OK HUGE red flag to me is swapping the A23 Input Assembly.
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Unless you moved the calibration EERPOM over from the processor board? that's just about always going to fail on the receiver test if you have the SA option installed? ( which is fairly typical for most users )
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Also you can not swap the calibration EEPROM between an 8920A and 8920B.
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I would only repair the A23 modules for use in the same unit or move the EEPROM? ( which may cause some other complications )
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Not sure what an AA2 is ...is that the A2 Audio Analyzer board ?? ?What test is failing? Is it in the Audio Diags and the failure message.
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Also on the SINAD meter being pegged ...normal if there is no o signal present? with a 1Khz tone ...maybe an operational issue there.
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On the Output assembly low? is that from the RF diags? or operational .? If it's from the diags please provide the full failure descption.
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Best thing is to take one problem at a time .
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I would start with the RF diagnostics and getting those to pass.
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I would go back to you original A23 and calibration data? and go from there.
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I would have avoided upgrading the internal reference since that has issues in the field with warm up time and on the bench an external GPSDO would be a better option.
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