HP 8562E, Service Manual

Page: 391 / 482

Check 10 MHz reference to phase/frequency detector (steps 9-14)
9. On the spectrum analyzer, press PANEL , and INT .
10. Check the 10 MHz reference frequency-accuracy by connecting a frequency counter to
and verify that the reference frequency is 10 MHz Hz after a 5 minute
warmup period.
11. If a 10 MHz signal V peak-to-peak is not present at refer to the “10 MHz
Reference” in Chapter 12, “RF Section.”
12. Measure the signal at TP301 with an oscilloscope. Refer to function block M of Al5 RF
schematic.
13. Measure the signal at pin 11 with an oscilloscope. Refer to function block X of Al5
RF schematic. This signal should be TTL levels at 10 MHz with a 60 percent duty cycle.
14. If TTL-level signals (approximately 10 MHz) are not present, check signals backwards
through the loop to find a fault in the signal path.
15. Measure the signals at the following test points with an active probe/spectrum analyzer
combination:
Junction of
and C571
100 MHz,
Junction of R715,
R716, R567, and R568 100 MHz, -3
pin 3 100 MHz,
pin 1 100 MHz,
16. If an approximately 10 MHz TTL signal is present at pin 11 with 60 percent duty
cycle, and the RF portion of the phase-lock loop is functioning, the fault probably lies in
the phase/frequency detector or the 100 MHz lock loop integrator.
Check phase/frequency detector (steps 17-22)
17.
18.
19.
20.
21.
Monitor pin 5 and pin 9 with an oscilloscope. These are the two outputs of
the phase/frequency detector. Refer to function block 0 of Al5 RF schematic.
A locked loop will exhibit stable, narrow (approximately 20 ns wide), and positive-going
TTL pulses occurring at a 10 MHz rate at
pin 5 and pin 9.
If the loop is unlocked, but signals are present on both inputs of the phase/frequency
detector, the output pulses will be superimposed on each other.
If the loop is unlocked, and there is no signal at one of the phase/frequency detector
inputs, one phase detector output will be at TTL low and the other will be at TTL high.
For example, if there is no input signal at
pin 3, pin 5 will be TTL low and
pin 9 will be TTL high. If there is no input signal at pin 11, pin 9 will
be TTL low and pin 5 will be TTL high.
To remove the 10 MHz reference input to the phase/frequency detector, press
PANEL, and with no signal applied to the rear-panel 10 MHz REF
IN/OUT connector.
Synthesizer Section