Publication Number 53719. Issue 3, April 2012
Page 12
SERVICE MANUAL FOR THE 13754 TGX150 INTERNAL RLAN TYPE A/B SC ETM
•
The Control Board
The control board is a surface mounted printed circuit board that controls all
the functions governed by the ETM's software, such as the display, keyboard
and the infra-red module. To do this, it is linked to the other parts of the
system by a number of connectors, as follows: -
PLEXT1
-
Keyboard and Display data
PLEXT2
Keyboard and Display Power
PLA
-
Main input
PLJ
-
Paper low sensor
PLM
-
Printer data
PLO
-
Paper out microswitch
PLP
-
Serial number board
PLT
-
Printer stepper motor
PLX1
-
Memory Expansion & Internal Serial PCB
PLY1
-
Memory Expansion & Internal Serial PCB
SOL1
-
Module housing solenoid
As well as providing the "control" of the various circuits in the ETM, the
control board includes the switch mode power supply circuits to generate the
necessary 5V supply to all the logic circuits throughout the ETM's electronics.
The board generates the 12V required for the infra-red electronics and the 24V
switched for the thermal printer. The board also provides an RS485 output for
interfacing with Internal GPS. The various voltages are generated from the
24V input to the board at the main input socket (PLA), which is a component
of the control board. In the event of a power failure the rechargeable lithium
backup battery (marked BT1 on the control board) maintains power to the real
time clock and memory components.
A 3A polyswitch fuse protects the input supply to the circuit board.
The microprocessor is an Intel 386EX 132-pin device with a clock speed of
66MHz. The timing crystal provides the appropriate timing pulses to regulate
the device.
•
Keyboard PCB
The keyboard PCB is a component of the keyboard and display assembly and
is mounted on the back of that assembly. The board consists of a series of
LED’s to provide key illumination and a switch matrix that consists of tracking
shaped in concentric circles that are shorted together when the actual switch
button is pressed. A buzzer is also mounted on the board, although its
actuating circuitry is located on the control board. The keyboard is connected
to the control board via PLEXT1 on the control board.
The display is a non-repairable item whose electronics are supplied as an
integral part of the display assembly.
