Epson Stylus Photo 720, Service Manual

Page: 50 / 154

EPSON Stylus Photo 720 / EPSON Stylus Photo EX3 Revision A
Operating Principles Electrical Circuit Operating Principles 50
2.2.2.7 Sensor Circuit
C301MAIN is equipped with the following five sensors to detect the status of the
printer.
o
HP Sensor
HP sensor uses photo interrupter method. HP sensor detects the carriage HP (home
position). HP is the standard position for the print start position. When CR unit is
within the home position, the sensor o5V: When CR unit is out of the
home position, the sensor outputs 0V.
o
PE sensor
PE sensor uses photo interrupter method. PE sensor detects paper on paper path of
the printer. If paper passes, PE sensor outputs 0V. If there is no paper, the sensor
o5V. The signal output from this sensor and the stepping pulse of PF
motor determines the paper top position and the bottom position and it is reflected
to the printable area of paper feed direction.
o
ASF HP sensor
ASF HP sensor uses photo interrupter method. This sensor consists of the ASF HP
detector wheel, which is attached on the ASF LD roller shaft, and a photo sensor.
The ASF HP detector wheel has a small window and when this part is positioned
between photo sensor terminals, the sensor detects ASF HP. When this window is
within the ASF HP, the sensor outputs 0V, and when it is out of ASF HP, +5V is
output. This sensor detects the ASF return lever position at the power on and
detects standby state of the ASF LD roller.
o
Thermistor (TH)
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 ASIC 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.
o
Black/ Color cartridge sensor (COB/ COC)
Cartridge sensor uses mechanical method. This sensor detects whether a black or
color ink cartridge is installed in the CR unit. When an I/C is installed, this sensor
outputs 0V: When no I/C is installed, the sensor o5V.
The block diagram for the sensor circuit is shown below:
Figure 2-19. Sensor Circuit Diagram
+5V
+5V
PE
PEV
H P
GND
GND
GND
H PV
A SF
GND
A SFV
+5V
+5V
+5V
+5V
+5V
+5V
+5V
5
2
3
TH M
coc
79
80
105
Black I/C sensor
Color I/C sensor
Head thermistor
IC2
E05B70**
IC1
H064F2328F
SW A2
SW A0
SW A1
SW C0
SW C1
CPU
AN0
CN9
Head FFC
CN5
PE Sensor
CN4
CR HP Sensor
CN6
ASF HP Sensor