Agilent Technologies FieldFox MW N9913A, Service Manual

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N9927-90003 5-5
FieldFox Analyzer Theory of Operation
Front Panel Group
Front Panel Group
The front panel group consists of the following assemblies:
• A3 Front Panel Interface Board
• A2 LCD Assembly
Refer to Figure 5-1 for a simplified overall block diagram which includes the front panel group.
A3 Front Panel Interface Board
The main function of the A3 Front Panel Interface board is to support the user interface but it also
contains the digital power supplies.
USB Microcontroller
The USB Microcontroller senses the keypad keys and the RPG (rotary pulse generator) knob on the front
panel. The USB Microcontroller communicates with the A5 System board via a USB interface.
There is no separate ID EPROM on the A3 Front Panel Interface board. All ID information is stored in
the USB Microcontoller.
Keypad Lights and ON/OFF Button
The power for the keypad LED's generated on the A3 Front Panel Interface board is derived from the
+5 V digital supply. The keypad LED's are turned on for a few seconds following each key press. This
function is controlled by the firmware on the A6 SOM board.
The On/Off LED is controlled by a signal from the A5 System board. The connections for the On/Off
Button and LED are direct to the A5 System board.
LCD Backlight
Power for the backlight on the A2 LCD assembly is generated on the A3 Front Panel Interface board.
Digital 5 volts is converted to approximately 25 volts. The actual voltage determines the brightness of
the backlight. Two control lines from the A5 System board control on/off and intensity functions. These
control lines are driven by the system monitor microcontroller on the A5 System board.
Battery Charger and Manager
This circuitry controls charging of the battery based on a battery charger IC. This IC is powered by a
digital output on the System Monitor. The System Monitor has the capability to reset the IC, if required,
by recycling the power to the IC.
This circuitry also controls the source of the Unreg DC: Batt or Ext DC. It reads the battery pack
information via the Smart Batt Bus. Batt Neg is connected to the A5 ground plane.
There is an input inrush current control circuit on the Ext DC input that limits inrush current to 4 amps.
Variable Voltage Source
This circuitry provides a constant voltage intended to bias circuits under test.
The user interface for controlling this function may be accessed via System > System Configuration .