Tektronix TDS1001C-EDU, Service Manual

Page: 38 / 114

Theory of Operation
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, refer to the user manual for
your product.
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 FPGA 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 FPGA 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.
26 TDS2000C and TDS1000C-EDU Series Oscilloscope Service Manual