Service manual

REV.-A
2.1 Printer Mechanism Operation
This section describes the printer mechanism of the FX-870/l 170 printer and explains how the printer works.
The
FX-870/l 170 printer mechanism features a 9-pin impact dot printhead for seriaI Printin9. It has four main
parts: 1) the
printhead mechanism, 2) the carriage movement mechanism, 3) the paper feed mechanism, and
4) the ribbon advance mechanism. Each of these is described below.
2.1.1 Printhead Mechanism
The printhead mechanism consists of the printhead itself, the ink ribbon, and the platen. The printhead contains
a column of 9 wires. Each of these wires has a drive coil which causes the wire to move in and out of the
printhead to print each dot. The four steps below describe how these driving wires work.
(1) The control circuit outputs drive signals to the printhead drive circuit. This changes the printhead drive
voltage, and current flows through the corresponding printhead coil. The coil acts as a solenoid and
generates a magnetic force.
(2)
Thisinducedforce causesthe plate toapproach the coil rod andtheassociated dotwire is rapidly ejected
to impact on the platen.
(3) The dot wire presses the ink ribbon up against the paper as it hits the platen and in this way prints a dot
on the paper.
(4 As soon as the current through the coil is switched off, the force induced in the coil rod stops. The plate
then returns to its original position (the position assumed before the coil was energized) through the
action of the plate spring. After the dot wire hits the platen, the rebounding force of hitting the platen works
with the wire resetting spring to pull the wire back to its original position.
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