Epson Stylus COLOR 900 Service Manual page 53

EPSON Stylus COLOR 900/900N
2.3.4.1 Power-Off Timer/Reset Circuit
The RTC9810 produces a reset signal by monitoring both the 5 VDC
line (input to pin 7) and 42 VDC line (input to pin 9). When the voltage
level for the 5 VDC line is below 4.3 V, or the voltage level for the
42 VDC line is below 35.5 V, the circuit outputs a reset signal from
pin 2. This occurs, for example, when the printer is first turned on, and
serves to reset the logic chips to prevent abnormal operation of the
driver systems.
Voltage Divider
The reset chip also includes an internal timer circuit (oscillator) to keep
track of how long the printer has been off. This lets the printer determine
whether to perform a cleaning cycle at the next power-on, and, if so,
which type of cleaning to perform.
While the printer is on, it supplies 5 V at pin 7 to operate the internal
timer circuit; however, when the printer is off, a 3-volt lithium cell battery
powers the timer circuit through pin 8.
Drops to 3.5 V
Power-Off Timer/Reset Circuit
Figure 2-14.
Chapter 2 Operating Principles
48