Power Supply Operation; Power Supply Overview; Power Supply Circuit Operation - Epson FX-870 Service Manual

Power Supply Operation

The FX-870/1170 printer is powered by a 120 VAC power supply board (C076 PSB board assembly).
This board outputs the DC current necessary to drive the printer control circuits and the printer
drive mechanism. Fuse Fl(2.5 A/125 V) is used to protect the power supply circuit of the board
in case of a short circuit.
Table 6-3. Power Supply Input Voltage and Fuse Rating
Input Voltage
103.5 - 132 VAC

Power Supply Overview

The power supply board has two power output lines that supply power to the control circuits and
the drive mechanisms. Table 6-4 lists the components (parts or assemblies) of the printer that are
powered by these two DC voltages.
Table 6-4. Power Supply Output Voltages and Applications

Power Supply Circuit Operation

Figure 6-22 shows the power supply circuitry in block diagram form. When AC power enters the
printer from an external power source, the filter circuit removes the noise. The AC voltage then
undergoes full wave rectification and is smoothed to produce direct current. The voltage is then
fed through the switching circuit and the secondary smoothing circuit to produce a stepped down
control arrangement ensures a stable +35 VDC voltage supply.
A +5 VDC voltage is generated by feeding the +35 VDC voltage through the +5 VDC power supply
circuit, where the +35 VDC is stepped down to a stable +5 VDC voltage. The switching regulator
IC containing the overcurrent/overvoltage control circuits performs this function. It controls the
Epson FX-87011170
Output Voltage (DC)
Fuse Fl Rating
2.5 A/l25 V
Applications
CR (carriage) motor drive
PF (paper feed) motor drive
Printhead drive
Main control board logic circuitry
Sensors
Control panel LEDs
PF (paper feed) motor hold
Principles of Operation
6-19