2. Service
Top-Level Diagnostic Tree (Diagnostic Section 1)
53
1.3.3 CBT-Signal Fatal Errors
These errors occur when the instrument completes its lock-up procedure, and
the frequency servo loop cannot operate correctly. They usually indicate the
CBT output signal is unstable. This can be due to a malfunction in the CBT
itself, or more frequently, in the circuits associated with it. The following
procedure tests these alternatives.
1 Perform the Analog-Signal Chain tests (2.2.1.0) and repair as required.
2 Perform the RF-Chain tests (2.3.1.0) and repair as required.
3 Perform the A16 Electron-Multiplier Supply tests (3.7.2.1) and repair as
required.
4 Perform the RF-Level Control-Current Check, (1.3.8), and repair as required.
5 Apply power to the instrument: observe the warm up and subsequent
operation.
QUESTION: Did the instrument fail in the same manner?
If Yes: The CBT is possibly defective, contact Symmetricom for further
assistance.
If No: Problem may be resolved - retest.
1.3.4 CBT Shutdown Message
1 Read the CBT shutdown message preceding the error code.
QUESTION: What is the message?
If CBT shutdown:
thermistor open, Go to, A2 thermistor
(3.1.2.1.0) diagnostic tree.
If CBT shutdown:
thermistor shorted, Go to, A2 thermistor
(3.1.2.1.0) diagnostic tree.
If CBT shutdown:
ion pump overcurrent, Go to, Excess Ion-
pump current (1.3.2.1) test.
If CBT shutdown:
E-mult adjust failed – This indicates that although
larger e-mult movements were attempted the internal CBT parameters
could not be compensated sufficiently to allow continued operation.
Repair is likely necessary, however a re-start of the 5071A should first
be attempted as a possible remedy. If the failure re-occurs with the
same message, contact Symmetricom to arrange repair/replacement of
the CBT. If the error is not repeated but another error occurs, follow the
procedures for that error.
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