Bell System 921A Maintenance Manual

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BELL SYSTEM PRACTICES
AT & TCo Standard
SECTION 107-402-500
Issue 2, September 1979
921A DATA TEST SET
MAINTENANCE
CONTENTS PAGE
1. GENERAL
2. MAINTENANCE AIDS 2
A. DTS Totally Inoperative 3
B. Self-Test Failure 4
C. Improper Operation 5
D. Verification of Repair 5
3.
MAINTENANCE PROCEDURES
8
A. Removal of Set From Carrying Case 8
B. Removal of Version 1 CPs From
Framework 10
C. Removal of Versions 2 and 3 CPs
From Framework 10
D. Replacement of CPs 10
E. Replacement of ROMs on CP 1
F. Replacement of ROMs on CPl 1
G. Replacement of DTS Into Carrying Case
1. GENERAL
11
13
13
1.01
This section contains troubleshooting procedures,
assembly and disassembly instructions, and
certain replacement procedures for the 921A data
test set (DTS) J79921A, Versions 1 through 3. The
version number appears on the DTS display when
RST is pressed, eg, 921A VERS #01 and on the
test code label in the cover. The replacement
procedures refer only to circuit packs (CPs) and
read-only memories (ROMs).
Ir
ft
When removing internal circuit packs
(CP1-CP6, CPll), care must be taken
to ensure that the boards are not
subjected to static electrical charges.
Such an occurrence can result in
destruction of sensitive integrated
circuits (ICs) or sufficient damage
to ICs to cause eventual failure.
Removal of CPs shouid be performed
in
an environment not susceptible
to static electrical charge buildup
and, personnel handling the boards
should be ugrounded." It is
recommended that personnel use
grounded, metal or conductive
plastic wrist straps with one
megohm series resistance. The
equipment used .to handle the
boards should be conductive. The
metal parts of associated fixtures,
tools, and table tops should be
grounded to a common point.
1 .02
This section is reissued to add coverage on
Version 3 of the 921A DTS.
1.03
In order to use the troubleshooting procedures
given in this section, a complete set of spare
circuit packs is required. · A list of these circuit
packs and their functions appears in Table A.
Included in the table are the accessories stored in
the DTS cover or cable accessory case ("saddle
bag") which are also shown in Fig.
1.
The chassis,
power supply, display, light emitting diodes (LEDs),
and other parts of the DTS which are not part of
the plug-in CPs are not repairable in the field.
If
the trouble cannot be cleared by replacement of
CPs, then the DTS must be returned to a Wes tern
Electric repair center.
NOTICE
Not for use or disclosure outside the
Bell System except under ~ritten agreement
Printed in U.S.A.
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