Agilent Technologies 85032B/E 50 Specifiche Pagina 174

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Troubleshooting and Block Diagrams 8712ET/ES and 8714ET/ES
Category 2 Failures: No Error Messages but One or More Measurements Are Nonfunctional RF Network Analyzers
4-32 Service Guide
Checking the LO Output
Now check the LO output from the source at A4J1. Use the same conditions as above.
1. Measure the LO when the RF out is set to 50 MHz. The LO should always be
27.778 kHz above the RF signal. Repeat for 3000 MHz (1300 MHz for 8712ET/ES).
Power levels for the LO should be in the +2.0 to +14 dBm (+6 to +14 dBm range for the
8712ET/ES), regardless of frequency.
If either of the outputs from the source board (A4) are not correct when the inputs from the
A3 fraction-N/reference board are correct, replace the source board (refer to “Removing the
Source Assembly” on page 3-11).
Troubleshooting the Receiver ADC
NOTE This process should only be used after the results of the “Testing the DSP
Circuit” procedure under Symptom 1 indicate that the CPU board is
functioning properly. This process may be used to confirm a problem with the
ADC circuits on the receiver board.
CAUTION If you are performing this test after “Testing the DSP Circuit,” ensure that
jumper J702 on the CPU (A2) board is returned to its normal position.
To confirm an ADC problem when the trace is at ±200 dB, check for activity at the
receiver’s backplane connector.
1. Remove the metal cover on the back of the instrument to access the backplane. The
receiver connector is at the bottom of the analyzer and is labeled XA5J1 on the PC
board.
2. Check the pins listed in the following table.
Table 4-3 Backplane Signal Activity at the Receiver Connector (XA5J1)
3. If any of these signals is a DC level (which means no activity), replace the receiver PC
board from the receiver assembly (A5). (Refer to “Removing the Receiver PC Board” on
page 3-14.)
Pin Number Type of Signal
C27 ADC_DAT1
A27 ADC_CLK1
C26 ADC_DAT2
A26 ADC_CLK2
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