Epson SEIJ98006 Service Manual page 57

EPSON Stylus Color 900
Once the Q1 is off, the energy charged in the primary side flows into the
secondary side all at once. This occurs because the energy transfers in
the same direction as the reverse diode characteristics with the Q1 off.
The secondary side of the transformer (T1), which has the specified
numbers of coiling lines for 42 VDC production, creates the 42 VDC out
of the energy led to the secondary side by the electromagnetic
induction.
The secondary side has numbers of stabilizing circuits to output
stabilized voltages, as listed below:


Smoothing circuit:
Since the energy led from the transformer (T1) to the secondary
side by the electromagnetic induction is alternating current, it
must be smoothed by the electrolysis condensers C51 and C52
to be direct current.


+42 V line constant voltage control circuit:
7 zener diodes (ZD51, ZD81 - ZD86) connected in series
monitors +42 V status used to drive various mechanisms. To
keep the output voltage at a constant levelI, the circuit controls
the on/off timing of the Q1 slightly according to the signals fed
back from the photocoupler (PC1).


+42 V line overvoltage protection circuit:
This circuit includes 2 zener diodes (ZD52, ZD87) connected in
series. It monitors the +42 V line used to drive various
mechanisms to detect abnormal rise in the voltage level caused
by a defect in the circuit. If the output voltage rises to +48 V, the
signal is input to a port of one of the 2 channels in the
photocoupler (PC1) to completely cut off the Q1 operation. Once
this circuit is active, a normal flow does not recover unless the
printer is turned off and back on.


+5 VDC production circuit:
L4960 (IC51) produces +5 VDC out of +42 VDC. Since the IC
internally operates PWM control, it can always produce constant
Operating Principles




See the following page for the electrical circuit diagram.
Electrical Circuit Operation Principles
+5 VDC by changing output pulses in spite of diverse input
voltage levels. This operation serves as a constant voltage
control circuit.
+5 V line overvoltage protection circuit:
ZD53 in the circuit monitors the +5 V line for overcurrent. In case
the voltage rises to 7 V for reasons such as a defective board,
the circuit shuts the Q1 gate in the same process as the +42 V
line overvoltage protection circuit follows.
Voltage drop delay circuit at power off
The C265 PSB/PSE board uses the secondary switch that
includes the delay circuit. The delay circuit allows the printer to
complete the power off operation properly even though the
printer is turned off while it is printing.
A normal power off operation by the user is monitored by the
C265 main board. When it detects a power off, the program
immediately starts the power-off sequence, capping the
printheads, and drops the power.
The electrolysis condenser (C84) continues to operate to allow
the printer to execute this proper power off sequence.
Revision C
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