Agilent Technologies HP 8719D Service Manual page 338

The A20 backlight inverter assembly supplies the ac voltage for the backlight
tube in the A18 display assembly. This assembly takes the +5.16Vdc from the
Al mother board and converts it to approximately 380 Vat with 5 ma of current
at 40 kHz. There are two control lines:
Digital ON/OFF
n
Analog Brightness
n
Rear Panel
The Al6 rear panel includes the following interfaces:
TEST SET I/O
operate duplexer test adapters.
EXT REF.
This allows for a frequency reference signal input that can phase
lock the analyzer to an external frequency standard for increased frequency
accuracy.
The analyzer automatically enables the external frequency reference feature
when a signal is connected to this input. When the signal is removed, the
analyzer automatically switches back to its internal frequency reference.
10 MHZ PRECISION REFERENCE. (Option lD5)
to the EXT REF (described above) to improve the frequency accuracy of the
analyzer.
AUX
INPUT. This allows for a dc or ac voltage input from an external signal
source, such as a detector or function generator, which you can then measure,
using the S-parameter menu. (You can also use this connector as an analog
output in service routines.)
EXT
AM. This allows for an external analog signal input that is applied to the
ALC circuitry of the analyzer's source. This input analog signal amplitude
modulates the RF output signal.
EXT TlUG. This allows
be set to external through softkey functions.
connection of an external negative-going
This output is connected
Theory of Operation
12-11