Agilent Technologies 856290216 Divider and Integrator Troubleshooting, Synthesizer l-35

Table 11-12. Divider and Integrator Troubleshooting

Measured VCO

Frequency Relative

to Expected Value

Measured > expected Measured < expected

TP6 Frequency

zero	<2.5 MHz	2.5 MHz		>2.5 MHz
Dividers	Dividers	Dividers	Det	or integrator
Both	Det or integrator	Dividers		Dividers

10.Divider troubleshooting:

a.Check the frequency at A14TP2. It should be equal to the frequency at A14TPl divided by two.

b.The signal at A14TP3 should be above -14 dBm.

c.Use an analog oscilloscope to view the signal at A14TP5. Adjust the scope triggering to view the divide-by-16 signal. The frequency at this point will be varying as the prescaler changes its divide number to either 16, 17, 20, or 21. The prescaler uses 16 as the divide number most frequently. The frequency displayed on the oscilloscope should equal the frequency from TP2 divided by 16.

d.Use an oscilloscope to view the signal at pin 8 of U112. Its average frequency should be given by:

f = f(A14TP5) x 80 MHz/RAW OSC FREQ

where: f(A14TP5) is the frequency measured at TP5, and RAW OSC FREQ comes from step 4.

If the frequency is in error, the fractional divider, block AS, is not functioning. Check that FRAC N RUN on U113 pin 39 is high.

e. Use an oscilloscope to verify that the signals at N-in (U112 pin 8) and N-out (TP6) are identical except for a sub-microsecond delay.

11.Detector and integrator troubleshooting:

a.Check the phase detector output on TPll in block AO. If F-ref is higher in frequency than TP6 (reclocked VCO/N), then the average voltage at TPll should be positive by 0.05 V to 10 V. If F-ref is lower, TPll should be -0.05 V to -10 V.

b.The polarity of the output of the loop gain (block AP, TP12) should be the same as the polarity of the input (TPll). The integrator op amp (U106) output (TP13) should try to go very positive (about +12 V) if its average input (TP12) is positive. If its average input is negative, it should try to go very negative (about -12 V). If its average input is zero and it is functioning correctly, it may take on any output voltage between -12 V and +12 V.

Synthesizer Section 1l-35