Flatness Out-Of-Tolerance; Vernier Accuracy Out-Of-Tolerance - HP 8560A Service Manual

Flatness Out-of-Tolerance

The output level flatness of the tracking generator is specified at a 0 dBm output power
setting. In general, most flatness problems will be a result of a failure in the A10 Tracking
Generator microcircuit. However the POWER LVL signal from the Al4 Frequency Control
Assembly and the 1ST LO IN signal from the A7 LODA can also contribute to flatness
problems.
1. Check the function of the POWER LVL signal from the Al4 Frequency Control Assembly.
Set the TRK GEN RF POWER to a level at which the flatness is out-of-tolerance.
Monitor A17J16 pin 1 with a DVM and step the Center Frequency in 100 MHz increments
from 100 MHz to 2.9 GHz and plot the voltage variation versus frequency. A discontinuity
in the plot near the frequency at which the flatness is out-of-tolerance indicates a problem
on the Al4 Frequency Control Assembly.
2. Check the flatness of the 1ST LO IN signal. Perform the 1ST LO OUTPUT Amplitude
performance test. If the test passes, the fault is most likely in the A10 Tracking
Generator. If the test fails, note the Center Frequency setting at which the power level
was out-of-tolerance and compare against the frequency(ies) at which the flatness was
out-of-tolerance. Repeat the test with the power sensor connected to the end of W43
nearest AlO, noting the Center Frequency of any out-of-tolerance power levels. The power
level should be +16.5 dBm f2 dB.
If the power level is correct at W43 but out-of-tolerance at the 1ST LO OUTPUT and the
Center Frequency setting of the out-of-tolerance power levels is close to the frequencies at
which the output is unleveled, suspect AlO.
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.
3. Check all coax cables, especially semi-rigid cables. A fault in one of these cables can cause
a very high-Q power hole.

Vernier Accuracy Out-of-Tolerance

Vernier accuracy is a function of the POWER LVL drive signal from the Al4 Frequency
Control Assembly and the ALC circuitry on AlO. The vernier accuracy is specified at
300 MHz. Since vernier accuracy is tested using a broadband power sensor, abnormally high
spurious responses could cause the measured vernier accuracy to fail when in fact the accuracy
of the 300 MHz signal alone is within specification.
1. Check the POWER LVL drive signal from A14. Monitor A17J16 pin 1 with a DVM.
Change the TRK GEN RF POWER in 1 dB steps and note the voltage at each power
level setting. The voltage should change by the same amount for each 1 dB step. If the
voltage does not change by the same amount for each 1 dB step, the fault lies on the Al4
Frequency Control Assembly.
2. Check for abnormally high spurious outputs. Connect the RF OUT 5OQ to the input of
another spectrum analyzer (the "test analyzer"). Set the test analyzer to sweep from
300 kHz to 2.9 GHz, with a sweeptime of 100 msec or less. Set the HP 8560A to sweep
from 300 kHz to 2.9 GHz with a 50 second sweeptime. Press (SGLSWP) on the HP 8560A
and observe any responses on the test analyzer, ignoring the desired output signal. If any
spurious responses are greater than -20 dBc, the vernier accuracy measurement may fail.
Refer to Harmonic/Spurious Outputs Too High.
RF Section 11-21