Epson Stylus Color 440, Service Manual

Page: 68 / 212

EPSON Stylus Color 440/640/740 Revision A
Chapter 2 Operating Principles 68
[C257 Main for Stylus Color 640]
The reset circuit prevents the CPU from running away, which is caused
by the unstable voltage in the logic line during the power ON/OFF
operation. And reset IC(IC8) monitors level of power voltage at the over
loading or malfunction on the circuit and manages the printer to operate
normally, keeping the damage to the printer minimum during the
abnormal situations. On the C257 main board. The IC 8 has 2 functions
both the timer counter and creating a reset signal.
Figure 2-22. Reset Circuit for Stylus Color 740
2.2.4.2 Sensor Circuits
The following sensor circuits are mounted in the Stylus Color 440/640/
740 and selects appropriate operations based on the returned status.
ASF Sensor (Photo):
An ASF sensor detects the position of return lever when the power
is turned on, and causes the paper to be picked up by the pick up
roller from the normal initial condition. (Refer to section 2.1.1.3 for
detail.)
PE Sensor (Photo):
A PE sensor determines if there is paper in the printer. Based on the
signal form this sensor, a particular paper edge treatment such as
Micro-weave printing is performed.
HP Sensor (Photo):
A HP sensor detects the carriage home position. It is used for
managing printing position and cleaning, etc.
Thermistor Sensor
A thermistor sensor keeps stable printing quality, changing PZT
drive voltage(VH) slightly according to changes of environmental
temperature.
Cartridge Sensors:
Cartridge sensors are built into the Bk, CMY cartridge on the
carriage unit respectively to determine if the cartridge is installed or
not when it is exchanged or the power is turned on. In case of Stylus
Color 440/640/740, the counter is reset at every time the cartridge is
removed.
/NMI
MRES
/RESET
IC 1
C90A05
/RES
B1
10
3
2
29
24
25
+42 VIN
VDD
VBK
GND
/VDT
FRST
/RST
CE
SCLK
DATA
IC 8
RTC-9810
IC 2
E05B588