Service Guide 7-19
8719ET/20ET/22ET Source Troubleshooting
8719ES/20ES/22ES Broadband Phase Lock Problems
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:
Press and rotate the front panel knob to
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 Table
7-4. Substitute with the appropriate band.
• 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).
—pin4=−5.2 V
— pin 3 = +15 V
—pin 2 = −15 V
— pin 1= GND
If the voltages are correct, replace the A52 pulse generator.
Table 7-4 First IF Settings
DAC Number Band Approximate
DAC Number
Displayed
Approximate
Source
Frequency On
Counter
Harmonic Oscilloscope
Frequency
Low 4013 0.910 GHz 5 10 MHz
Mid (8722ET/ES Only) 3541 3.610 GHz 26 10 MHz
High 4004 4.690 GHz 26 10 MHz
High (8722ET/ES Only) 2529 20.17 GHz 112 10 MHz
Preset
Preset
System
180
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