TM 11-7025-210-23
CHAPTER 2
TECHNICAL PRINCIPLES OF OPERATION
2-1. GENERAL
This chapter tells how the line printer works.
The information will help you perform troubleshooting and corrective
maintenance procedures.
2-2. FUNCTIONAL DESCRIPTION
The line printer is an electromechanical device whose major components are a printing mechanism, logic circuitry, control
circuitry and a power supply. Interaction of major components is illustrated in figure 2-1.
2-3. PRINTING MECHANISM
The printing mechanism consists of the main drive, the ribbon drive mechanism, the hammer and print belt assembly, and
the components used in paper handling.
a. Main Drive. The ac motor under the LPS board provides the drive power (fig. 2-2) for the line printer. It
drives the jackshaft, which drives the line feed clutch, the hammer and print belt assembly, and the ribbon drive
mechanism.
b. Ribbon Drive Mechanism. The left print belt pully shaft drives the ribbon drive mechanism (fig. 2-3) through
a series of reduction gears. The ribbon drive mechanism uses a clutch on the bottom end of its drive shaft to ensure only
counter-clockwise movement of the shaft. A drive coupling on the top end of the drive shaft engages a hub in the ribbon
cartridge. The hub is designed to break if the ribbon hangs up or jams.
c. Hammer and Print Belt Assembly. The line printer uses a flexible print belt (fig. 2-4) to carry the type fingers
used for printing. The fingers are mounted in vertical slots in the belt. Each finger has a type character or symbol on the
upper end. There are 3 sets of 64 characters in the print belt. Each set of characters has one special index finger which
contains a marker at the bottom end. The position of each character in the print belt is relative to this special wide index
finger which is detected by a photoelectric light beam. This wide index finger triggers an electronic counting circuit which
counts the finger movement of the belt. As the fingers in the belt move past each possible print column position, the
column position is compared with the stored input data to determine when the finger is in the correct position and the
appropriate hammer is fired. There is a hammer in each print position, for a total of 132 hammers.
(1) The ac motor drives the print belt by means of the jackshaft and the left belt-drive system (fig. 2-5). The
print belt travels counter-clockwise at a constant rate in front of the paper and platen. The inking ribbon passes between
the type fingers and the paper. Printing takes place when a type finger is driven by a hammer against the ribbon and
paper.
2-1
