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Theory of Operation
This Service Guide supports troubleshooting the Agilent Technologies 54835A/45A to
assembly level. Theory of operation is included only as supplemental information. It is
not comprehensive enough for component-level troubleshooting.
Block-Level Theory
The Agilent Technologies 54835A Oscilloscope has four channels which are individually sampled
at 2 GSa/s. Each channel is stored into 32 Kbytes of memory. Pairs of channels can be combined
to sample at 4 GSa/s and extend memory to 64 Kbytes.
The Agilent Technologies 54845A Oscilloscope has four channels which are individually sampled
at 4 GSa/s. Each channel is stored into 32 Kbytes of memory. Pairs of channels can be combined
to sample at 8 GSa/s and extend memory to 64 Kbytes.
The front panel provides:
• Dedicated knobs and pushbuttons for major oscilloscope functions.
• An 8.4-inch (diagonal) color flat panel display for waveform, measurement, and graphical
interface display.
• A 3 1/2-inch flexible disk drive.
• BNC connectors for channel input signals, auxiliary trigger input, and auxiliary output.
• AutoProbe interface for probe power and probe control.
• A connection for probe compensation.
The rear panel provides several connections:
• The line power input.
• An GPIB connector, for connection to an instrument controller.
• An RS-232 connection.
• A parallel printer connection.
• VGA monitor connection.
• Mouse and keyboard connections.
The instrument has several assemblies and four attenuators. Use the instrument block diagram
on the previous page for the following discussion.
Power Supply Assembly
The switching power supply provides 300 W maximum for the instrument. The ac input to the
power supply is 100–240 Vac, +/-10%. Maximum input power is 390W. The ac input frequency
is 47 to 440 Hz.
Filtered voltages of +5.1 V, –5.2 V, +12.2 V, and –12.2 V are supplied to the acquisition board,
where they are distributed throughout the board and to other assemblies.
FPD Monitor Assembly
The monitor is a thin film liquid-crystal display (TFT-LCD). This FPD is an 8.4-inch diagonal,
640 by 480 pixel VGA Color Monitor. The assembly requires
+3.3 V and +12 V from the power
supply.
A twin fluorescent back light provides illumination for the LCD. The Backlight Inverter assembly
converts the +12 V to +300-1000 volts (acrms) and drives the back light.