Front Panel Group; A3 Front Panel Interface Board - Keysight N9912A Service Manual

RF Analyzer
N9912A

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.
Microcontroller and CPLD
The Microcontroller and CPLD sense the keypad keys and the RPG (rotary pulse generator) knob on the front
panel. The 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
Microcontoller.
Front Panel LED's 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.
Real Time Clock Battery
The battery for the RTC (real time clock) on the A6 SOM board is located on the A3 front panel interface
board and is connected to the A6 SOM board via the A5 system board.
Backlight Power
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.
Speaker and Headphones
The speaker is located on the A3 front panel interface board. Left and right audio signals from the A6 SOM
board go to the headphone jack on the A5 system board. These signals are then combined (on the A5
system board) to create a single mono signal for the speaker. An amplifier on the A3 front panel interface
board drives the speaker. Plugging in the headphones disables the speaker output.
Digital Power Supplies
Digital power supplies on the A3 front panel interface board are driven by the Unreg DC voltage from the A5
Service Guide N9912-90003
Theory of Operation
Front Panel Group
5-5