Power-Off Timer Circuit - Epson Stylus COLOR 440 Service Manual

EPSON Stylus COLOR 440, 640, and 740

Power-Off Timer Circuit

The timer IC measures how long the printer is turned off. When the
printer is turned on, the IC sends the power-off time to the gate array.
The power-off time determines how extensively the printhead is cleaned
at power-on.
In the Stylus COLOR 440 and 640, an external crystal oscillator (CR1 or
CR3) provides the basic timing pulse. In the Stylus COLOR 740, the
oscillator is built into IC8, the same chip that contains the reset circuit.
Since the crystal's oscillation produces an analog waveform, the timer
IC converts it into a square wave to enable it to be processed digitally.
When the printer is on, power is supplied to the timer through the 5-volt
power bus. When the printer is turned off, a 3-volt lithium battery
powers the chip. Diodes on the power supply line prevent the battery
from charging when the printer is on, and from discharging back into the
power line when the printer is off.
CR1
+5
C4
D1
D7
0.1u
Batt1
Figure 2-26. Timer Control Circuit for Stylus COLOR 440
S-3510ANF
(IC5)
2
X O
3 5
CS
X I
8 6
VCC /SCK
4 7
GND /SIO
RM7
E05B44
(IC2)
123
TCE
121
TCLK
124
TDATA
CR3
+5
C4
D4
D1
0.1u
Batt1
Figure 2-27. Timer Counter Circuit for Stylus COLOR 640
Figure 2-28. Timer Counter Circuit for Stylus COLOR 740
Chapter 2 Operating Principles
S-3510ANF
(IC10)
2
XO
3 5
CS
XI
6
8
VCC /SCK
4 7
GND /SIO
RM7
E05B43
(IC2)
125
TCE
123
TCLK
126
TDATA
58