Theory of Operation
Power Supply
The main p ower supply module for the TDS2000C series oscilloscopes is a
wide input range universal supply. It can provide about 25 W of power for the
oscilloscop
e, while allowing the input to run from about 90 V to 264 V. Input
frequency ranges from 47 Hz to 440 Hz, which allows operation in virtually all
countries in the world and in several off-grid environments, such as power on
military aircraft.
The secondary supplies from the power supply and the approximate current draws
are listed in a table with the associated connector pins on J101. (See Table 6-5.)
The P2 connector uses 4 positions and 3 wires, which are +6 V, +3.3 V, and GND.
For information on voltages used in the oscilloscope, refer to the Troubleshooting
section of this manual.
Display Module
The color display module is a standard passive liquid crystal display (LCD).
The unit is patterned with 320 columns x 3 sub-columns by 240 rows and has
the associated drivers and backlight. The LED backlight output is about 75 mA
at 15.5 V.
Front Panel
Two-Channel
Oscilloscopes
You can manipulate all of the switches, and position encoders on the Front-Panel
board of 2-channel oscilloscopes. Several LEDs are used to indicate when the
Multipurpose knob is active, when Autorange is active, and when a Save action
is in progress. For more information on the LEDs, ref
er to the User Manual for
your oscilloscope.
An IC on the Front-Panel board provides buffering and multiplexing of switch
signals to the Main board. Two signals and a sense line are provided by the Main
board to support the front panel. One of these lines resets the scan; a second line
clocks the scan to the next position; and the sense line receives the current state of
the selected switch or encoder position.
For the encoders, some amount of debouncing occurs inside the front-panel IC.
All key debouncing is handled in the display ASIC on the Main board.
The LEDs are controlled by latching the value of the Channel 1 - 2 front-panel
scan counter when the appropriate scan value is set.
Four-Channel
Oscilloscopes
The Front-Panel board of the 4-channel units is effectively two panels in parallel.
The left side of the board is largely handled by the display ASIC for channels
1 and 2. The right side of the board is handled by the channel 3 and 4 ASIC.
Separate front-panel ICs support these data paths.
3–6 TDS2000C Series Oscilloscope Service Manual
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