Tektronix TekRanger 2 TFS3031, Руководство по обслуживанию, Страница: 132 / 272

Theory of Operation
TFS3031 TekRanger/TekRanger 2 Service Manual
2–3
The microprocessor on the power-supply board decodes key presses on the
keypad and sends the key-press information to the main board.
The power-supply board receives commands from the main board and power
switch to enable or disable power to the SMDAS board, MMDAS board, main
board, and LCD backlight.
The LCD bias voltage, which controls LCD contrast, is generated on the
power-supply board. The power-supply board receives LCD contrast commands
from the main board, adjusts for temperature variations, and provides the correct
positive bias voltage to the main board to pass on to the LCD.
For instruments with serial numbers B030000 and above, the main board inverts
and scales the positive LCD bias voltage supplied by the power-supply board to
generate a negative LCD bias (contrast) for the LCD.
The main board is the link to the user. It interprets user keypad and external
keyboard presses and sends commands to the SMDAS, MMDAS, and power-
supply boards to acquire data and control LCD backlight and LCD contrast. It
receives data from the SMDAS, MMDAS, and power-supply boards, performs
event analysis, and provides data to the user through the LCD, the serial port,
and the parallel port.
The main board stores and recalls waveform and system data using the floppy
disk drive and internal memory. The main board contains the real-time clock and
the main system software. Time, data, and configuration information needs to be
reprogrammed if this board is replaced. The main board controls downloading of
new system software. This board performs power-on diagnostics to detect errors,
to decide which options are installed, and to decide what capabilities the
instrument has.
The main board contains calibration constants for the SMDAS and MMDAS
boards. Therefore a software calibration command must be performed if the main
board, SMDAS, or MMDAS board is replaced.
For instruments with serial numbers B030000 and above, the main board inverts
and scales the positive LCD bias voltage supplied by the power-supply board to
generate a negative LCD bias (contrast) for the LCD.
Power for the LCD backlight comes from the power-supply board and is
converted to the appropriate high voltage by the LCD backlight power-inverter
board.
Main Board
LCD Backlight
Power-Inverter Board