HP 8560E, Service Manual

Page: 420 / 665

Chapter 8 419
IF Section
Performance Test Failures
Performance Test Failures
Failures in IF-Section-related performance tests may be investigated
using the following information:
IF Gain Uncertainty Performance Test
Failure of this performance test indicates a possible problem with the
spectrum analyzer IF gain circuits. Assuming no major IF problems
causing IF adjustment errors, IF gain problems in the first 50 dB of IF
gain (REF LVLs of 0 dBm to
−
50 dBm with 10 dB ATTEN) are a result
of faults on the A5 IF Assembly. IF gain problems in the next 60 dB of
IF gain (REF LVLs of
−
60 dBm to
−
110 dBm, 10 dB ATTEN) result from
log amplifier faults on the A4 assembly.
A signal level of
−
5 dBm is required at input (A5J3) for displaying a
signal at top screen with 10 dB input attenuation and a 0 dBm
reference level. Isolate IF gain problems on the log amplifier assembly
(A4) with the following steps:
1. On the spectrum analyzer press
PRESET
,
SPAN
,
ZERO
SPAN
,
FREQUENCY
, 1
GHz
,
AMPLITUDE
,
−
50 dBm.
2. Press
CAL
and
IF ADJ OFF
.
3. Disconnect cable W27 (coax 3) from A5J5 and connect cable W27 to
the output of a signal generator.
4. Set the signal generator controls as follows:
Amplitude ............................................................. +10 dBm
Frequency ............................................................ 10.7 MHz
5. Simultaneously decrease the signal generator output and the
spectrum analyzer REF LVL in 10 dB steps. The signal displayed by
the spectrum analyzer should remain at the reference level for each
step. If the signal deviates from the reference level, troubleshoot the
video offset circuitry on the A4 assembly.
6. Repeat steps 1 through 5 with the spectrum analyzer set to linear.