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Texas Instruments 990 User Manual
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Table
2-7.
Fault
Isolation
Procedures
When
Unable
to
Load
Diagnostic
~
Step
Symptom
Probable
Cause
Troubleshooting
Procedure
Normal
Indication
If
Abnormal
\0
~
Diagnostic
does
not
Constant
keyboard
Scope
circuit.
Logic
1
at
P2-66
Trace
back
until
fault
is
Ul
~
execute
interrupt
{Pl-66
for
2nd
located.
Replace
faulty
N
~
controller).
component(s).
\o
-....)
0
-
2
Diagnostic
does
not
Master
clear
not
Scope
circuit.
Logic
1
at
P2-66
Trace
back
until
fault
is
load,
test
LED
functioning
or
{Pl
-66
for
2nd
located.
Replace
faulty
lighted
always
active
controller).
component(s).
3
Diagnostic
does
not
CRU
interface
signal
Master
clear
system
CRUBIT12
=
0
Remove
CPU
or
CPU
load
shorted
to
another
(cycle
chassis
power
CRUBIT13
=
0
buff
er.
Ground
each
signal
or
to
ground
off
and
back
on)
CRUBIT14
=
0
input.
Check
effect
of
CRUBIT
15
=
0
grounded
input
on
other
CRUBITOUT
=
0
input.
Check
continuity
STORECLOCK-
=
1
to
locate
short
circuit
MODSELA-
=
1
path.
Repair.
N
I
MODSELB-
=
1
N
-
CR
UBITINT
=
1
NKBINT
=
1
4
Diagnostic
does
not
CRU
interface
signal(s)
Same
as
for
step
3
Same
as
for
step
3.
Remove
VDT
controller.
load,
CRU
lines
not
shorted
to
ground
Check
CRUBIT,
12-15,
shorted
to
each
and
CRUBITOUT
for
other
ground.
122
124
Table of Contents
Table of Contents
5
Paragraph Title Page
6
Section I. Theory of Operation
11
General
11
System Description
11
CRT Monitor
12
Power/Logic PWB
13
VDT Controller
17
Interface Descriptions
19
VDT Controller/Computer Interface
20
Single-Bit Operations
20
Multiple-Bit Operations
20
Hardware Interface Signals
22
Keyboard Data (KBDT, 1-8)
28
Keyboard Data Strobe (KBSIN-)
29
Power/Logic PWB-To-VDT Controller Interface
29
Keyboard Data (TET,1,2,T)
29
Terminal Ready (TRD, 1, 2, T)
29
VDT Controller-To-Power/Logic PWB Interface
29
Beep Enable (BET, 1, 2, T)
32
Modem Audio (MODIN)
32
Principles of Operation
33
Mode Keys and Mode Select Logic
33
Power/Logic PWB
34
Buffer Register
45
LED Display
45
Difference Amplifier
53
CRT Monitor
54
CRT Interface Logic
56
Built-In Test Logic
56
Keyboard Logic
57
Model 911 VDT Controller Block Diagram
59
Video Line Driver
61
CRU Interface Logic
62
Model 911 VDT Keyboard Logic
63
CRU Interface Logic
65
Refresh Memory and Control Logic
69
Refresh Memory Block Diagram
70
Refresh Memory Data Path
73
Memory Read and Write Control Logic
75
Memory Addressing Logic
77
Flowchart for Memory Write Operation
79
Flowchart for Memory Read Operation
80
Display Screen Refresh Cycle Flowchart
81
Video Output Logic
83
Model 911 VDT Character Matrix Formats
85
Model 911 VDT Displayed United States Character Set, Including Graphics Symbols
87
Model 911 VDT Alarm Logic
89
Model 911 VDT Time Base Generator Character Synchronization Logic
93
Model 911 VDT Dot Counter Outputs
95
Model 911 VDT Sync Timing Diagram
101
Section II. Maintenance
103
General
103
Maintenance Philosophy
103
Special Test Equipment
103
Model 990 Computer Hot Mock-Up System for 60-Hertz Model 911 VDT Testing
104
Hot Mock-Up System
106
Loading the Diagnostic
106
Using the Diagnostic
106
CD Verb Entry
109
General Maintenance Procedures
110
PWB Preliminary Checkout
110
General Fault Isolation Procedures
110
Keyboard Maintenance Procedures
110
Keyboard Preliminary Checkout
110
Keyboard Fault Isolation Procedures
111
Keyboard Operational Checkout
114
Power/Logic PWB Maintenance Procedures
114
Power/Logic PWB Preliminary Checkout
115
Power/Logic PWB Fault Isolation Procedures
115
VDT Controller Maintenance Procedures
115
VDT Controller Fault Isolation Procedures
118
CRT Monitor Maintenance Procedures
118
CRT Monitor Preliminary Checkout
118
CRT Monitor Fault Isolation Procedures
118
VDT Controller Assembly Configuration
119
CRU Interface Waveforms During Exercise by the CD-C Verb
125
Timer Signal Relationships
128
Alarm Signal Timing Diagram
131
Model 911 VDT Controller Keyboard Logic Timing Diagram
133
United Kingdom Model 911 VDT Keyboard Arrangement, Hexadecimal Codes, Mode Character Positions, ASCII, Special Character Set, and Matrix Chart
147
United Kingdom Model 911 VDT Keyboard Matrix Chart
153
French Model 911 VDT Keyboard Arrangement, Hexadecimal Codes, Mode Character Positions, ASCII, Special Character Set, and Matrix Chart
154
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Texas Instruments 990 Specifications
General
Brand
Texas Instruments
Model
990
Category
Desktop
Language
English
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