Scale-Tronix 5002 - Page 26

wiring. This device is self-resetting and will restore
operation once the short is removed.
A charge indicator circuit is provided by LED302 and
current limiting resistor R302. A jumper contained in
the battery wiring (pins 2 and 3) completes the circuit.
The charge indicator is wired in series with the
scale's front panel "CHARGE" annunciator. Note that
if the battery is disconnected from the power supply
board; or the power cable, instrument board, display
cable, or display board are disconnected, the LED302
charge indicator will not light. Note also that the
charge indicator is monitored on some scales to tell
the readout's microcomputer that AC power is present
and thus prevent automatic shut-off (see section
4.24.5, “CHARGE MONITOR CIRCUIT’).
4.50 PRINTER GENERAL
This internal printer employs a thermal type
print mechanism which heats a specially coated
paper to produce the resulting paper ticket. The total
printing system consists of three assemblies:
4.) Mechanical printer assembly with motor and
thermal print head, model EPT-1014LW2 or model
EPT-2014S2L.
2.) Printer interface board assembly, model EPT-
R1002 or model EPT-R2002
3.) Printer controller board assembly, model
23PRTROZ, 23PRTRO3 or 23PRTRO4.
Note: The mechanical printer assemblies and printer
interface board assemblies must match as follows:
printer EPT-1014LW2 uses the EPT-R1002 interface
board; printer EPT-2014S2L uses the EPT-R2002
interface board. The 23PRTRO2, 23PRTRO3, and
23PRTRO4 printer controller board assemblies are
interchangeable.
4.51 MECHANICAL PRINTER ASSEMBLY
The mechanical printer assembly employs a
thermal print head consisting of a vertical row of eight
(8) small resistors, each of which when momentarily
heated produce a small dot on the specially treated
thermal paper. The use of a thermal type of printing
mechanism eliminates the need for ribbons or ink
cartridges and provides quiet, maintenance-free
operation.
A stepper motor positions the head across the paper
as the printing occurs, driving it from the left most
"home" position to the far right. Printing occurs during
this left-to-right sweep of the print head. A total of 144
dot positions (horizontally) are available for printing.
Specific contral of the print head resistors is performed
by the printer interface board which develops all the
necessary timing and synchronization. When the
printing head reaches the far right position (printing of
a line is finished) the stepper motor reverses direction
and returns the print head to the home position.
During this reverse of the print head travel a
mechanical cam assembly engages which
simuttaneousty lifts the print head from its contact with
the paper and advances the paper one line. A switch
located in the printer mechanism closes to indicate
when the print head has finally returned to its home
position,
The printer is supplied as an assembly and has no
serviceable parts.
4.52 PRINTER INTERFACE BOARD
A separate printer interface board is provided
to perform all the timing, synchronization, decoding,
and driving of the printer. The printer interface hoard
can receive the character print information in either
serial or parallel format. In this application the
interface receives the characters to be printed from the
scale's instrument board via a serial interface in
standard ASCII format.
The interface board contains its own microcontroller
with memory, along with the various drivers needed to
support the print head resistors and stepper motor, A
single flex cable connects the printer mechanism to
the interface board.
Operation of the printer interface board is directed by
the internal software of the microcontroller. Various
operating options of the interface board (type of
printer, serial or parallel interface, parity, bits, baud
rate, etc.) are controlled by the position of
programming jumpers. Jumper positions are as
follows:
24 5002, 5102, 5602, 6002, 6102, 6202, 6502, 6702