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TRS-80 Model III
Radio Shack TRS-80 Model III Service Manual
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1
3
Table of Contents
Table of Contents
3
List of Illustrations
5
List of Tables
7
Introduction
9
System Overview
11
TRS-80 Model III Block Diagram
12
Disassembly/Reassembly
13
Disassembly
15
Case
15
CPU Board
15
FDC Board
15
Video Monitor (CRT) and Video Board
16
Reassembly
17
RS-232 Board
17
Main Power Supply
17
Disk Drive
17
CPU Circuit Board
19
Technical Description
21
Video SYNC Circuits
21
Processor
21
Ram
21
Address Decoding
22
Memory Map of Model III
22
IO Port Description
23
Video
24
Video Timing Diagram
24
Keyboard
25
Cassette Interface
25
Adjustments and Jumper Positions
26
Line Printer and Real Time Clock
26
IO Bus
26
Model III IO Bus
27
Input or Output Cycles
28
Input or Output Cycles with Wait States
28
IO Bus Timing Diagrams
28
Model III Port Bits
29
CPU Printed Circuit Board - Component Side
31
CPU Printed Circuit Board - Circuit Side
32
CPU Module Parts List
33
Model III CPU Schematic Diagram - Video and Horizontal Sync Circuits
39
Model III CPU Schematic Diagram - Processor Section
40
Model III CPU Schematic Diagram - RAM Section
41
Model III CPU Schematic Diagram - Address Decoding Section
42
Model III CPU Schematic Diagram - Video Section
43
Model III CPU Schematic Diagram - Keyboard Section
44
Model III CPU Schematic Diagram - Cassette Interface Section
45
Model III CPU Schematic Diagram - Line Printer and Real Time Clock Section
46
Model III CPU Schematic Diagram - I/O Bus Section
47
Model III CPU Schematic Diagram - RS-232-C Interface and FDC Interface Connectors
48
Floppy Disk Interface
49
Control and Data Buffering
51
Nonmaskable Interrupt Logic
51
Drive Select Latch and Motor on Logic
51
Wait State Generation and Waitimout Logic
52
Clock Generation Logic
52
Disk Bus Selector Logic
52
Write Recompensation and Clock Recovery Logic
52
Adjustments and Jumper Options
53
Floppy Disk Controller Chip
53
Jumper Connections
53
FDC Board to CPU Board Signal Description
54
Floppy Disk Interface PC Board - Component Side
55
Floppy Disk Interface PC Board - Circuit Side
56
Floppy Disk Interface PC Board Parts List
57
Model III Floppy Disk Interface Schematic
59
RS-232C Circuit Board
61
RS-232C Technical Description
63
BRG Programming Table
63
Port and Bit Assignments
65
Port E8H
65
Port E9H
65
Port EAH
65
Port EBH
66
Port EAH Output Bits with Uart Control Register Disabled
66
Port EAH Input Bits
66
RS-232 Board to CPU Board Signal Description
67
RS-232C PC Board - Component Side
68
RS-232C PC Board - Circuit Side
69
RS-232C PC Board Parts List
70
Model III RS-232C Schematic Diagram
71
Power Supply
73
Functional Specifications
75
Troubleshooting
75
Equipment for Test Set-Up
75
Visual Inspection
75
No Output
76
Start-Up
76
Load Board Values
76
O2 Collector Waveform
76
Performance Test
77
Voltage and Ripple Specification
77
Power Supply Component Values
78
Power Supply Schematic Diagram
79
Video Monitor
81
Video Monitor Printed Circuit Board
84
Service Adjustments
85
Deflection Yoke Assembly
85
Video Monitor Assembly Schematic Diagram
86
Illustrated Parts Catalog
87
Outer Case Assembly
89
Case Top Assembly
90
Base Plate Assembly
91
Metal Chassis Assembly
92
Disk Drive Assembly
93
Illustrated Parts Catalog Parts List
94
Miscellaneous
96
Mini Disk Drive
99
General Description
101
Physical Description
101
Functional Description
101
Interface Connections
101
Physical Checkout
102
PC Board Component Locations
102
Logic Board (Component Side)
102
Non-Linear Servo Board (Component Side)
103
Linear Servo Board (Component Side)
103
Mounting the Disk Drive
104
Flat Ribbon Cable Assembly
104
Resistor Terminator
104
Cable Assembly - Connector Pin Removal Chart
104
Theory of Operation
105
Functional Block Diagram Description
105
Index
105
Spindle Drive
105
Data Electronics
106
Functional Block Diagram
106
FM Recording
106
Data Recording
107
Data Reproduction
107
Write Timing Diagram
108
Read Timing Diagram
108
Operation
109
Select Lines (DS1-DS4)
109
Direction and Step (DIR) (STEP)
109
Compensated Write Data (CWD)
109
Interface Connector PIN Assignments, J1 (External), J4 (Internal)
110
Power Connector PIN Assignment
110
Side Select (SDSEL)
111
Index Pulse (IP)
111
Write Protect (WPRT)
111
Read Data (RD)
111
Maintenance
113
Physical Description of the PC Boards
113
Circuit Board Test Points
113
Option Select
113
Logic Board Test Points and Connector Locations
114
Servo Board Connector Locations
115
Preventive Maintenance
116
Cleaning the Head
116
Alignment and Adjustment
116
Drive Motor Maintenance
116
Head Radial Alignment/Ce Alignment
117
"Cat Eyes" Pattern
117
Radial Adjustment
117
Track Alignment
118
Index Sector Adjustment
118
Track Stop Adjustment
118
Index Adjustment
118
Head Amplitude/Compliance Check
119
Final Check
119
Upper Arm and Carriage
119
Disk Controller Board Parts List
120
Servo (Motor Control) Board Parts List
124
Illustrated Parts Catalog - Exploded View
126
Mini-Disk Drive Schematic
128
Non-Linear Servo Board
130
Linear Servo Board
130
Mini-Disk Drive Schematic of New Board
131
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Radio Shack TRS-80 Model III Specifications
General
Brand
Radio Shack
Model
TRS-80 Model III
Category
Desktop
Language
English
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