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

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