Radio Shack TRS-80 User manual

•
ervlce
CUSTOM MANUFACTURED IN U.S.A. BY RADIO SHACK, ADIVISION OF TANDY CORPORATION

TRS-80"' Model 4Pi4P Gate Array Service Manual
Copyright" 1984 Tandy Corporation
All Rights Reserved.
Reproduction or use, without express written permission from Tandy Corporation. of any
portion of this manual is prohibited. While reasonable efforts have been taken
in the
preparation of this manual to assure its accuracy, Tandy Corporation assumes no liability
resulting from any errors or omissions
in this manual, or from the use of the information
contained herein.

SECTION I
1.1
1.2
1.3
SECTION
II
2.1
2.2
2.3
2.4
2.5
SECTION
III
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
TABLE OF CONTENTS
Introduction. ...................................................................... 1
SystemOverview
.. ................................................................ 3
Optionai Features. ................................................................. 3
System BlockDiagram. ............................................................. 5
Specifications ..................................................................... 7
Microprocessor. ................................................................... 9
Peripheral Interfaces................................................................ 9
PowerRequirements 9
OperatingTemperature 9
Dimensions ....................................................................... 9
Disassembly/Assembly
11
Case 13
Internal Rear Mounting Plate. .. ........................ .. .......................... .. 13
FrontBezel. .....
.. ...... .. ........................ .. .. .............. .. .. .. ...... .. 13
Top Cover/Power Supply. . .. ...... .. ...... .. ........ .. .............. .. .......... .. .. 13
CathodeRayTube 14
CRTSweepBoard 14
Main Logic PCB. ................................................................. .. 14
KeyboardAssembly .............................................................. .. 14
DiskDriveAssembly. .............................. .. ..... .. .. .. .. .. .. . . .. .. ...... .. 15
Control Module ................................ 15
SECTION IV Maintenance/Troubleshooting (general suggestions, reference
to section below for specific troubleshooting hints) ....................................
.. 17
SECTION V
5.1
5.1.1
5.1.2
5.1.3
5.1.4
5.1.5
5.1.6
5.1.7
5.1.8
5.1.9
5.1.10
5.1.11
5.1.12
5.1.13
5.1.14
5.1.15
5.1.16
5.1.17
5.2
5.2.1
5.2.2
5.2.3
4P Theory ofOperation ....... .. ........................................ .. .. ...... .. 21
CPU Theory ofOperation 23
Introduction. .................................................................... .. 23
ResetCircuit ..................................................... .. 23
CPU............................................................................ 23
SystemTiming. .............................................................. 23
AddressDecode ........... .. ...................... .. ............ .. .. .. .. . . . . . . . ... 26
ROM....................................................................... 26
RAM 37
VideoCircuit 51
Keyboard .. ............................ .. ................ .. ..................... .. 53
Real TimeClock ............................... .. ...... .. .. ...................... .. 53
LinePrinterPort. ..... .. ........ .. .............. .. ...... .. ........................ .. 53
GraphicsPort. ................................................................... .. 57
Sound 57
I/OBusPort 57
FDCCircuit 59
RS-232CCircuit 64
Troubleshooting (specific) 66
Schematic8000192 ............................................................... 67
PCBArt(1700254) 75
Parts List, PCB Assembly ............................................... .. 79
4P Gate Array Theory of Operation ..... .. .... .. .................................. .. .. 85
CPU Theory of Operation 85
Introduction. ................................................................. 85
ResetCircuit ............................................. .. 85
C~ ···· ·····85

5.2.4
5.2.5
5.2.6
5.2.7
5.2.8
5.2.9
5.2.10
5.2.11
5.2.12
5.2.13
5.2.14
5.2.15
5.2.16
5.2.17
5.3
5.4
5.4.1
5.4.2
5.4.3
5.4.4
5.4.5
5.4.6
5.4.7
5.5
5.5.1
5.5.2
5.5.3
5.6
5.6.1
SECTION VI
ADDENDA
A.
SystemTiming. .................................................................. .. 85
_AddressDecode ....... .. ........ .. ...... .. ........ .. ........................... 87
ROM 87
RAM 98
VideoCircuit 112
Keyboard .......................................................................
.. 114
RealTime Clock .........
.. .......................... .. ............... .. ......... .. 114
Line PrinterPort _........................................
.. .. . . .. 114
GraphicsPort 118
Sound 118
110 Bus Port 118
FDCCircuit 120
RS-232CCircuit 124
Troubleshooting(specific) 126
Schematic8000192 _127
PCBArt (1700254) _134
Parts List, PCB Assembly .....
.. ..... .. .......................... .. . .. 137
Mini-Disk Drives
(Tan don TM-50) 143
PowerSupplyAssembly 143
PowerSupply Description ..................
.. .... .. ............................ .. . .. 143
Technical Specifications 147
TheoryofOperation ..............................................................
.. 148
TroubleshootingChart _...............................................
.. 158
Testingand Adjustments _ " 159
Schematic 8000164, 65W Power Supply 8790049
161
Component Layout, 65W Power Supply 8790049 ..................................... .. 163
Circuit Trace, 65W Power Supply 8790049 ...........................................
.. 164
Parts List, 65W Power Supply 8790049 _ " 165
CRTDisplay
_........ . _ 169
Specifications _169
Adjustmentprocedures _
171
TheoryofOperation .............................................................. .. 174
Schematic 23533 (BIW) and 23757 (Green) 179
Parts list 8790612 (BIW) and 8790613 (Green)
181
Options 189
GraphicsBoard 189
Exploded View/Parts
Lists. ....... . 199
CaseAssembly .202
Main ChassisAssembly _ _ _ 204
DiskDrive Assembly 206
KeyboardAssembly _. . _ 208
Tandon Operating and Service Manual, TM50-1 and TM50-2 5-1/4" Flexible Disk Drives

MODEL 4P/4P GATE ARRAY
HARDWARE
SECTION I
INTRODUCTION

INTRODUCTION
1.1 SYSTEM OVERVIEW
The TRS-SO Model4P Microcomputer is acomplete, self-con-
tained portable (transportable) version of the popular
TRS-SO
Model 4Microcomputer. It provides acarrying/protective case
which has a recessed carrying handle, removable front cover
which protects the CRT and disk drives and serves as abase
when in the portable configuration, and self-contained key-
board conveniently stowed away in a recess in the main case.
Power cord, floppy disk and manual storage are provided in-
side the removable cover/base. All connections to peripheral
equipment are made at the rear of the Model 4P and optional
feature connections are made by removing a rear cover plate.
Proper care and handling must be observed to prevent damage
to the computer.
3
The Model 4P is 100% compatible with all Model III and Model
4disk software. System capability for Model III compatibility in-
cludes:
ZSOA CPU, 2MHz operation, programmable RAM to
emulate ROM lor BASIC operating system, memory-mapped
keyboard, memory-mapped video with 64-character by 16-line
display, and full
4SK Random Access Memory (RAM). Model 4
compatibility includes:
ZSOA CPU, 4MHz operation, memory-
mapped keyboard
in upper memory, memory-mapped video in
upper memory with SO-character by 24-line display, standard
64K
RAM expandable to 12SK RAM. Other standard teatures
of the Model4P which were options on the Model
III and Model
4are built-in FDC Circuit with two
lS4K Floppy Disk Drives and
an RS-232-C Serial Communications Interface Circuit.
1.2 OPTIONAL FEATURES
Optional features available on the Model 4P include: 640 by
240 pixel High Resolution graphics Board, Direct-connect,
auto-dial, auto-answer 300 bps Modem Board. The Model 4P
does not support cassette operation
or external Floppy Disk
Drive.

TOP COVER/POWER SUPPLY
CASE
CRT
SWEEP
BOARD
~
,
~
l!! "
:::>
Dl
ii:
REAR
MOUNTING
PLATE
DISK
DRIVE
ASSEMBLY
,~
~
PAN/MAIN
LOGIC PCB
KEYBOARD
11
1'l/$
CONTROL ," lJ
MODULE ~~j'" Uo
1>1
~~MAIN
CHASSIS
FRONT
BEZEL
~"
COVER/BASE

1.3 SYSTEM BLOCK DIAGRAM
The System Block Diagram (Figure 1.2) shows the various internal components and connections of the Model 4P
Microcomputer.
#1
FLOPPY
DISK
DRIVE
8790121
CONNECT TO
RS-232-c
SERIAL
PORT
FOC CABLE
#8709457
#0
8790121
FLOPPY
DISK
DRIVE
#8709456
DC FAN
*8790406
#8709460
DC HARNESS
RS-232-C
SERIAL
PORT
I/O
BUS
PORT
KEYBOARD CABLE
RESET SWITCH
CABLE
#8709457
E1
#87D
70-KEY KEYBOARD
iB790530
[J
~~8~~OT ROM
64K OR 128K RAM
REAL TIME .. __ ..
CLOCK VIDEO
INTERFACE
HI -RES KEYBOARD INT.
GRAPHICS LINE PRINTER INT.
BOARD r/o PORT INT.
(OPTIONAL) RS232-c SERIAL
INT. FLOPPY
DRIVE INT.
HI-RES GRAPHICS
BOARD INT.
#8709427
LINE
PRINTER
PORT
RESET
SWITCH
8489071
#8709455
CRT PC
BOARD
iB790612
CONTRAST
CONTROL
#8261150
POWER
SUPPLY
#8790049
POWER CORD
#8709475
50---4'
VIDEO HARNESS
#8709452
BRIGHTNESS
CONTROL
#8262450
Figure 1-2. Model 4P Block Diagram
5

SECTION II
SPECIFICATIONS
7

SPECIFICATIONS
2.1 MICROPROCESSOR: 4MHz Z80A, 8-bit CPU
Memory:
Keyboard:
Video Display:
Floppy Disk Drives:
64K RAM bytes, expandable
to 128K bytes 4K boot ROM, 2K video memory
70-key standard typewnter keyboard, including 12-key numeric entry keypad. Special keys include
BREAK, CTRL, CAPS, CLEAR, plus three programmable special function keys (F1, F2, and F3).
High-resolution
9" black and white display monitor with 64 or 32 characters per line by 16 lines in
Model III mode and 80 or 40 characters per line by 24 lines in Model 4/4P mode. Displays upper
and lowercase ASCII characters, with descenders, 96 special characters, 64 alternate characters,
64 graphics characters, plus reverse video of
all ASCII alpha-numeric characters.
Two built-in single-sided, double-density
5-114" thin-line floppy disk drives. Each drive stores up to
184K bytes. Data transfer rate
is 250K bits per second.
2.2 PERIPHERAL INTERFACES
Standard:
Optional:
I/O BUS for connection of hard disk and other peripherals.
Serial Interface (RS-232-C port) One RS-232-C Serial Communications Interface port which allows
asynchronous and synchronous transmission. Mates with 08-25 connector on back of the Model
4P.
Parallel Printer Interface Connection to a line printer via the 34-pin connector on the back of the
Model4P.
640 x240 High-Resolution graphics board
Auto-answer Modem (300 baud)
2.3 POWER REQUIREMENTS
105-130 Vac, 60 Hz
240 Vac, 50 Hz (Australian)
220 Vac, 50 Hz (European)
Grounded Outlet
Maximum Current Drain: 1.7 Amperes
Typical Current Drain: 1.5 Amperes
2.4 OPERATING TEMPERATURE: 55 to 800F(13 to 2T C)
2.5 DIMENSIONS: 9.3" H x 16.5" W x 13.25" D, 261bs carrying weight.
9