HP 8560E, Service Manual

Page: 550 / 665

Chapter 10 549
Synthesizer Section
Unlocked Fractional N PLL
A15 RF assembly.
3. Change the spectrum analyzer from the fractional N span to 0 Hz.
4. Check the frequency at A14TP1. It should equal the value found by
pressing
CAL
,
MORE 1 OF 2
,
FREQ DIAGNOSE
, and
RAW OSC FREQ
.
5. Check the tune voltage at the ungrounded end of C135.
6. Look up the expected problem area in Table 10-12 on page 549 with
the information from steps 4 and 5. Go to the appropriate
troubleshooting steps.
Table 10-12 Unlocked Fractional N Troubleshooting Areas (08560-60069 and
Above)
Measured VCO
Frequency
Relative to
Expected Value Tune Voltage
Less than
−
4 V
About
−
3.3 V
Between
−
2 V and
+10 V
About
+11 V Greater
than
+12.5 V
Measured >
expected VCO clamp VCO Divider or
integrator Divider or
integrator VCO clamp
Measured <
expected VCO clamp Divider or
integrator
Divider or
integrator VCO VCO clamp
Measured, not
oscillating VCO clamp VCO VCO VCO VCO clamp
Table 10-13 Unlocked Fractional N Troubleshooting Areas (08560-60062 and
below)
Measured VCO
Frequency
Relative to
Expected
Value Tune Voltage
Less
than
−
12.5 V
About
−
11 V
Between
±
10 V
About
+11 V Greater
than +12.5
V
Measured >
expected VCO
clamp VCO Divider or
integrator Divider or
integrator VCO clamp
Measured <
expected VCO
clamp Divider or
integrator Divider or
integrator VCO VCO clamp
Measured, not
oscillating VCO
clamp VCO VCO VCO VCO clamp