2. Service
Top-Level Diagnostic Tree (Diagnostic Section 1)
52
1.3.2.1 Cs Oven Failed: Ion Pump Overcurrent Warm-up Error
This error occurs when current drawn by the CBT Ion Pump fails to go
below 40 A within 45 minutes after operation begins. It can be
caused by either excessive current drawn by the CBT as a result of a
high internal gas pressure, or by a failure in the Ion pump high-voltage
supply (P/O A16), or the current-monitoring circuit (P/O A2). The
following procedures check these alternatives:
1 Observe the measured Ion-Pump supply current on the LCD display
(Use the INFO/Pump menu selection.).
QUESTION: Is the current more than 40 A?
If Yes: Go to, 1.3.2.2.
If No: The problem may have cleared itself, remove ac power,
and retest.
1.3.2.2 A16/CBT Excess Ion-Pump Current Test
1 Remove instrument power and wait at least 60 seconds for the high voltage
supplies to bleed down.
2 Disconnect the Ion Pump high-voltage (HV) connector from the CBT (see
Figure 2.1). (Ensure that the end of the high-voltage lead is clear of any
conductors.)
3 Disconnect the flexible cable joining the CBT to A2J2.
4 Power up the instrument and allow a few seconds for it to enter the Fatal-
Error mode.
5 Observe the measured Ion Pump supply current on the LCD display (Use the
INFO/Pump menu selection.).
6 Remove power, wait 1 minute, and reconnect the Ion-pump HV lead.
QUESTION: Was the current more than 1 microamp?
If Yes: A fault is present in the Ion Pump power supply circuitry,
Go to, 3.7.1.0, A16 diagnostic tree (This tree also checks part of
A2.).
If No: CBT Ion-Pump current is high. When caused by poor vacuum (for
example, due to prolonged storage) the condition may correct
itself if the unit is placed into STANDBY mode for 24 hours. If the
condition persists after this time, remove power and contact
Symmetricom for assistance.
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