Mechanical Operation; Printhead Mechanism And Operation - Ithaca 75 User Manual

AC Switch Plate
The AC Switch Plate mounts the Power Switch, AC Fuse, and AC Noise Filter.
Power Transformer
If the Power Transformer temperature rises abnormally, the transformer's built-
in temperature fuse blows to prevent adverse effects on other components.

MECHANICAL OPERATION

PRINTHEAD MECHANISM AND OPERATION

The Printhead is spring-loaded, using a permanent magnet, and can be easily
removed or installed. The Printhead is mounted on a Carriage that runs parallel
to the Platen and is connected with the control circuit via the Interconnect
Board.
The Printhead consists of the following items:
♦ Wire Guide
♦ Wires
♦ Armature Assembly
♦ Yoke
♦ Springs
♦ Spacer
♦ Magnet Assembly
♦ Thermistor
♦ PC Board
Printhead Operation
When the Printhead is in the non-printing state, each armature is attracted by
the permanent magnet and the springs holding the armatures are compressed by
the thickness of the spacer. Therefore, the print wires, which are fastened to the
individual armatures, are held retracted within the wire guide.
When signals corresponding to a character to be printed are detected by the
control circuit, currents flow through the corresponding coils to nullify the
magnetic flux generated by the permanent magnet assembly. With the magnetic
flux nullified, the print wire coil armatures are driven toward the Platen by the
force of the armature springs. The print wires, fastened to the armatures, are
ejected from the tip of the wire guide and strike the paper through the ribbon.
Appendix B: Theory of Operation
85