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

 

+35 V monitor circuit sets the pulse length of the head drive signal. If the voltage of the +35 V line

 

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.

 

CPU (1C)

 

P55

 

 

 

CRHOME

-.

 

 

 

 

 

 

P52

 

 

 

PE FRONT

 

 

 

 

 

 

 

 

 

 

 

P53

 

 

 

PE REAR

 

 

 

 

 

 

 

 

 

 

 

 

P34

 

 

 

PG

 

 

 

 

 

 

 

 

 

 

 

 

P31

 

 

 

RELEASE

 

 

 

 

 

 

 

 

LEVER

 

 

 

 

 

 

 

 

 

 

 

 

 

 

P51

 

 

+35

Voltage Monitor

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

P50

 

 

 

Head Temperature

+35 v

 

 

 

 

 

 

 

 

 

Vref

 

 

 

 

 

 

 

 

Vref

 

 

 

 

ZDl

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 6-26. Sensor Circuit Block Diagram

6-26

Epson FX-8700 170