Electrical Circuits; Power Supply Board - Epson Stylus Photo 870 Service Manual

EPSON Stylus Photo 870/1270

2.4 Electrical Circuits

The electrical circuits of the EPSON Stylus Photo 870/1270 are
composed of the following boards.
! Main board:

! Power supply board:

! Panel board:
Figure 2-13 shows the major connections of the three boards and their
functions.
C 2 9 8 P N L B o a r d ( S C 8 6 0 )
C304 PNL Board
C 3 0 4 P N L B o a r d ( S C 1 1 6 0 )
C 2 9 8 M A I N B o a r d
3 . 3 V R e g u l a t o r
P o w e r o f f + 5 V D C + 4 2 V D C
C 2 9 8 P S B / P S E
B o a r d
Figure 2-13. Electrical Circuit
C304MAIN
C298PSB/PSE
C304PNL
P r i n t e r M e c h a n i s m
C R M o t o r
P . M o t o r
A S . / P u m p M o t o r
H e a d D r i v e r B o a r d
S e v e r a l S e n s o r s
2.4.1 Power Supply Board
The C298PSB/PSE power supply board is used in both the EPSON
Stylus Photo 870 and EPSON Stylus Photo 1270.
The power supply board uses a switching regulator. It converts AC line
voltage into smooth, filtered DC current at two voltage levels:
! 5 VDC for powering the sensors and main logic board
! 42 VDC for powering the printhead, carriage motor, paper feed
motor, and pump/ASF motor
The power supply board incorporates overvoltage protection to detect
any abnormal rise in output voltage caused by a defect in the circuit. If
the 42 volt output rises to 48 volts, or the 5 volt output rises to 9 volts,
the power supply board shuts itself off. Once it's deactivated, it
cannot recover until you turn the printer off and then back on. In case
of a short circuit, the power supply board shuts down the 42 V line
when the voltage level drops to 36 V.
The power supply circuit also includes a voltage drop delay circuit.
When you turn off the printer by pressing the external power button,
the delay circuit keeps the power supply on long enough for the
printer to complete its power-off operations (paper ejection and
printhead capping). After a pre-determined length of time, the power
supply shuts itself off.
To save energy, the power supply board is designed to go into energy-
saving mode when it receives an ESAVE signal from the main board.
Once the circuit is in this mode, it maintains the 42-volt line at
approximately 20 to 23 volts.
"
The external power switch is only a secondary switch in
W A R N I N G
the power supply circuit. The primary side of the power
supply is always "live," even when the printer appears
to be off. Always unplug the printer before servicing.
"
Never touch the heat sink on Q1 (the main switching
transistor) with your bare hands; it is not electrically
insulated.
Chapter 2 Technical Overview
14