
Troubleshooting and Block Diagrams 8712ET/ES and 8714ET/ES
Category 3 Failures: Inaccurate (but reasonably functional) Measurements RF Network Analyzers
4-34 Service Guide
Troubleshooting Trace Drift for ET Models.
To check the uncorrected performance of the analyzer, follow the steps below. Refer to
Figure 4-4 on page 4-19 and Figure 4-5 on page 4-20 for the part designators.
Checking the Uncorrected Directivity of the RF OUT Coupler
1. Set the analyzer to the default condition by pressing .
2. To turn off calibrations, press
.
3. Leave the RF OUT port open.
4. Press .
5. Attach a good load to the RF OUT port (preferably from a calibration kit).
6. The directivity limits are −25 dB for a 50Ω analyzer and −15 dB for a 75Ω analyzer.
Compare the trace to the appropriate limit.
a. Replace the A coupler if any part of the trace is above the appropriate limit. Refer to
“Removing the Coupler” on page 3-15.
7. If the uncorrected directivity for RF OUT passes, go to “Checking the Uncorrected
Directivity of the R Coupler and the Load Match of RF IN.”
Checking the Uncorrected Directivity of the R Coupler and the Load Match of RF IN
1. Leave the load connected to the RF OUT port and display the trace for the R detector by
pressing .
2. Normalize the load response for use as a reference by pressing
. (Pressing twice will update the reference trace.)
3. Remove the load from the RF OUT connector. All of the trace should be between +5 dB
and −5 dB. If it is outside this range, the directivity of the R coupler is unacceptable.
Replace the R coupler from the receiver assembly (A5).
4. If the previous checks passed, remove the load and connect a high quality thru cable
between the RF OUT and RF IN connectors.
5. Turn off the normalization by pressing .
6. Press .
7. If the max point of the trace is above −12 dB, there is a port match problem in the RF IN
path. Replace the limiter in the B input path. If the problem persists, replace the
receiver PC board on the receiver assembly (A5). (Refer to “Removing the Receiver PC
Board” on page 3-14.)
PRESET
POWER 0
SYSTEM OPTIONS
MEAS 1
CAL
MEAS 1
CAL
CAL
MEAS 1
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