56 Keysight FieldFox Handheld Analyzers Service Guide
Theory of Operation
Front Panel Group
5-
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.
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