HP 8560A, Service Manual

Page: 322 / 450

Low-Pass Filter
Refer to function block AB of A4 Cal Oscillator Schematic Diagram in the
HP Spectrum Analyzer Component Level Information
binder.
1. Connect a DVM positive probe to pin 4.
2. On the spectrum analyzer, press
Press FULL IF ADJUST. Observe the DVM reading between the displayed messages
IF ADJUST STATUS: 300 RBW and IF ADJUST STATUS: 3 RBW. During this time
period, the voltage should be within a 2 to 10 Vdc range.
4. Observe the DVM reading while IF ADJUST STATUS: AMPLITUDE is displayed. The reading
should be within the 2 to 10 Vdc range.
5. If the DVM reading is outside the range in step 3 but inside the range in step 4, suspect
one of the filter reactive components.
Sweep Generator
Refer to function block Z of A4 Cal Oscillator Schematic Diagram in the
HP
Spectrum Analyzer Component Level Information
binder.
A properly operating sweep generator generates a series of negative-going parabolas. Before
the sweep, switches
and turn on, shorting and (the
output is at 0 volts). These switches open to start the sweep. The output of pin 1,
is 0.35 V to 10 V, depending on the sweep width selected by and This
voltage appears across Capacitor integrates the current through
The output of is a straight, negative-going ramp. Capacitor and resistor
integrate the output of which starts a negative ramp at the
beginning of the sweep. The ramp from is added to the current in via
Integrating this ramp results in the parabolic output waveform.
AM/FM Demodulation, Audio Amplifier, and Speaker
Refer to function blocks R, S, and T of A4 Cal Oscillator Schematic (sheet 4 of 4) Diagram in
the
HP Spectrum Analyzer Component Level Information
binder.
If the audio circuits are not functioning use the following procedure to isolate the problem.
1. Set an AM signal generator controls as follows:
Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Amplitude
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -6
Modulation Type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80% AM
Modulation Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 Hz
2. Set the spectrum analyzer controls as follows:
CENTER FREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 MHz
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SWEEP TIME . . . . . . . . . . . . . . . . . . . .
50ms
REF LVL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .0 dBm
RES BW
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
SCALE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..LINEAR
8-40 IF Section