Epson FX-870/1170 - Manual (Page 141)

Principles of Operation
Sensor Circuits
The printer has the following sensors: CRHOME, PE (FRONT), PE (REAR), PG
(platen gap), RELEASE 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 V monitor circuit and a Vref circuit are provided. The
V monitor circuit sets the pulse length of the head drive signal. If the voltage of the V line
drops below approximately 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 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.
P55
P52
P53
P34
P31
CRHOME
PE FRONT
PE REAR
PG
RELEASE
LEVER
P51 P51
Vref Vref
Head Temperature Head Temperature
Voltage Monitor Voltage Monitor
v v
Vref Vref
6-26 Epson 170