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3. Set the other spectrum analyzer controls as follows:
Span
..........................................................
..5MH
z
Reference level
................................................
-20
dBm
Center frequency
............................................
..10.7MH
z
4. On the HP 85623 spectrum analyzer, set the cal oscillator to 10.7 MHz by selecting
Fixed Tuned to 10.7
MHz
.
5. A -25
dBm
signal from A5J5 should be displayed. If the signal is missing, disconnect W52
(coax 9) from
A5J4.
This is the cal oscillator signal input from the cal oscillator on the A4
assembly.
6. Connect the end of cable W52 to the input of the second spectrum analyzer. The signal
coming from cable W52 should be -35
dBm
at 10.7 MHz. If the cal oscillator signal from
cable W52 is correct, the A5 IF assembly is probably at fault.
Troubleshooting
the
Cal
Oscillator
with
the
TAM
1. Enter the TAM Cal Osc Troubleshooting Mode.
2. On the HP 85623 spectrum analyzer, disconnect cable W52 (coax 9) from A5J4 and
connect this end of cable W52 to the input of a second spectrum analyzer.
3. Set the controls of the second spectrum analyzer connected to cable
W52
to the following:
Span
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..5MHz
Reference level
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -30
dBm
Center frequency
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.7 MHz
4. Select each of the fixed-tuned frequencies. Verify at each frequency that the signal
amplitude measures -35
dBm.
If the frequency is incorrect, do the following:
a. Verify that the reference divider output (A4U811 pin 9) is 100 kHz. If it is not, verify
that the 10 MHz reference is present at A4U811 pin 1.
b. Verify that the frequency found on the output of the divider (A4U808 pin 15) matches
the output of the reference divider. Matching frequencies indicate the oscillator loop is
locked. If the loop is not locked, troubleshoot the divider, oscillator, or phase detector.
c. Verify that the frequency found at the divider input (A4U808 pin 3) matches the CW
frequency chosen in step a. Matching frequencies indicate a properly working oscillator.
If the frequency is different, troubleshoot the divider.
d. Repeat step c for all the CW frequencies provided by the test.
5. Select each of the sweep widths (these sweeps are centered about 10.7 MHz).
6. Reduce the span of the other spectrum analyzer to check that the cal oscillator is actually
sweeping. If the oscillator is not sweeping, perform the following steps:
a. The output of the sweep generator circuit (A4U804 pin 8 of function block Z) should
be a series of negative-going parabolas (frequency and amplitude vary depending on
the sweep width chosen). Table 9-3 lists the RANGE, MAO, and MA1 values for the
sweep widths. If a failure is indicated in the IF/LOG CHECK, press More Info to
provide more detailed information about the detected failure. If an HP-IB printer is
available, connect it to the HP 85623 spectrum analyzer HP-IB connector, then press
Print
Page
for a hard-copy output.
9-8 IF Section