Reset Circuits - Epson Stylus Photo Service Manual

2.2.2.1 Reset Circuits

On the C209 main board, 2 ICs are mounted ; IC for monitoring the logic line(+5V) and IC for monitoring
the power line(+42V) and both are monitored by the gate array and CPU.
The reset circuit prevents the CPU from running away, which is caused by the unstable voltage in the
logic circuit during the power ON/OFF. Also, this circuit monitors the level of power voltage at the
overloading or malfunction on the circuit and manages the printer to operate normally, keeping the
damage to the printer minimum during the abnormal situations.



+5V Line Reset Circuit
In the +5V reset circuit, IC8 PST592D monitors +5V voltage and outputs reset signal from
VOUT to CPU and gate array when the abnormal voltage is detected. IC8 starts operating under
the following conditions.

When the power is turned on, a reset signal is output for 100ms after the +5V line level rises to
+4.2V.

During the print operation, if the +5V lines goes below 4.2V, a reset signal is output.
The reset signal does not go off until 100ms passed after the +5V line voltage level recovers
to 4.2V, as described above.



+42V Line Reset Circuit
In the +42V line reset circuit, IC9 M51955B monitors the voltage of +42V line in the port IN and
feeds back information to CPU. When the +42V line goes below +33.2V, IC9 outputs the reset signal
to the CPU port /NMI from the port OUT which is in the power off state. When the +42V line reaches
33.2V, the reset signal is released from the port of IC9 and is detected in the port 15 of CPU.
Rev. A
Figure 2-20. +5V Line Reset Circuit
Figure 2-21. +42V Line Reset Circuit
Chapter2 Operating Principles
2-21