Tandy 2000 User manual

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TANDY@ MODEL 2ggg COMPTTTER
Copyright 1984 Tandy Corporation
A11 Rights Reserved
Reproduction or use, without express written permission from
Tandy Corporation, or 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 t oy from the use of the
information contained herein.

Tandy@ Model zfigg Service Manual
Table Of Contents
Introduction
Specifications ...., 7
.1 Physical Characteristics 7
.2 System Operating Characteristics 7
.3 Peripheral Interfaces 7
.4 Optional Features I
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2
2
2
2
2
3
3
3
3
3
3
.1
.1
.l
.2
.3
7.1.1
-l .L.2
7.1.3
7 .L.4
7 .L.4
7 .L.4
7 .L.4
7.1.5
7 .L.6
7 .L.7
7.1.8
7.1.9
General
Disassenbly,/assenbly ..... ........
Main Unit
.1 Power Supp1y orrro
.2 Disk Drives
Keyboard Assembly
Display Unit
9
9
Lg
11
L2
13
39
39
39
41
42
43
43
q/ Adjustments . 15
4.L Power Supply 15
4.2 PLL Adjustment 15
4.3 Video Adjustment.. 15
S/ Cabling Diagram,/Pinout Connections 17
5 Troubleshooting Procedures
6. I Power Supply
6.2 Other Components
7/ Theory of Operation
Block Diagram
7 .L Main Logic Board
CPU 44
Bus Interface ...:. Sfi
video System 58
.1 Video System Theory Of Operation 69
.2 Address Control Register 63
.3 Character Attributes Byte 64
Character Generator 66
Boot ROM/Interrupt Controller 68
Clock/Pr,r, 72
timing and Control Circuits 77
.1 l'lemory Control Overview 77
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Tandyo Model zgflg Service l{anual
Table Of Contents
7.L.8.2 Memory Timing Circuit
7.1.8.3 Parity Testing
7 .L. 8 . 4 Ref resh Control
7.1.8 .5 Memory Control
77
79
8g
81
83
83
83
85
85
86
89
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efl
91
92
92
94
95
96
96
97
98
ryL
L27
133
r43
143
L44
r46
L52
rs 3
15r
163
165
171
7 .L.9 Floppy Disk Controll
7 .L.9.1 Data Bus Interf ace
7 .L.9.2 FDC Port Specif ica
7 .L.9.3 DMA Request and Ac
7 .L .9 .4 FDD Read Data Sequ
7 .L.9.5 FDD Write Data Seq
7 .L.9.6 FDC/ FDD Interf ace
7 .L .9 .7 Drive Select Decod
7 .L. 9 . 8 READ/WnrrE and SEE
7 .L. 9 . 9 FDC Reset Control
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7 .I.Ig Parallel,/xeyboard Interf ace
7 .L.Lg .L Printer Port
7.L.L9.2 Keyboard Interf ace
7 .I .IF .Z Revi s ion Port
7.1.11 Serial Interface/Programmable Timer
7 .L.11.1 Serial Interface
7 .L.IL.2 Counter/Timer Chip
7.1.11.3 RS-232 operation
Schematic 8ggg2{3, Main Logic Board
Component Layout/Ckt Trace L7gg245
Parts l,ist, Main Logic PCB
7.2 Power Supplies
t"lai n Power Supply ( 95 W)
Technical Specifications o.,,..... o. o r...,.
Troubleshooting The Power Supply ...o.oo.oo
7 .2.I.3 Perf ormance Test
7.2.I.4 System Description
Schematic 8ggg2L3 | 95W Power Supply
Component Layout L79fl259, 95W Power
Parts Li st
7.2.2 Auxiliary Power Supply
7 .2.L
7 .2.1. r
7 .2.L.2
(38W, Hard Oisk Drive OnIy)
7.2.2.L Troubleshooting The Power Supply L7I
Schematic, 38W Power Supply 8799925 . L77
7.2.2.2 Parts List L79
Supply .....rr.i

Tandyo Model zfigg Service llanual
7.3 Disk Drives
7 .3.I Floppy oisk Drive
7 .3.2 Hard Disk Drive
7 .3.3 Hard Oisk Controller PCB
7.3.3.1 Port Decoding
7 .3.3.2 Drive Control
7.3.3 .3 Data Recovery
7 .3.3.4 Controller Alignment
7.3.3.5 HDC Register Specifications ..........
Schematic |fltfrzflL
Component Layout L799258, Hard oisk Control1er......
Parts List
7.4 Motherboard
Schematic SgggZI2
Component Layout 17gg246
Parts List
7 .5 12 8K RAM Board ( Schematic 8ggg2g 4)
8/ Parts Lists/Pxploded Views
Main Logic Unit Assembly
Power Supply As sembly ( 95 W)
7.5.1 Introduction 2LL
7 .5.2 Theory of Operation 2LL
7.5.3 Signal Definition 2Ll-
7.5.4 Troubleshooting 2l-2
Schematic 8ggg294 2L7
Component Layout L7gg258 2l-9
7.5 Keyboard Assembly 223
7 .5.L Keyboard Specifications . 224
7.6.2 Key Code Chart 225
7 .6.3 Keyboard Timing 227
7.6.4 Keyboard Layout 228
r83
183
r83
183
184
184
18s
L87
r88
191
19s
L99
zfit
2gs
297
2Lg
2LL
23r
232
234
Disk Drive Assemblies 236
Card Cage Assembly 238
Keyboard Assembly 249
Display unit 242
g/ Optional Features
9.1 Internal l28K Expansion RAM 243
Schematic 8ggg2g5, 128K Expansion RAt"l 247
Component Layout 1-799252, 128K Expansion RAIVI 249
9.2 External Memory Board 252
Logic . r . r . . . . . . . . o . o . r . o r . . .
arl
L11

l' - , rll-q--I- ---4 lL- ltLl
Tandy@ Model 2ggg Service lr{anual
Schematic 89fl92l8, I28/256K External RAM 263
Component Layout, I28/255K External RAM 257
Parts List, 256K Board with 128K RAM Installed 272
9.3 Hi-Resolution Graphics Option
Schematic 8gggL95, Hi-Res Graphics 283
Component Location 179926L. ni-Res Graphics 287
Parts List, Hi-Res Graphics PCB Assembly 889BgLg 292
Appendices
A/ Service lv1anual - Mitsubishi Floppy Disk Drive 4853
Service lvlanual - l,litsubishi Floppy Disk Drive 4853-1
B/ Service lulanual - Tandon Hard Disk Drive
C/ Intel Corporation Specification Sheets
iAPX186 8259 82s1 8fr87 8253 82s3
8272
D/ Standard lvticrosystems Corporation
Specification Sheets
9997 92L2 9fi2r 9216E
E/ Model 2ggg port Specifications
I
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Tandy@ Model 2000
rl t I
Service l.Ianua1
Fig. No.
L.I
L.2
1.3
7 .L
7.la
7.2
7 .3
7.4
7.5
-l .5
7 .7
7 .8
7 .9
7. r0
7.1r
7/L2
7. 13
7.L4
7 . 15
7. 15
7 .L7
7.18
7 .L9
7 .20
7 .2L
7 .22
7 .23
7.24
7 .25
7 .26
7 .27
7 .28
7 .29
7 .30
7. 3l
7 .32
Lis t of Figures
Descr iption Page No.
Ivlodel 2000 Computer Assembly .. o...... o . 2
llodel 2000 Major Copmponent Subassemblies 3
External Plug-in Option Cards ,...o-r.,. 6
I,Iodel 20C0 Functional Block Diagram .o.o 42
CPU Block Diagram .......... ,............ 45
80186 Progfalnmed Chip SeleCtS o......... 46
Peripheral Chip Select 0 Address oo.,... 47
Dl,lA Acknowledge Address Assignments r.,. 47
DMA Channel COntfOl REgiStef ....oo..oo. 49
Bus Interfacg Block Oiagram ..-......... 51
timing Par€rmetgr Diagram o.............. 57
CRT Controller/Ivlain Video Logic ........ 59
Charactgr Ggnerator ., o. . r..,. o o.,.,.. r. 67
Intefrupt COntfOllef /gOOt ROIt{ ..r...,o.o 59
Interrupt Controller Register Assignments 7 0
InLerrubt Controller Input Assignments . 7L
Block Diagram, CIock/pLL ..,. o......... . 72
Block Diagramt CIock/pLL (sheet 8) .r.,. 73
MOdeI 2000 PLL BIOCk Diagfam ... o.. r... . '1 4
Mgmory Timing and Control .rorr,,,o...r. 78
RAM Controller IFL Output Definitions o. 79
Floppy Disk Controllgr ...... ........... 84
FIt{ EncOding Scheme ..............,'..... . 87
MFII{ EncOding Schgme ....,r..... r.... r r.. . 87
Ser ial Inter f ac e/ Programmable Timer r . o o I I
ParalleL/xeyboard Interface .... o. o.. o.. 93
Load Box . r. r.... o. o o...... r r......... t. L47
Load Box Assgmbly ... r.......... o. o..... L47
Tgst Circuit . f... r. o o...... o.. f....... r I48
Wavgform .... o..... o..... o..... r. o...... 148
Test Equipment Sgtup ..oo.......o..o.... I49
Base of Q15 .r.ro..o.o..ror........orr.f 150
Q15 Collector Waveform ................. 151
Wavgform of U3, Pin 8 .................. 151
Chip Oscillator, Pin 5 ...... .. o... e ... . L52
Basic Flyback Convgrter .....oo.r....o.. I53
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Tandy@ Model 2000 Service tlanual.
7.33
7/3q
7.35
7 .35
7 .37
7.38
7 .39
7 .40
7 .4L
7.42
9.1
9.2
9.3
9.4
9.5
List of Figures
Waveforms for Figure 7.32
Block Diagram I o r . | . o e o r r | | . | | o r . o I o . o .
Tgst Sgtup rf f . r rr..... r.ro ro.... ooorf f
Q2 Co1lector Wavgform . . . . . . . . . . . . . . r . .
QZ Base Waveform .......... r.. o.. - -... -
Powgr pin Assignments . o . . . . . . . . . . . . . . r
Keyboard Assembly Connector . . . . . ., o o . .
Keyboard Assembly Timing Chart o....,.r
Kgyboard Identification . . . . . r . . . o . . r . o
Key Number Identification .,.... o. . r...
Block Diagram, External Memory Board ..
Board Select f.......... o o.. o....... o..
Memory Control Block Diagram .,oo..oor,
Normal Cycle PIus Refresh Cycle .,,o.oo
U42 Diagrarn ............ o.... r... r... o.
15 4
rs 6
L72
L74
L74
L7s
223
227
228
228
258
259
260
25L
262
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Tandy@ Model 2000 Service lvlanual
L/ Introduction
The Radio Shack I'lodel 2000 Personal Computer is modular in
design to allow maximum flexibility in system configuration.
The basic computer consists of a lvlain Unit, a detached
keyboard with coiled cable for positioning the keyboard in
the most convenient location, and a monitor. The lv1ain Unit
may be supplied with two internal floppy disk drives or one
floppy disk drive and one internal hard disk drive. The
standard monitor used with the Model 2000 is a monochrome
displ-ay (green phosphor) which has a standard screen format
of 80 characters width and 25 lines vertical. Since this
unit is modular, it may be placed on top of the Main Unit or
at any location convenient to the operator.
Internal floppy diskette storage is provided by either one
or two 5-I/4" floppy disk drives. If the unit is supplied
with two of these units, total internal memory storage
capacity is L.46 l4bytes. When supplied with the internal
hard disk and one floppy disk storage unit, total internal
memory storage becomes 10.73 Ivlbytes.
An optional Color l'lonitor may be used with the Model 2000 to
provide up to eight of sixteen different colors on the
screen at one time. This optional feature requires the use
of a color monitor PCB assembly which plugs into one of the
mother board slots at the rear of the Main Unit.
An internal 128K RAt't board is standard on the Model 2000.
An option to the Model 2000 is an additional 128K RAM board
which provides expansion to 256K. Both boards are mounted
internal to the Main Unit. An additional optional feature
is a 256K RAM board which connects to the internal
motherboard of the lt{ain Unit. It is populated with 128K RAM
which may be expanded to 256K RAf',[ with the addition of RAM
ICs. Two of these boards can be installed into the
motherboard in the unit's card cage assembly. With aII
these options installed, the Model 2000 then has internal
RAM memory capacity of 758K bytes.
Other options include a IY/Joystick input, a mouse/cl-ock
option which aIlows input from a hand-positioned interface,
a monitor pedestal, black and white graphics option, and a
f loor unit which mounts the l"lain Unit vertically.
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Tandy@ Model 2000 Service Manual
Figure I.1 Model 2000 Computer Assembly
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Tandy@ Model 2000 Service tlanual
CARD CAGE
COVER STRIP
VIDEO
( B -PIN FEI\,IALE
REAR VIEW
OUT
DIN )
FUSED TO MONITOR
FUSED IN
CARD CAGE ASSEMBLY
(4 CARD)
MOTHERBOARD
CONNECTORS ( 4 )
FLOPPY DISK DRIVES
RS 23 2 OUTPUT CONNECTOR
PARALLEL PRINTER (MALE )
TOP VIEW
3BW PS
FOR HARD
DISK
95W PS
HARD DISK I4OUNTING AREA
Figure I.2 Model 2000 Ivlajor Component Subassemblies
FAN
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Tandy@ Model 2000 Service t'lanual
The Main Unit is the heart of the Radio Shack Model 2000
microcomputer. It houses the microprocessor, Read-Only
l'lemory (ROM - 15K for system start-up), system power supply,
RAM boards and expansion slots for optional features, floppy
disk drives (either one or two), and the internal hard disk
drive and power supply.
The ltain Logic Assembly is a large board mounted to the
bottom of the lvlain unit and interconnected to the keyboard,
povrer supply, motherboard, and disk drives by a series of
cables. A system block diagram is shown in Figure 1-1
showing the major components of the Model 2000 and the
interconnecting cables. Both standard and optional features
are included in this figure to provide a complete overall
interconnection diagram of the unit.
The standard Power Supply for the lrlodel 2000 microcomputer
is a 95W switching regulator type, designed to provide
adequate capacity for most all add-on features of the
computer. When the system is supplied with the hard disk
option, however, an additional 38W power supply is required
to power the hard disk assembly separately.
The Model 2000 has a detachable keyboard which is connected
to the Main Unit with a lightweight coiled cable which
allows the keyboard to be used up to 3 feet away from the
Main Unit for operator convenience. The keyboard features
90 keys in a standard typewriter keyboard layout with
additional keys for numbers and functions.
The Floppy Diskette Drive uses special 5-L/4" double-sided,
double-density diskettes to read, write or store data.
These are 96 TPI soft sector diskettes. Two Disk Drive
assemblies are installed in the standard unit r or it may
contain one floppy disk drive and one internal hard disk
drive assembly. Each of the floppy diskettes stores
approximately 730 Kbytes of data. The hard disk drive is
capable of storing 10 Mbytes of data. A11 system programs,
with the exception of the system startup sequence, are
stored on diskette.
The monitor used on the Radio Shack t'lodel 2000 may be either
a monochrome (#26-51ff) or color (#26-5J-12) display. The
monochrome monitor is a high resolution green phosphor
display which provides excellent visual quality. It
features a L2" screen with an anti-glare surface for
improved viewing. The display is 25 lines of 80 characters
each with the capability of displaying 256 ALfferent letters
or characters. The characters are formed using a 7 x 9
matrix dot pattern.
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Tandy@ Model 2000 Service l-lanual
Also available as an enhancement of the black and white
monitor is a e/w graphics option board (26-5L4O). This
feature al-J-ows the presentation of graphic material on the
display monitor with individually addressed pixels. A color
monitor (26-5LI2) is available which utilizes a 14" color
screen, a color graphics option (25-26-5141), and the B/w
graphics option to provide 8 color presentations at one time
on the monitor.
Standard internal RAIvI memory consists of a plug-in 128K
board. This board plugs into the Main Logic board and may
be expanded to provide 256K of RAM with an additional 128K
board (26-5160). In addition to this memory up to two
26-5L6L boards (considered external since they are
accessible from the outside of the ltain Unit) may be plugged
into the motherboard located at the rear of the Main Unit.
These boards are populated with 128K of RAM and may be
further expanded to 255K each with additional 54K x I RAM
chips (option 26-5L62). When all of these boards are
incorporated into the system, they provide a total RAIII
capacity of 784K bytes of memory.
The TV/Joystick Board allows attachment of user-supplied Joy
Sticks or paddles. Two joysticks may be attached to t,he
ltodel 2000 for use with games available in the software
library of the Model 2000.
The I'1ouse,/C1ock option board allows input with an external
input device called a "mouse" as well as providing the time
of day with a battery backup clock,/calendar chip. The mouse
is a unit which is rolled along a desk top and encodes a
digital input to the computer.
A built-in RS-232 asynchronous interface allows
communication with external devices through the use of a
modem. These devices may be local or remote, using a
telephone line to co'm0unicate. The option supports 50 to
9500 BPS transmission speeds and utilizes a 25-pin D
connector located on the rear panel of the Main Unit.
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Tandy@ Model 2000 Service l{anual
Ivlonoc hrome
Graph i c s
Board Color MONITOR Connector
Figure I.3 External Plug-in Option Cards
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Tandy@ ModeJ- 20OO Service lianua].
2/ Specifications
2 .L Phys ical Characteristics
Main Unit
Width 19.0 inches
Height 6.0 inches
Depth 16.0 inches
48 .26 cm )
L5.24 cm)
40.64 crn)
Weight
25-5103 23.0 Pounds (10.4 kgm)
26-5L04 25.5 Pounds (12.0 kgm)
l"lonochr ome lvlon i tor
width L6.25 inches (4L.28 cm)
Height 11.4 inches (29.0 cm)
Depth L2.2 inches (31.0 cm)
Weight 15.4 pounds (7.0 kgm)
Keyboard
width L6.25 inches (4l-.28 cm)
Height L.2 inches (3.05 cm)
Depth 7.875 inches (20.0 cm)
Weight 2.8 pounds (1.3 kgm)
2.2 System Operating Characteristics
Storage Temperature -40 to +160oF (-40 to 71'C)
embient Temperature 55 to 95oF Q2 to 35oC)
Voltage Range (USA) 95 to 135 Vac
(Europe) - 190 to 270 Yac
Current Drain - USA - AC lvlain Unit,/Convenience Outlet
Model 25-5103 3.0 AmPeres
Model 25-5L04 3.5 AmPeres
European - AC current lv1ain Unit only
l4ode1 25-5103 0.94 AmPere
l'lodel 26-5L04 - L.2 Amperes
Line Frequency 47 to 63 Hz
2.3 Peripheral Interfaces
RS232C Connector - DB25 socket connector accessible at
the rear of the main unit. Pinout connections are
shown in Section 5 of this manual.
7

Tandy@ Model 2000 Service Flanual
2.3 Peripheral Interfaces (con't)
Parallel Printer Connector 34-pin connector for
connection of parallel printer or modem for
conversion to serial transmission. Pinout
connections are shown in Section 5 of this manual.
Ivlonochrome l'lonitor Connector 8-pin socket DIN
connector accessible at the rear of the lrlain Unit.
Motherboard accessible from the rear of the Main Unit
allows up to four optional boards to be plugged
into main unit. Existing cover strip and NyJ-atch
latches are removed and optional board is inserted
and latched into place with t',tylatch hardware.
2.4 Optional Features
Internal 128K RAlrl Board plugs into existing 128K RAM
board to give 256K bytes of internal RAII{ storage.
Requires disassembty of the main unit for
installation. See Section 2 on disassembly
procedures.
External 256K Board - plugs into slot on Motherboard at
rear of main unit. Supplied with 128K, but may
have another 128K added for total of 256K bytes of
external RAl4.
TV/Joystick Board plugs into slot on Motherboard and
allows use of Joysticks for games available in
software library of Model 2000.
It{ouse/Clock Option Board - plugs into slot on
Mother-board. Provides real time clock displayed
on monitor screen as well as input from external
"mouse" option, a hand-positioned transducer which
translates rrxrr and rrYrr position into digital
encoded signal.
8

Tandyo Model 2000 Service lrlanual
l/ Disassenbly/Rssenbly
Since the Model 2000 is modular in its construction,
disassembly,/assembly procedures are simplified. The main
modules which make up the Model 2000 are the Main Unit, the
keyboard, and the display monitor. These three units may be
supplemented by various I/0 devices such as printers,
modems, memory devices or additional monitors. Disassembly
of each module will be described in the following
paragraphs. Exercise case when handling the modules to
prevent damage to internal components or exterior surfaces.
3.1 Main Unit
The Main Unit contains the Power ON-OFF swit.ch and
indicator, the disk drives and the system power supply. AII
cables interconnect this unit with external devices. Most
cables are connected to the rear terminal panel of the lrlain
Unit but there are some connections to the front panel of
the Main Unit, such as the keyboard connector. Attached to
the bottom of the main unit is a metal chassis which houses
the main logic PCB assembly. Turn the Main Unit assembly on
either the left or right side to gain access to the mounting
screws. There are four screlrs which attach this assembly to
the l4ain Unit housing. When properly positioned, the logic
board provides interconnection from this base pCB to the
Mother Board which is used for interconnecting optional
feature boards. In addition to this 95-pin connector, there
are other connectors which tie to t,he PCB. When the screws
are removed from the base cover, swing the rear of the cover
away from the main unit. This will allow the connectors
which are at the front of the unit to be removed without
damaging them.
Disconnect all connect,ions to the main logic PCB (these
include the power input, reset, and sound). With these
connectors disconnected, the base assembly may be removed
completely from the Main Unit assembly. The PCB is attached
to the metal base assembly with nine screws. There is an
insulating separator to prevent possible shorting of any of
the components on the PCB to the metal base assembly.
The Main Unit housing contains the Power Supply, the Disk
Drive Assemblies (either two floppy disk drives or I floppy
and I hard disk drive) and the Motherboard for system
options. To gain access to the interior of this unit,
remove two mounting screws at t,he lower rear of the I'tain
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Tandy@ Model 2000 Service Flanual
Unit. After removing these two screws, slide the top cover
forward to release the catches at the front, then lift the
top cover off the assembly. The back panel portion of the
case housing remains a part of the Main Unit base as well as
the power swj-tch/reset and indicator.
3 .1.1 Power Supply
The 95!! main power supply for the lrlodel 2000 is located at
the left side of the Main Unit and is accessible when the
cover is removed f rom the lvlain Unit as noted previously.
The power supply is attached to the base of the Main Unit
with 6 screws, 4 of which are screwed into the bottom of the
base and 2 of which are attached to the backside of the
front bezel If the Main Unit has a Hard Disk assembly
installed, it must be detached to provide access to the
connectors which connect the power supply to the Main Logic
PCB.
t. Remove the connectors attached to the lrtotherboard, d,isk
drives, and l{ain Logic PCB.
2. Remove 4 screws which attach the power supply assembly
to the base plastic.
3. Remove the two screws which connect the power supply to
the front bezel assembly.
4. Lift the power supply from the Main Unit.
5. Remove 3 screws from the RH side of the power supply to
allow the upper enclosure to be lifted off the supply.
6. Remove 4 connectors which attach to the power supply
PCB.
7. Remove 8 screws which attach the PCB to the lower
enclosure weldment.
8. Cable replacement is accomplished by removing the
connectors from the enclosure wel-dment. AIl connectors
are clip-mounting type connectors which a1low
replacement without special tools. Remove wires
attached to the connector and then depress retaining
clips from inside the enclosure. S1ide connector out
of enclosure weldment.
10

Tandy@ Model 2000 Service Manua1
Assemble the power supply in the reverse order of
disassembly. Ensure that the power supply is properly
operating before reinstalling it in the lvlain Unit. See
Section 7.2 for checkout procedures for the main power
supply.
The 38W Hard Disk power supply assembly is attached to the
underside of the power supply cover and nests above the main
power supply PCB. It is accessible when the cover is
removed from the main supply.
1. Remove the cover from the main unit as noted in
Paragraph 3.1.
2. Remove the main power supply cover by removing the 4
mounting screws.
3. Remove the mating connectors to the 38W power supply
there are two connectors. One is for AC input and
the other for DC output. There are three DC output
connectors on the PCB. The DC output connector may be
attached to any one of the three on reassembly.
4. Remove the 38W power supply board from the cover by
removing the 4 mounting screws.
Reassembly of the power supply is in the reverse order of
disassembly. Ensure that the orientation of the supply is
the same as it was prior to disassembly to prevent
interference with the main power supply PCB components.
3 .L.2 Disk Drives
The floppy disk drives are mounted at the right side of the
Ivlain Unit, attached to the base of the main unit with a
mounting bracket on either side of the drives. The drive
assemblies ( including mounting brackets ) may be removed from
the Main Unit base by removing 4 screws in the base. After
these screws and cables connected to the drives are removed,
the drive assembly may be removed completely from the Ivlain
Unit.
The hard disk assembly is mounted to the left of the floppy
disk drive assemblies. If the unit contains a hard disk
drive assembly, it is removed from the Main unit by removing
the four mounting screws and attached cables.
11