HP 8560A, Service Manual

Page: 385 / 450

14. Measure the loop-IF signal at the input to the IF Amp./Limiter (function block AK):
pin 2 20 MHz (approximately
-6
15. Confirm the presence of a 20 MHz square-wave signal at TP405. The square wave should
go from V to V.
16. Set HP 8560A to the following settings:
CENTER FREQ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369.3 MHz
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
17. Use an oscilloscope to confirm the presence of a 2.5 MHz TTL-level signal at TP406.
18. Confirm the presence of a 2.5 MHz TTL-level signal at TP407.
19. Force the loop’s phase/frequency detector to a lock condition by unsoldering one end
of R436. Resistor R436 is located at the base of in function block AK of Al5 RF
Schematic (sheet 3 of 3). This opens the path between the Sampling Oscillator and the
phase/frequency detector.
20. If the dc power supply is connected to pin 16, disconnect the power supply.
21. Connect to This forces both phase/frequency detector inputs to
the same 2.5 MHz signal.
22. Observe the phase/frequency detector outputs, pins 5 and 8, with an oscilloscope.
Narrow TTL pulses should be present. Pin 5 is normally low, pulsing high, and pin 8 is
normally high, pulsing low.
23. Check the cathode of CR401 with an oscilloscope. With the oscilloscope’s input
ac-coupled, a sawtooth waveform approximately 5 should be present.
24. Short C441 with a wire jumper. This changes loop integrator into a voltage follower.
Refer to function block AB of Al5 RF Schematic (sheet 3 of 3).
25. The voltage at pin 15 should measure Vdc. Adjust PHASE DET
BIAS if necessary for Vdc.
26. If the voltage at pin 2 is not Vdc, suspect
27. Check the voltages at the following points:
pin 6
pin 16
Vdc (approximately)
Vdc (approximately)
28. Remove the jumpers.
Synthesizer Section