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

REV.-A

2.2 POWER SUPPLY OPERATION

The printer can be powered by either of two power supply boards: the 120 V CO60 PSB board or the
ways in which they supply power to the printer are identical. These power supply boards output the
DC current necessary to drive the printer control circuits and the printer drive mechanism. Table 2-3
shows the input voltages and fuse ratings for these boards.

2.2.1 Power Supply Overview

The power supply board has two power output lines that supply power to the various control circuits
and drive mechanisms. Table 2-4 lists the parts of the printer that run off these two DC output supply
voltages.
Table 2-4. Power Supply Output Voltages and Applications

2.2.2 Supply Circuit Operation

Figure 2-l 6 shows the power supply circuitry in block diagram form. AC power feeds into the printer
from the external power source. A filter circuit removes the noise. The AC voltage then undergoes full
wave rectification and is smoothed to produce the direct current supply voltage. This voltage is fed
through a switching circuit and secondary smoothing circuit to produce the stepped down +35 VDC
supply. A +35 V line voltage detector circuit is connected to the switching circuit. This feedback control
arrangement ensures that the +35 VDC supply remains stable.
The +5 VDC supply is achieved by feeding the +35 VDC line through the +5 VDC power supply circuit.
This circuit further steps down the +35 VDC voltage and outputs a stabilized +5 VDC supply.
There are four circuits to protect the supply circuitry and avoid danger. The +5 VDC line contains a
current overload protection circuit and a voltage overload protection circuit. The current overload
protection circuit is part of the + 5 VDC supply circuit. It cuts the + 5 VDC line if the current is too great.
The + 5 V voltage overload protection circuit cuts the supply if the voltage reaches or exceeds + 7 VDC.
It stops switching circuit operation, which stops the output of the +35 VDC line.
Table 2-3. Power Supply Boards
Input Voltage WAC)
Board
CO60 PSB
CO60
PSE
Output Supply Voltage (DC)
v
v
Fuse Fl Rating
103.5
to 132
198 to 264
Applications
Carriage motor drive
Paper advance motor drive
Printhead drive
CO60
MAIN board logic circuitry
Various sensors
Control panel LEDs
Paper advance
2 - 1 2
motor hold