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 Time Slot Generation (Not a
Timing Diagram)
TDM Bus Diagram—3-Cabinet System
Equipment Connected to System 25 By
Call Processor and Port Circuit
Packs
Port Circuit Pack Common Circuitry
Unique Ground Start Trunk (ZTN76)
Circuitry
Unique Loop Start Trunk (ZTN77)
Circuitry
Unique Tip Ring Line (ZTN78) Circuitry
Unique ATL Line (ZTN79) Circuitry
Unique Data Line (TN726) Circuitry
Unique MET Line (TN735) Circuitry
Unique Analog Line (TN742) Circuitry
Unique DID Trunk (TN753) Circuitry
Unique Tie Trunk (TN760B) Circuitry
Tie Trunk (TN760B) Circuit Pack Option
Switches
3-2
3-4
3-6
3-9
3-11
3-15
3-17
3-20
3-22
3-26
3-30
3-32
3-34
3-36
3-38
3-40
3-42
3-44
3-46
3-48
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							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 the AT&T System 25 Maintenance Manual (555-500-105).
This manual includes information on Version 1 (V1) and Version 2 (V2). V2 is
primarily a software upgrade that provides the following:
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lEnhanced Data Services
STARLAN NETWORK Access
Switched Loop Attendant Console
Virtual Facilities
Miscellaneous Changes/Enhancements.
Required hardware for V2 includes a ZTN128 Processor circuit pack and a
ZTN127 Memory circuit pack. A ZTN84 STARLAN Interface circuit pack and
a switched loop attendant console are optional.
The maintenance procedures include:
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lObservation of alarm conditions;
Analysis of error messages and test results;
Performance of restoration procedures;
Replacement of system components; and
Performance of tests.
This manual is intended for use by a maintenance technician dispatched to a
System 25 site in response to an alarm or a user trouble report. The
technician must have completed the Tier 1 training course (T-335).
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							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.
Section 3. System Hardware—Describes the principal components of
the system, and provides detailed information on the switching network
and all circuit packs (CPs) supported by the system.
Section 4. System Software—Describes the system software resources
including switched services software, administration software, and
maintenance software.
Section 5. Maintenance Strategy—Provides an overview of the
maintenance process.
Section 6. Error Log—
Presents the format for error records and
examples of error messages with explanations.
Section 7. Operating the Digital Tape Unit—
Provides operating
instructions for the digital tape recorder to save and restore translations.
Section 8. Clearing System-Detected Troubles—
Provides general
trouble-clearing techniques and procedures for clearing specific system
troubles.
Section 9. Clearing User-Reported Troubles—
Describes user
complaints and provides procedures for clearing them.
Section 10. Reference Documentation—
Provides a list of other
System 25 documentation that may be valuable to the maintenance
technician.
Section 11. Abbreviations and Acronyms—Provides a list of
abbreviations and acronyms used in System 25 documentation.
Section 12. Glossary—Provides a definition of terms and acronyms
used in System 25 documentation.
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							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 screwdrivers
Long-nosed pliers
Regular pliers
Wrist grounding strap
Model DC4 Digital Tape Unit, with 355A adapter and a D8W cord
(Comcode 404079429)
Administration terminal (TI 703KSR or equivalent), with 355A adapter
(Comcode 404079436).
An oscilloscope is not needed for the Tier 1 maintenance procedures
provided in this manual.
Assumption
The information provided in this manual assumes that the system was initially
installed and tested in accordance with the Installation and Test Manual (555-
520-100).
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							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. Damage to integrated circuits via
electrostatic discharge may not be immediately apparent.
DANGER: Do not clip the wrist grounding strap to any cabinet location
other than the grounding block. Do not clip the wrist
grounding cord to a CP.
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							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 objects). Each object is normally a separately replaceable
unit. Examples include circuit packs (CPs), power supplies, fan assemblies,
the Digital Tape Unit, AC Power Distribution Unit, voice terminals, lines, and
trunks.
There are two general categories of troubles in system maintenance:
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lSystem-Detected Errors
User-Reported Troubles.
For system-detected errors, a light-emitting diode (LED) on the Attendant
Console is automatically lighted if the error qualifies as an alarm. This is a
serious error. Most alarms are also indicated by LEDs on system CPs.
User-reported troubles usually result from service problems at individual
voice and data terminals and are often related to alarmed conditions.
Error records and alarms are retired either automatically or manually. After a
trouble or error has been cleared, the system retests the previously faulty
area within a variable time interval. When the error is no longer detected, the
error message, and alarm if applicable, is retired. Maintenance personnel
may choose to retire error records and alarms manually after a problem has
been fixed by entering commands at the System Administration Terminal
(SAT). Using the SAT, error records can be accessed, listed, and removed.
Certain errors may not be removed. On the other hand, some alarms must
be cleared manually. After the error messages have been removed from the
error tables, the Attendant Alarm LED (and red CP LEDs) will go dark—
unless the trouble recurs.
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							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 Alarm table. This type of alarm also lights a red LED
on an associated CP. The LED, when lighted, is a visual signal that
service is required.
Transient System Errors:These are potential failures that may cause
degradation of service, although they do not light the Alarm LED on the
Attendant Console. Transient System Errors are errors that have not yet
been verified by system self-tests, and/or have not reached the level of a
Permanent System Alarm.
If a Transient System Error is verified or reaches a certain threshold
level of severity, it is reclassified as a Permanent System Alarm, and the
Alarm LED on the Attendant Console lights. Transient system errors are
stored in the Transient System Error table. The system stores up to 40
Permanent System Alarms and Transient System Errors in their
respective tables in the error log.
Most Recent System Errors:These are the ten most recent errors
recorded by the system, regardless of their severity. They do not light
the Alarm LED on the Attendant Console, unless they escalate to a
Permanent System Alarm.
Error Log
The three error tables can be displayed on the System Administration
Terminal (SAT). The error tables are very useful in diagnosing and analyzing
problems, particularly when the problem has not caused an alarm or when
alarms cannot be retired by replacement of maintenance objects.
The error tables are organized by time of occurrence. Unresolved errors are
listed, as well as past alarms providing a profile of past and current state of
the system. Example error records are provided in the Error Log description.
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							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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lAttendant Console:A green Alarm LED is provided to indicate the
presence of a Permanent System Alarm. The LED flashes with each
new alarm. The attendant can press the associated button to cause the
LED to light steadily.
Circuit Packs (CPs):LEDs are provided on the front edge of the CPs.
The LEDs are visible when the front cover of the cabinet is removed.
When lighted, these LEDs indicate the status of the CP as follows:
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lPort CPs:
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Red—On several seconds during power up and test, Off
with test pass, and On if fault in CP or associated trunk is
detected.
—Green—On indicates call resource available (port capable
of processing calls).
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Yellow—On indicates a call in progress, Off when not in
use.
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No LEDs Lighted—CP is not translated.
Memory CP—Red status LED—On several seconds during
power up and test, Off with test pass. After test pass, On if
fault in CP is detected.
Service Circuit CP—Same as port CPs except yellow LED flashes
(that is, flashes when busy). Steady Off indicates a CP problem.
Steady On indicates a tone receiver is being used.
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