signals are inputted through the noise filter composed of R33 and C21 to the gate array (IC7 54 pin).
Original width
sensor DWS
[i] Open/close switch (AUOD, FGOD, TGOD) input circuit (TGOD --- SF-A56 only)
This circuit senses open/close of the ADF unit, the paper feed guide, and the reverse guide, and is connected with three microswitches. Any switch
is closed when its open/close section is closed.
The FGOD directly opens/closes the power to the paper feed motor and the paper feed solenoid. If the FGOD is not closed, the power is not
supplied to the paper feed motor and the paper feed solenoid.
The AUOD and the TGOD are connected in series to +24V, and directly close the power to the drive sections except for the paper feed motor and
the paper feed solenoid. That is, the power is supplied to the drive sections except for the paper feed motor and the paper feed solenoid only when
the two switches (AUOD, TGOD) are closed.
When the paper feed guide open/close switch is turned on, +24V is applied to the cathode of ZD7, supplying the base current to Q8, conducting Q8,
supplying an open/close signal (a close signal in this case) to IC7 57 pin.
Operations in the other open/close switch circuits are the same as above, and each open/close signal is inputted to IC7.
R44 and C40 form a snubber circuit which absorbs an induced voltage generated when the open/close switch is opened during rotation of the DC
motor.
ADF open/close
switch AUOD
Reverse guide
open/close switch
TGOD
Paper feed guide
open/close switch
FGOD
TLP1240(C5)
VCC CN2-1
VOUT CN2-3
GND CN2-2
Original set sensor input circuit
TLP1240(C5)
173981-9
VCC CN3-7
VOUT CN3-9
GND
CN3-8
Original width sensor input circuit
DC+24V DC+24V
CN30-2 CN5-8
AUOD AUOD
CN30-1 CN5-7
AUOD AUOD
CN31-1 CN7-1
TGOD TGOD
CN31-2 CN7-2
DC+24V DC+24V
CN29-2 CN5-6
FGOD FGOD
CN29-1 CN5-5
Open/close switch input circuit
+5V
R101
180
173981-9 R115
15K
+5V
DSS
GND
+5V
R100
180
Q12
FN1L3M
+5V
DMS R29
GND
15K
DC+24V
Q7
ZD6
18V
FA1L3N
ZD5
18V
FD+24V
ZD7
18V
R44
4.7
C40
47µ F
PGND
– 33 –
IC4-4
R23
9 8
53
P0
10K
C16
TC74HC14AF
0.010µ F
TP24
R33 R34
10K
10K
C21
R47
0.010µ F
150K
R13 R40
10K 10K
Q11
FA1L3N
Q8
FA1L3N
G/A
(IC7)
G/A
(IC7)
54
P1
+5V
G/A
(IC7)
R12
10K
56
P3
55
P2
57
P4