
8712ET/ES and 8714ET/ES Troubleshooting and Block Diagrams
RF Network Analyzers Category 2 Failures: No Error Messages but One or More Measurements Are Nonfunctional
Service Guide 4-21
Testing the DSP Circuit
To check the DSP circuit, substitute the receivers’s ADC clock and data signals with
similar signals created on the CPU board.
1. Turn off the analyzer and remove the CPU board (refer to “Removing the CPU Board
Assembly” on page 3-6).
2. Locate J702 on the CPU assembly (J702 is an eight-by-three jumper located above the
DSP metal shield). Temporarily place the jumper in the TEST position as marked on
the board. The replacement signals will now be created by the CPU board.
3. Power-up the instrument and observe the analyzer display. Follow the instructions
below:
a. If a random noisy trace is observed around 0 dB, the CPU board assembly is
functioning properly. Replace the receiver PC board of the receiver assembly (A5).
(Refer to “Removing the Receiver PC Board” on page 3-14.) For additional
confirmation of the need to replace the receiver PC board, perform the steps in
“Troubleshooting the Receiver ADC” on page 4-32.
b. If no random noisy trace is observed around 0 dB, replace the CPU board assembly.
(Refer to “Removing the CPU Board Assembly” on page 3-6.)
c. Return the jumper at J702 to its normal position.
Symptom 2: All Traces Are Below −10dB
This symptom indicates that no power is reaching any of the detectors.
1. Measure the RF output power level from the source (A4) at A4J4. Press
.
a. If the power level is below −5 dBm, replace the source assembly (A4). (Refer to
“Removing the Source Assembly” on page 3-11.)
b. If the power level is above −5 dBm, this indicates that the limiter in the source path
on the receiver board is damaged. Replace the source limiter (refer to “Removing the
Limiter (ET Analyzers)” on page 3-18).
c. If the problem persists, the R coupler could be damaged. Replace the R coupler (refer
to “Removing the Coupler” on page 3-15).
Symptom 3: R* and B* Traces Are Normal, All Others Noisy
If the broadband detectors give a normal response and the narrowband detectors are noisy,
the LO source could be damaged. To verify this, follow these steps:
1. Perform “Verifying the 10 MHz reference signal” on page 4-30.
a. If the 10 MHz verify process fails, it indicates a problem with the 10 MHz reference
circuit. Replace the fractional-N/reference assembly (A3). (Refer to “Removing the
Fractional-N/Reference Assembly” on page 3-10.)
b. If the 10 MHz verify process passes, a problem with the LO source on the source
board could exist. Replace the source assembly (A4). (Refer to “Removing the Source
Assembly” on page 3-11.)
FREQ
50
POWER 0
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