ATT System 25 Maintenance Manual

List of Figures
Figure 3-1.
Figure 3-2.
Figure 3-3.
Figure 3-4.
Figure 3-5.
Figure 3-6.
Figure 3-7.
Figure 3-8.
Figure 3-9.
Figure 3-10.
Figure 3-11.
Figure 3-12.
Figure 3-13.
Figure 3-14.
Figure 3-15.
Figure 3-16.
Figure 3-17.
Figure 3-18.
Figure 3-19.
Figure 3-20.System 25 Block Diagram
Typical Station Interconnect Panel (SIP)
Connections
Trunk Access Equipment Connections
System 25 Digital Switch
Call Processor [ZTN82 (V1) or ZTN128
(V2)] Circuitry
Memory [ZTN81 (V1) or ZTN127 (V2)]
Circuitry
TDM Bus...

Figure 3-21.
Figure 3-22.
Figure 3-23.
Figure 3-24.
Figure 4-1.
Figure 5-1.
Figure 8-1.
Figure 8-2.
Figure 8-3.
Figure 8-4.Unique Auxiliary Trunk (TN763)
Circuitry
3-50
Service Circuit (ZTN85)3-53
Tone Detector (TN748) Circuit3-55
Pooled Modem (TN758) Circuit3-57
System Software Partitioning4-6
Response to System 25 Trouble Report5-2
AC Power Schematic8-15
System Cabinet Backplane8-19
TDM Signal Designations On Cabinet
Backplane
8-21
Power Designations On Cabinet
Backplane
8-22
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List of Tables
Table 3-A.
Table 3-B.
Table 3-C.
Table 8-A.
Table 8-B.
Table 8-C.
Table 9-A.
Table 9-B.TDM Bus Time Slots
TN760B Option Switch Settings and
Administration
Signaling Type Summary
Displayed SAT Messages During Cold
or Warm Restart
Circuit Pack Voltages—Symptoms
25-Pair Connector to Backplane
Designations
Station/Trunk/Special Port Circuit
Board Options
Applicable Actions for Circuit Board
Options3-18
3-47
3-48
8-6
8-13
8-24
9-10
9-11
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INTRODUCTION
This manual provides the information necessary for monitoring, testing, and
maintaining AT&T System 25 (Release 1 Version 1 and Release 1 Version 2).
The modular self-testing capabilities of the system allow most maintenance to
be reduced to simple procedures.
This issue replaces all previous issues of this manual. This manual is
reissued to include changes in System 25 maintenance strategy that enhance
product safety and to make minor corrections in the previous issue.
This manual replaces...

INTRODUCTION
Each installed System 25 has a customer-designated System Administrator.
The Administration and Implementation Manuals for your system describe the
administrators functions. The maintenance technician should work closely
with the System Administrator.
Organization
This manual is divided into 13 sections. The remaining sections are as
follows:
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lSection 2. General Maintenance Information—Provides an overview of
alarms, maintenance concepts, equipment, and basic procedures....

INTRODUCTION
lSection 13. Index—Provides an alphabetical listing of principal subjects
covered in this manual.
Equipment Needed
The following tools and equipment should be taken by the maintenance
technician on any System 25 service call:
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lEIA breakout box
Digital voltmeter (KS-20599 or equivalent)
Modular cord breakout box
110-type punchdown tool (AT 8762D or equivalent)
Dracon TS21 or equivalent touch-tone test set
Assorted flat-head screwdrivers
Assorted Phillips-head...

INTRODUCTION
Precautions
Electromagnetic fields radiating from the system cabinets may generate noise
in other communications equipment. The technician must be sure that all
cabinet panels and covers are securely in place after performing
maintenance.
WARNING: Electrostatic discharge can destroy or severely damage
integrated circuits or CPs.
The maintenance technician MUST ALWAYS WEAR A WRIST GROUNDING
STRAP when handling CPs. The cord must be attached to the grounding
block at the back of the cabinet....

GENERAL MAINTENANCE INFORMATION
The primary maintenance objective is to detect, report, and clear troubles as
quickly as possible with minimum disruption to normal service. Periodic
system self-tests, automatic software diagnostic programs, and fault
detection hardware are several of the maintenance tools used to achieve this
objective. The system design allows most troubles to be isolated to a
replaceable unit.
The System 25 hardware is maintained as a group of independent units (that
is, maintenance...

GENERAL MAINTENANCE INFORMATION
System Errors and Alarms
When a system maintenance object begins to fail periodic testing, the system
automatically generates an error record. Depending on severity, the record is
stored in one of three tables in the error log.
The three tables are:
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lPermanent System Alarms:These are failures that cause degradation of
service and require immediate attention. These alarms will light the
Alarm LED on the Attendant Console and are stored in the Error Log
Permanent System...

GENERAL MAINTENANCE INFORMATION
Emergency Transfer
System 25 has emergency transfer capability in case of total system outage.
Emergency transfer connects preassigned single-line voice terminals directly
to trunks that are connected directly to the CO, bypassing the System 25.
Emergency transfer is invoked by loss of ac power or by any failure of the
system that prevents it from processing calls.
Alarm and Status Indicators
Maintenance-related LED indicators are provided on the following equipment:
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