Sensor Circuits - Epson FX-870 Service Manual

Principles of Operation

Sensor Circuits

The FX-8'70/1170 printer has the following sensors: CRHOME, PE (FRONT), PE (REAR), PG
(platen gap), RELEASE LEVER(RL), and HEAD TEMPERATURE. All the sensors are mechanical
switches, except the rear PE sensor, which is a photo diode, and the HEAD TEMPERATURE
sensor, which is a thermistor.
In addition to the sensor circuits, a +35 V monitor circuit and a Vref circuit are also provided. The
drops below approximately +31 V, the printer stops printing for a while. As soon as the voltage
recovers, the printer starts to print at halfspeed. (The PF motor also slows down.) The Vref circuit
supplies 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 6-26 shows the sensor circuit block diagram.
6-26
CRHOME
P55
P52
PE FRONT
P53
PE REAR
P34 PG
RELEASE
P31
LEVER
P51 P51
Head Temperature Head Temperature
Vref Vref
Vref Vref
Epson FX-8700 170