HP 8560A, Service Manual

Page: 418 / 450

3. Check maximum power available from the TG. Connect the RF OUT to the INPUT
Press LOG dB/DIV
TRACKING , SRC PWR ON , MORE OF 3 , ALC EXT. No connection should be
made to the ALC EXT INPUT connector on the rear panel. The available power should
always be greater than
If the output is unleveled only at specific frequencies, a
power hole will usually be visible at those frequencies.
4. Perform the LO OUTPUT Amplitude performance test. If the test fails, note the
Center Frequency setting at which the power level was out-of-tolerance. Repeat the test
with the power sensor connected to (a right-angle SMA adapter will be necessary)
and note the Center Frequency of any out-of-tolerance power levels. The power level should
be
If the power level is correct at W43 but out-of-tolerance at the LO OUTPUT (front
panel) and the Center Frequency setting of the out-of-tolerance power levels is close to the
frequencies at which the output is unleveled, suspect either A10 or W46.
If the power level at W43 is also out-of-tolerance, suspect either the A7 LODA or the All
YTO. Refer to Synthesizer Section Troubleshooting.
5. If the output is unleveled only at certain power level settings or certain frequencies,
monitor pin 1 with a DVM. Connect the negative DVM lead to pin 6.
Vary the TRK GEN RF POWER or Center Frequency settings, as appropriate, and plot
the voltage variation versus power level or frequency. A discontinuity in the plot near the
frequency or power level at which the output is unleveled indicates a problem on the Al4
Frequency Control Assembly.
Excessive Residual FM
Either the tracking oscillator or the ALC circuitry could be responsible for excessive residual
FM. The residual FM should be measured on another spectrum analyzer, such as an HP
or HP
using slope detection with the HP 8560A set to zero span.
Proceed as follows to troubleshoot residual FM problems:
1. Perform the Residual FM performance test for the spectrum analyzer in the Installation
and Verification Manual. If this test passes, the 1st LO input and 600 MHz drive signals
should be correct. If the test fails, troubleshoot the Synthesizer Section.
2. Monitor pin 15 (TUNE
with an oscilloscope. Connect the oscilloscope probe
ground lead to pin 6. The voltage at this point should be greater than 500 If
the voltage is less than 500 perform the Tracking Oscillator Range performance test in
the Installation and Verification Manual. If this test fails, perform the Tracking Oscillator
Range Adjustment. If the noise on this tune line is greater than 10
troubleshoot the
BITG Drive circuitry on A14.
3. Monitor the output of the tracking generator with another spectrum analyzer. Check
for high-amplitude spurious responses from 100 to at least 3 If the spurious
responses are too high in amplitude, the (broadband) ALC detector may cause the ALC
loop to oscillate, generating FM sidebands.. If any spurious responses are excessively high,
refer to Harmonic/Spurious Outputs Too High below.
4. If no spurious responses are present or are sufficiently low enough in amplitude to not cause
a problem, suspect the tracking oscillator in
11-20 RF Section