Epson 680Pro - LQ B/W Dot-matrix Printer Service Manual page 48

EPSON Stylus COLOR 680/777/77i
2.2.2.7 Sensor Circuit
C383 MAIN is equipped with the following two sensors to detect the status of the
printer. Unlike the previous product, ASF HP sensor is not equipped on the ASF and
the ASF HP is determined with the clutch mechanism (2.1.4 Paper Feeding
Mechanism).
o HP/PE Sensor
This sensor uses photo interrupter method and detects the following three status.
The photo interrupt component and two detection levers consists of this sensor.
n CR home position
The CR home position is detected on the right edge of the CR shaft with the
HP/PE sensor during the power on sequence. In case the CR home position is
detected in the power on sequence, this sensor outputs HIGH signal to the
CPU.
When the LOW signal is output to the CPU in the detection position, the CR
unit is out of home position.
n Paper Top & End position
When the Paper is in the paper path, this sensor outputs the HIGH signal.
When the Paper is not in the paper path, this sensor outputs the LOW signal.
This status is always monitored during the printer is in the power on status
with this sensor.
o Thermistor (THM)
The thermistor is attached directly on the printhead driver board. It monitors the
temperature around the printhead and determines the proper head drive voltage
according to the ink viscosity that varies by the temperature. This information is
fed back to the CPU analog port. When the temperature rises, the head drive
circuit lowers the drive voltage: When the temperature lowers, the head drive
circuit rises the drive voltage.
The block diagram for the sensor circuit is shown below
Operating Principles
:
Electrical Circuit Operating Principles
Figure 2-23. Sensor Circuit Diagram
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