Welch Allyn PROPAQ CS - Manual (Page 125)

Service Manual Technical overview 121
Expansion Module and printer description
The printer shares battery power with the monitor, but contains its own power supply.
The printer processor communicates with the monitor's processor through the expansion
connector and cable.
The Expansion Module is designed to house the monitor Printer and other circuit boards
for additional parameters. The main circuit board in the Printer is the Printer Main Board.
An additional circuit board (key panel) in the expansion module with printer front chassis
contains the push buttons.
The Printer Main Board is attached to the thermal printer mechanism and should be
replaced as a unit with the printer mechanism if repair is needed.
The Printer Main Board connects to the expansion connector, the battery pack, the push
buttons on the expansion module front panel, the printer mechanism (motor and print
head), and the paper out and head up sensors.
The printer’s microprocessor receives print data and control information from the monitor
and sends data to the monitor. Communication between the two systems (monitor and
printer CPUs) is done by sending and receiving data packets over serial communication
lines.
The print head assembly contains 5 segments consisting of 64 thermal printing dots each
for a total of 320 dots, which cover the width of the paper. As the paper moves under the
print head, the system enables each segment energizing the thermal dots as necessary.
The Printer Main Board consists of five functional blocks: Printer CPU, Printer Driver,
Printer Logic, System Power, and Printer Power. These blocks are interconnected by
several control lines and buses. External to the Printer Main Board are the key panel,
housed in the expansion module front chassis, and the printer motor and print head, both
parts of the printer mechanism.
The Printer CPU block receives data and control information from the monitor through the
Printer Logic block. The Printer CPU sends data to other printer circuits to control printer
functions and sense printer conditions.
Through the Printer Driver the CPU controls the stepper motor and detects when the
paper has run out.
The CPU loads print data into the Printer Logic block and, through this block, controls the
individual printhead segments. The CPU also interfaces with the monitor through this
circuitry.
The System Power block provides several dc power supplies to the printer.
The Printer Power block provides the +24V printer power supply.