AT&T System 25 - Manual (Page 185)

MAINTENANCE
MAINTENANCE STRATEGY
Fault isolation is the cornerstone of the System 25 maintenance strategy.
Maintenance activity isolates faults to one (or more) repairable or replaceable
maintenance units. Equipment should be tested in the following order:
1.
2.
3.
4.
5.
6.
Terminal equipment
Station wiring
Port circuit packs (CPs)
Common control circuitry
Power supply and cabinet
Backplane.
The first fault isolation step attempts to reproduce the fault, whether it is
system-detected or user-reported. A fault that can be reproduced is more
easily diagnosed and corrected.
Figure 4-1 presents a practical approach in responding to system troubles. If
the maintenance technician is sent to a System 25 site in response to a
trouble report, the maintenance activity will probably consist of isolating and
replacing one or more faulty units of equipment. However, multiple faults
recorded in the Error Log and user-reported troubles may require more
investigation and analysis’.
When the limits of trouble-clearing analysis are reached and the trouble is still
not cleared, the maintenance technician must escalate the problem to a
higher level of technical support.
Problems should be escalated to the
National Service Assistance Center (NSAC) in Denver, Colorado. The
telephone number is 1-800-628-2888.
4-9