Pulse Generator (A52) Check With Oscilloscope - Agilent Technologies 8719ET Service Manual

8719ET/20ET/22ET
8719ES/20ES/22ES
RF Network Analyzers

Pulse Generator (A52) Check with Oscilloscope

1. Monitor the 1st IF signal at the output of A65 A sampler assembly: disconnect the SMB
cable from A65 and connect an oscilloscope to the sampler assembly IF output. Connect
a frequency counter to PORT 1. Then perform these steps:
a. To set the fractional-N VCO to 180 MHz, press the following:
Preset PRESET: FACTORY
SERVICE MENU
System
FRACN TUNE ON
Press
SRC ADJUST MENU
change the DAC number to about 4013. Readjust the DAC number as required to measure
an output frequency of about 0.91 GHz.
NOTE The frequency counter may have to be removed from PORT 1 to provide
enough of a reflection to see signal on the scope.
2. Now the oscilloscope should display the IF signal as a sine wave of about 10 MHz. The
actual frequency can be expressed as this equation:
Oscilloscope frequency = (counter frequency) − (180 MHz) × (harmonic)
3. Repeat steps 1b and 2 using the information in the second through fourth rows of
7-4. Substitute
DAC NUM LOW BAND
Table 7-4 First IF Settings
DAC Number Band
Low
Mid (8722ET/ES Only)
High
High (8722ET/ES Only)
• If the IF signals are correct, replace the A11.
• If the IF signals are incorrect, check the pulse generator bias voltages at the
motherboard (A17J19).
— pin 4 = −5.2 V
— pin 3 = +15 V
— pin 2 = −15 V
— pin 1= GND
If the voltages are correct, replace the A52 pulse generator.
Service Guide
Preset
SERVICE MODES
180 M/µ
DAC NUM LOW BAND
with the appropriate band.
Approximate
DAC Number
Displayed
4013
3541
4004
2529
Broadband Phase Lock Problems
and rotate the front panel knob to
Approximate Harmonic
Source
Frequency On
Counter
0.910 GHz 5
3.610 GHz 26
4.690 GHz 26
20.17 GHz 112
Source Troubleshooting
Table
Oscilloscope
Frequency
10 MHz
10 MHz
10 MHz
10 MHz
7- 19