2. Service
Top-Level Diagnostic Tree (Diagnostic Section 1)
54
1.3.5 Cs Oven-Timeout Test
This error occurs because the indicated cesium oven temperature has not
reached the correct value within 45 minutes from power on or an error has
subsequently occurred. This may be due to a failure of the cesium-oven
heater or thermistor, or the associated circuits on A2.
1 Perform the A2 Thermistor and Cesium Oven diagnostic test procedures in
diagnostic section 3 (3.1.2.1.0 and 3.1.4.1.0) of this chapter.
2 Replace A2 and/or A7 as indicated.
3 Reapply power to the instrument and observe the warm up behavior.
QUESTION: Did the instrument fail in the same manner?
If Yes: The CBT may be defective, contact Symmetricom for assistance.
If No: Continue diagnostic testing.
1.3.6 CBT Background-Signal Warm-Up Errors
These errors occur when the CBT background signal is not within acceptable
limits after warm up. This condition can be caused by a malfunction in the
CBT itself or by various circuits that control it. This procedure checks these
alternatives.
NOTE
The instrument self-tests must pass successfully for the following
procedure to be conclusive.
1 Perform the Electron-Multiplier Supply tests with procedure 3.7.2.1. Replace
A16 if necessary, and re-connect all leads.
2 Perform the Analog-Signal Chain tests 2.2.1.0. Repair as necessary, and re-
connect all cables and assemblies.
3 Retest the instrument by cycling ac power.
QUESTION: Does the instrument fail to lock-up, then display one of
the same errors?
If Yes: A CBT fault is indicated, contact Symmetricom for further assistance.
If No: Continue the diagnostic procedures.
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