Table 1 I-1 1. Unlocked Fractional N Troubleshooting Areas

Measured VCO

 

 

 

Tune Voltage

 

 

 

 

Frequency

Relative

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

to Expected Value

 

 

 

 

 

 

 

 

 

 

 

 

Below -4 V

*“..:‘”

About +ll V

Above +12.5 V

 

 

 

 

 

 

 

 

 

 

 

 

Measured

>

expected

VCO clamp

 

vco

 

Divider or

 

Divider or

VCO

clamp

 

 

 

 

 

 

 

integrator

 

integrator

 

 

Measured

<

expected

VCO clamp

 

Divider or

 

Divider or

 

v c o

VCO

clamp

 

 

 

 

 

integrator

 

integrator

 

 

 

 

Measured,

not

VCO clamp

 

v c o

 

v c o

 

vco

VCO

clamp

oscillating

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

7.VCO clamp troubleshooting:

Q131, Q132 and the associated components should limit the tune voltage at R240 to about fll V. If the integrator (its output voltage is on TP13) tries to produce a voltage outside this range, excess current is shunted through CR131 and Q131 for positive excursions or CR132 and Q132 for negative excursions. The bases of these transistors should be at about f9.6 V for proper operation.

8.VCO troubleshooting:

Check the dc biases in the VCO function block. The bias voltages, for some points in the VCO, are indicated in Figure 11-8.

9.Divider and integrator troubleshooting:

Measure the frequency of the pulses at TP6 in block AO. Look up the expected problem area in Table 11-12 and go to the appropriate troubleshooting steps.

Synthesizer Section 11-33

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Agilent Technologies 856290216 service manual Vco, 1 1. Unlocked Fractional N Troubleshooting Areas