Sharp ER-A440 Service Manual page 21

<Motor lock protection>
When an abnormal load is applied to the mechanism, the DP (Dot
Pulse) frequency is checked to prevent against the motor burn-out,
the timing belt shift, and gear damage. If the following condition is
made, the CPU stops the motor rotation.
When starting the motor: When the cycle from starting to the
100th pulse of DP is 16ms. (The one pulse cycle of DP is normally
555us.)
During constant rotation of the motor: When one pulse of DP is
1100us or more.
4) Printer sensor circuit
+5V
R207
HP
Q6
C93
CPU
+5V
R132
RJTMG
Q8
C91
+5V
R1134
RJRST
VPS
MPCA7
The printer supplies the RP (Reset Pulse) signal, the HP (Home
Position) signal, and the DP (Dot Pulse) signal) to control printing
timing and conduction timing of solenoids. It also supplies the VPJ
signal to detect the presence of validation paper. These sensor are
photo interrupters.
RP (RJRST) signal
This signal is outputted once for every reciprocating motion of the
print head. It indicates the reference position of the HP signal.
The rear edge of RP (OFF -- ON) is used as the signal.
HP signal
The pulse signal is outputted from the slit in the disk installed to
the DC motor shaft. It is used as the reference signal for starting
counting of the DP signal. It is generated once for twenty DP
signals. The rear edge of the HP signal (ON -- OFF) immediately
after generation of the RP signal is used as the signal.
DP (RJTMG) signal
The pulse signal is outputted from the slit in the disk installed to
the DC motor shaft. It is used as the control signal for the print
solenoid and the paper feed solenoid.
The front edge of the output signal (ON -- OFF) is used as the
signal.
VPJS (VPJ) signal
The presence of a validation card is detected by interruption of the
photo interrupter LED light by the validation card.
R206
HP
R126
R131
R129
DP
R130
R133
RP
C228
VPJS(NU)
Relation ship among RP/HP/DP
RP
HP
OFF
DP
ON
* The waveforms are those indicated with arrow in Fig.3-3.
5) Dot solenoid drive circuit
+5V
+5V
VRESC
+5V
DOT1
~DOT4
+5V
DOT5
~DOT7
MPCA7
The DOT1
NOT USED
are pulled up by the VRESE and converted into LOW by the driver IC.
A +24V voltage is applied to the solenoid. This operates the dot wire.
6) Paper feed circuit
VRESC
MPCA7
The PFJ0 (the journal paper fed signal from the MPCA7) and the
PFR0 (the receipt paper feed signal) are pulled up by the VRESE and
converted into LOW level. A +24V voltage is applied to the solenoid.
This operates the paper feed solenoid.
4 – 14
OFF
OFF
20 cycles of DP (TYP.11.1ms)
555µs(TYP.)(516~590µS)
+5V
R145
R146
Q9
R149
R152
IC15
R153
R155
IC16
DOT7 (the dot solenoid drive signals from the MPCA7)
+5V
R145
R146
Q9
IC16
R156
PFJ0
PFJ0
R161
Q11
PFR0
+5V
ON
GND
The first HP after turning
1.5ms or above
OFF/ON RP.
+5V
ON
GND
50µs above
50µs above
+5V
GND
#1 #2 #3 #4
Print area
+24V
DOT1~DOT4
DOT5~DOT7
+24V
F2
IC18
PFR0