2. Service
Top-Level Diagnostic Tree (Diagnostic Section 1)
55
1.3.7 CBT Depth-of-Modulation Warm-Up Errors
These errors usually indicate that modulation of CBT output signal that
results from tuning the microwave-probe signal through cesium resonance,
does not fall within minimal limits for correct operation. The errors can be
caused by incorrect operation of the microwave multiplication process (RF
chain), mis-tuning of the A19 VCXO (voltage-controlled crystal oscillator),
failure of the A7 C-field control circuits or rarely, failure of the CBT. The
following procedure checks these alternatives:
1 Test the RF chain by performing procedure 2.3.1.0. through 2.3.6.0.
2 Test the C-field circuit by performing procedure 2.4.1.0. through 2.4.3.0.
QUESTION: Did all diagnostic tests pass?
If Yes: The microwave signal is adequate for satisfactory warm-up
completion, Go to, 1.3.7.1.
If No: Repair as required and retest.
1.3.7.1 CBT Support-Circuit Tests
1 Perform the A19 VCXO tests 3.9.1.1 through 3.9.1.8).
2 Check the RF-level control current as described at 1.3.8.
3 When all tests complete satisfactorily, cycle power to the instrument.
QUESTION: Did warm-up fail with the same error message?
If Yes: CBT is probably defective, contact Symmetricom for further
assistance.
If No: Continue the diagnostic procedure.
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