Service manual
.
REV.-A
2.3.3 Sensor Circuits
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.>
~
The FX-870/l
170
printer has the following sensors:
CRHOME,
pE
(FRONT),
pE
(REAR),
pG
(platen
9ap),
RELEASE LEVER, and HEAD TEMPERATURE. All the sensors are momentary switches, except the PE (REAR)
sensor, which is a photo diode, and the HEAD TEMPERATURE sensor, which is a thermistor.
In addition to the sensor circuits, the +35 V monitor circuit and the
Vref circuit are also provided. The +35 V
monitor circuit is used to set the pulse length of the head drive signal. If the voltage of the +35 V line drops
below
+31
V (approx.), the printer stops printing fora while. As soon
asthevoltage
recovers, the printer starts
to print at a half speed. (The PF motor also slows down.) The
Vref circuit is used to supply the reference voltage
for the A/D convertor in the CPU.
The CPU constantly monitors the printhead temperature. If the printhead temperature exceeds the maximum
level, the printer stops printing until the temperature drops to a certain level. When the
printhead temperature
cools down, the printer resumes printing automatically.
Figure 2-26 shows the sensor circuit block diagram.
.
>
..-.
CPU
(lC)
CRHOME
PEFRONT
PEREAR
PG
~
+35
v
RELEASE
LEVER
+35 Voltage Monitor
Head Temperature
+35
v
Vref
ZD1
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7)7
Figure 2-26. Sensor Circuit Block Diagram
2-26