B102 Main Board - Epson STYLUS Scan 2500 Service Manual

EPSON Stylus Scan 2500
1. As long as the AC power cable is plugged into a power source, voltage
flows through the primary side (bottom in figure above) of the power
supply board.
2. The fuse prevents damage to the power supply board in case the current
is too strong.
3. The filter circuit acts to filter incoming electrical noise and to smoothen
the electrical current.
4. The full wave rectifier circuit converts AC to DC.
5. The smoothing circuit stabilizes out the DC wave.
6. The main switching circuit controls the flow of current to the transformer
(hence to the entire secondary side). The main switching circuit,
transformer, and feedback circuit work in combination like the heart,
lungs, and brain (respectively) of the human body. The main switching
circuit is the variable-flow generator like the heart, the transformer
convert the power to a usable form like lungs adding oxygen to blood,
and the feedback circuit controls the flow like the brain controlling the
heartbeat/pulse.
7. The transformer receives approximate 100V or 220V DC (depending on
the model) and steps the voltage down before sending it to the secondary
side.
8. The current is stabilized as it goes through another smoothing circuit.
9. The 24V, 12V, 5V, and 3.3V regulators control the flow of current so that
only the rated voltage flows through each regulator. The input level
fluctuates but the output is constant.
10. The 42V, 24V, 12V, 5V, and 3.3V line over-voltage limitation protectors
monitor their individual lines for any voltage over the rated amount. If
over-current is detected, a signal is sent to the photo coupler to decrease
current.
11. The +42V line constant control is similar to a regulator in that it is always
working, but instead of fixing the over-current, it reports the over-current
to the photo coupler.
12. The photo coupler is one part of the over-current feedback system. A
photo coupler is necessary because electrical current cannot cross the
from the primary side to the secondary side and vice-versa; the absolute
Operating Principles
ground levels for the primary side (AC as well as DC) and secondary side
(DC only) are different, so they will short if they come into contact. The
photo coupler transmits signals via a photo emitter.
13. The feedback circuit 1) receives over-current information from the photo
coupler by means of a photo receiver 2) monitors the transformer for
over-current and 3) receives power-supply information/commands from
the MAIN board and power switch. The feedback circuit changes the
voltage sent from the main switching circuit to the transformer when
necessary.
14. The power-drop delay circuit is a thirty-second timer that activates
whenever the power is turned off. The thirty-second period is necessary
to guarantee safe completion of the power-down sequence.

2.5.2 B102 MAIN Board

The B102 MAIN Board controls the printer, scanner, copy function, pumping,
paper feeding, and all signals to/from the control panel unit. The following
figure shows the MAIN Board circuit diagram for EPSON Stylus Scan 2500.
Electrical Circuit Operating Principles
Revision A
57