Agilent Technologies HP 8719D Service Manual page 294

19. (Ground reference)
Gnd
20. Al2 (Ground reference)
21. FN VCO
This node displays the Al4 F'N VCO tuning voltage. This voltage comes
from the Al3 fractional-N (analog) assembly and is the return path for
the fractional-N phase-locked loop. If the Al3 and Al4 assemblies are
functioning properly and the VCO is phase locked, the trace should look like
the trace shown in Figure 10-S when in Log F'req. sweep mode. Any other
waveform indicates that the F'N VCO is not phase locked. The vertical lines
in the trace indicate the band crossings. (The counter can also be enabled to
count the VCO frequency. Use CW mode.)
Figure 10-9. Node 21: FN VC0 Tun, FN VC0 Tuning Voltage
22. (Ground reference)
23.
This node checks the analog bus counter gate signal. You should see a
flat line at +5V. The counter gate activity occurs during bandswitches,
and therefore is not visible on the analog bus. 'Ib view the bandswitch
counter gate)
Service Key Menus and Error Messages