E8257D/67D, E8663D PSG Signal Generators Service Guide
Troubleshooting
Troubleshooting ADC Adjustment Failures
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Troubleshooting ADC Adjustment Failures
The ADC adjustment adjusts the ADC reference voltage to match the A18 CPU +10 Vdc reference. There are three
reasons the adjustment could fail:
• problems with the +10 Vdc reference
• A18 CPU problems
• analog mux on another assembly is starting to fail
Procedure:
1. Run self–test 1100. If self–test 1100 passes, the +10 Vdc reference is good; proceed to step 2.
2. To see if an analog mux is failing and loading the supply, turn power off and remove the A5 Sampler, A6 Frac–N,
and A7 Reference.
3. Run the adjustment. If the adjustment passes, turn power off, reinstall one assembly at a time and run the
adjustment until the problem assembly is located.
4. If self–test fails, turn power off, reinstall the assemblies and remove the A8 Output, A9 YIG Driver, and A10 ALC.
5. Run the adjustment. If the adjustment passes, turn power off, reinstall one assembly at a time and run the
adjustment until the problem assembly is located.
6. If self–test fails, turn power off, reinstall the assemblies and remove the ribbon cable from J10 on the A26 MID
(W35).
7. If self–test passes, replace the A26 MID.
8. If self–test fails, replace A18 CPU.
Troubleshooting Performance Test Problems
If a performance test fails and all self–tests pass, use the following to find the most likely failure:
Performance test that is failing... Action to perform...
Maximum Leveled Output Power Refer to “Troubleshooting the RF Path” on page 1- 75.
Power Level Accuracy Perform
Power Flatness Calibration,
Attenuator Calibration–Lowband and Highband Power,
Attenuator Calibration–Highband and High Power,
Attenuator Calibration–Lowband and Low Power, and
Attenuator Calibration–Highband and Low Power.
Internal Pulse Modulation Level Accuracy
Internal Pulse Modulation Rise/Fall Time
Internal Pulse Modulation Minimum Pulse Width
If the frequency ≤3.2 GHz, check the
A11 Pulse/Analog Modulation Generator or the A8 Output.
If the frequency is >3.2 GHz, check
A11 Pulse/Analog Modulation Generator and the A10 ALC.
If the Internal Pulse Modulation Minimum Pulse Width test fails,
perform a Pulse Width Calibration prior to replacing any assembly.
DC FM Carrier Offset Perform DC FM Calibration.
If still failing, check A11 Pulse/Analog Modulation Generator and A6 Frac–N.
External AM Frequency Response If the frequency is ≤3.2 GHz, check the
A11 Pulse/Analog Modulation Generator or the A8 Output.
If the frequency is >3.2 GHz, check the
A11 Pulse/Analog Modulation Generator and the A10 ALC.
Internal FM Frequency Response Perform FM adjustments.
If still failing check A11 Pulse/Analog Modulation Generator and A6 Frac–N.
External Phase Modulation Frequency Response Perform FM adjustments.
If still failing check A11 Pulse/Analog Modulation Generator and A6 Frac–N.
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