Agilent Technologies HP 8719D Service Manual page 234

4. Vary the fractional-N frequency from 120 MHz to 242 MHz.
If the period of the signal does not vary from 7.5 psec to 15.5 psec, replace
n
If the period does vary as prescribed, remove the jumper and reinsert A14.
n
1. Place Al3 on the extender board and reconnect all of the flexible cables (the
one to A14Jl is optional).
2. The Al4 assembly generates a TTL cycle start (CST) signal every 10
microseconds when the VCO is oscillating.
3. Connect an oscilloscope to A14TP3 (CR'). (Suggested vertical scale:
Press @iEKE] TIEGGEB~ HEI& #8XI! to stop the sweep. This will make
triggering on these waveforms easier.
5. If there is no signal, replace A14.
6.
Use the CST signal as an external trigger for the oscilloscope and observe the
signals listed in Figure 7-5. Since these 'ITL signals are generated by Al4 to
control A13, check them at Al3 first.
The signals should look simiIar to the waveforms in Figure 7-5.