Agilent Technologies 8564EC, Service Manual

Page: 425 / 512

Chapter 11 557
Synthesizer Section
Unlocked YTO PLL
31.As the signal generator frequency is increased to 76 MHz, the
voltage at A14J17 pin 1 should change from approxi12 V to
−
12 V.
32.Set the signal generator to the following settings and repeat step 30.
Frequency .................................................................. 56 MHz
Amplitude ................................................................
−
15 dBm
33.If the voltage monitored in step 30 is correct with a 0 dBm output
but not with
−
15 dBm output, suspect the limiting amplifier function
block AE.
34.Place A14J23 jumper in the NORMAL position and reconnect W32
to A14J501.
Check YTO FM
coil driver and
main loop error
voltage driver
(steps 35-40)
35.To troubleshoot the YTO FM coil driver, refer to step 6 of "1st LO
Span Problems (2.01 MHz to 20 MHz)."
36.Steps 36 through 40 verify that the YTO-loop error voltage is
reaching the FM coil. The main loop error voltage driver has a gain
of either 1.5 or 15; the analyzer firmware controls the gain during
the locking process. The error voltage is read by the ADC on the A3
interface assembly. U324D calibrates out any offsets from true
ground. A14U326A inverts the sense of the YTO loop to lock the
YTO on lower sampler-sidebands (YTO frequency (sampler
frequency
×
sampler harmonic)). The fractional N frequency
indicated in the FREQ DIAGNOSE menu will be negative when
locking to lower sidebands. Refer to function blocks E, M, and N of
A14 frequency control schematic (sheet 2 of 5) in the 8560 E-Series
Spectrum Analyzer Component Level Information binder.
Set the spectrum analyzer to the following settings:
Center frequency ..................................................... 300 MHz
Span ................................................................................. 0 Hz
37.Remove A14J23 jumper and connect a dc power supply to A14J23
pin 2. Connect ground to A14J23 pin 3. Set the dc power supply to
+7.5 Vdc.
38.Verify the nominal test-point voltages listed in Table 11-6 on page
558 .
39.Change the input voltage to
−
7.5 volts and re-verify that the voltages
listed in Table 11-6 on page 558 are the same except for a change in
polarity.