Radio Shack TRS-8O User manual

!ladleIhaeK
•
ervlce
TRS-BO®
DISK/VIDEO INTERFACE
[AND EXPANSION FLOPPY DISK DRIVE UNIT)
•
l'•
1
,
Catalog Numbers: 26-3806/3807
.. .;-: '"
CUSTOM MANUFACTURED FOR RADIO SHACK. ADIVISION OF TANDY CORPORATION

"ill
Contents
1IINTRODUCTION 1-1
GENERAL. ........•..........................................••..1-1
SYSTEM OVERVIEW ..•.....................••........•••........•...
1-2
SPECIFICATIONS ........................••..........•..............1-4
2/DISASSEMBLY INSTRUCTIONS. ................................ .. 2-1
TOP CASE .................................•••........••......... 2-1
MAIN P.C. BOARD
...........................•.........•.•........... 2-1
POWER SUPPLY P.C. BOARD
......•..................•.•.........•...... 2-1
DISK DRIVE UNIT
..................•••.........••.................•. 2-2
FRONT PANEL ASSEMBLY ...........•.................................. 2-2
3/PREVENTIVE MAINTENANCE .................................. .. 3-1
ADJUSTMENT ....•..............................•.•.......•....... 3-1
SYSTEM CLOCK
........••...................................... 3-1
POWER SUPPLY
3-2
4/THEORY OF OPERATION. ..................................... .. 4-1
CPU ...........................•.........••........•.........•.. 4-2
ADDRESS DECODING AND BANK SELECTION CIRCUIT 4-3
MEMORY MAP ....•...............................•................ 4-3
I/O MAP .....•.........•..........••.........•........••......... 4-4
CLOCK GENERATOR CIRCUIT 4-5
SYSTEM BUS INTERFACE CIRCUIT
...........•••........••.........•...... 4-6
CRT INTERFACE AND CONTROL CIRCUIT 4-8
FLICKER SUPPRESSING CIRCUIT .................•••.................••.4-11
FDD INTERFACE SIGNALS ........•............•..................••.. 4-11
FDD CONTROL CIRCUIT. .........•................................... 4-13
POWER SUPPLY AND RESET CIRCUIT ............................••....... 4-16
5/TROUBLESHOOTING .......................................... .. 5-1
TROUBLESHOOTING FLOWCHART .....•.................................. 5-1
CHECKING PROCEDURE
....................•..........•........•...... 5-2
6/EXPLODED VIEW AND PARTS LIST. 6-1
EXPLODED VIEW •.................................................. 6-1
ELECTRICAL PARTS LIST
6-2
MECHANICAL/ASSEMBLY PARTS. ...............••...................... 6-13
7/P.C. BOARD VIEWS AND SCHEMATIC DIAGRAM 7-1
MAIN P.C. BOARD , ......•...... 7-1
MAIN P.C. BOARD -- REVISED
.••..........•........••................... 7-3
POWER SUPPLY P.C. BOARD ...............................••........... 7-5
SCHEMATIC DIAGRAM ....................••.........•..........•..... 7-6
APPENDIX AI INSTALLATION OF ADDITIONAL DISK DRIVE UNIT. A-1
APPENDIX B/CONNECTOR PIN ASSIGNMENTS. ................... .. B-1
SYSTEM BUS CONNECTOR B-1
RF MODULATOR ..............................••...................• B-2

APPENDIX C/SERVICING THE FDD UNIT" """"""""""""""""""""""""""" C-1
PART 1" MECHANICAL SECTION" """""""""""""""""""""""""""""""""""""""" C-1
1-1 INSTALLATION/REMOVAL OF COMPONENTS" """""_"""""""""""""""""""" C-1
1-2 ADJUSTMENT" """"""""""""""""""""""""""""""""""""""""""""""C-7
1-3 SPECIAL MAINTENANCE TOOLS" """"""" __ """_"""""""""""""""""""" C-15
1-4 MAINTENANCE" """""""""""""""""""""""""""""""""""""""""""" C-15
PART 2" ELECTRICAL SECTION" """""""""""""""_"""""""""""""""""""""""" C-1"7
2-1 GENERAL DESCRIPTION" """""" """"" """""" __ """"""" """""" """"""C-17
2-2 BLOCK DIAGRAM" """""""" __ """""""""""""""""" __ """"""""""""C-17
2-3 ELECTRICAL DIAGRAM" " __ """""""""""""""""""" __ """"""""""_""_ C-1 B
2-4 INDEPENDENT LSI CONRGURATION """"""""""""_""_•"""""""_""""."C-19
2-5 INPUT SIGNAL LINES (CPU TO FDD) " ..... " " " " " " " " " " " .. " " . " " " _" " _" " C-23
2-6 OUTPUT SIGNAL LINES (FDD TO CPU) """"""""""""""""""""""" •. " ... C-29
PART 3" CIRCUIT DlAGRAM_ """""".""""" """""" .. " .. """"""""""""""" C-33
PART 4" TROUBLESHOOTING" """"""""" .• __ """ __ """""""""""•""•" .. """"" C-35
4-1 PROCESSING SOFT ERRORS" " " " .. """_""""""""""_""""" .. " .. " " " " " C-35
4-2 FLOPPY DISK DRIVE FOR REPAIR" """"."""""""" __ "_""""""""""""""" C-36
4-3 TROUBLESHOOTING PROCEDURES" """""" .. " _" _" __ """""" .. """"" •• "C-37
PART 5" EXPLODED VIEW AND PARTS LIST. " . " " " . " " " . " " .. """"""" ... """"""""C-47
PART 6. SPECIAL MAINTENANCE TOOLS """"""""""."""""""""""""."""""""".C-57
Note: The expansion drive unit (Radio Shack Catalog Number 26-3807) is exactly the sameas the built-in drive unit
of the DiskNideo Interface. When servicing the 26-3807, refer to the drive unit portion of this service manual.
j,

List of Illustrations
FIGURE
NUMBER DESCRIPTiON PAGE
NUMBER
Disk Drive Removal .
Cable Connections .
Disk/Video Interface (Front View} . . . . . . . . . .
Disk/Video Interface (Rear View) . . . . . . . . . . . . . . . . . .
Top Case Removal .
Removal
of P.C. Board < ••••••••••••••••••••••••••••••••••••••••••••••••••
System BUS Connector .
RF
Modulator . . . . . . . . .
P.C. Board Removal .. . . . . . .
Clamp
Base BK and Clamp Arm KRemovals . . . . . . . . . . . . . . . . . .
Carrier
BK Removal .. . . . . . . .. . .
1- 2
1- 3
2- 1
2- 1
2- 2
3- 1
3- 2
4- 1
4- 2
4- 3
4- 4
4- 5
4- 6
4- 7
4- 9
4- 9
4-10
4-10
4-11
4-12
4-14
4-15
4-15
6- 1
7- 1
7- 2
7- 3
7- 4
7- 5
7- 5
7- 6
A- 1
A- 1
A- 2
8- 1
8- 2
C- 1
C- 2
C- 3
C- 4
C- 5
C- 6
C- 7
C- 8
C- 8
.............................................
Pulse Motor BK Removal
System
Clock Adjustment . .
+5V Adjustment. . . .. .< • • ••••••••••••••••••••••••••••••••••••••
Block Diagram .
CPU Control Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Address Decoding and
BANK Selector Circuit .
Memory Map. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clock Generator
Circuit. ........................................ . .
System
BUS Interface Block Diagram (Receive Mode). ..................... . .
System BUS Interface Block Diagram
{Transmit Mode} .
CRT Interface Block Diagram .
Display
Timing Chart (40 Characters Mode) . .
Display
Timing Chart (80 Characters Mode) . . . . . . . . . .
Waveform
of Video Signal . .
Flicker Suppression Circuit. . . . . . . . . . . . . . . . . . . . .
FDD Interface Block Diagram. . . . . . . . . . . . . . . . . . . .
Data
Separator. .................... . .
Pre-Compensation
Circuit. ........... . .
Wait
Control Circuit .
Exploded View . . . . . . . . . . . . . . . . . . .
Main
P.C. Board (Top View) . . . . . . . . . . . . .. . .
Main
P.C. Board (Bottom View) . . . . . . . . . . . . . . . . . . . . . . .
Main P.C. Board-Revised
(Top View) . . . . . . . . . . . . . . . . . . . . . .
Main P.C. Board-Revised
(Bottom View) .
Power
Supply P.C. Board (Top View) .
Power
Supply P.C. Board (Bottom View) . . . . . . . . . . . . . . . .. . . . . . . . . .
Schematic Diagram < • • • •
•••••••••••••••••••
Preparation on P.C.B. of FDD . . . . . . . . .
Installation of FDD .............. .... .. . .
Spindle
Motor KRemoval . .
Track Sensor Removal .
Index Sensor
Adjustment .
Winding
the Steel Belt .
Mounting the Belt Supporter .
H
1-2
2-1
2-2
2-3
3-1
3-2
4-1
4-2
4-3
4-4
4-5
4-6
4-7
4-8
4-9
4-10
4-11
4-12
4-13
4-14
4-15
4-16
6-1
7-1
7-2
7-3
7-4
7-5
7-6
7-7
A-l
A-2
A-3
8-1
8-2
C-l
C-2
C-3
C-4
C-5
C-6
C-7
C-8
C-9
•

FIGURE
NUMBER DESCRIPTION PAGE
NUMBER
C-lO
C-1l
C-12
C-13
C-14
C-15
C-16
c-n
C-18
C- 19
C-20
C-2l
C-22
C·23
C-24
C-25
C-26
C-27
C-28
C-29
C-30
C-31
C-32
C·33
C-34
C-35
C-36
C-37
C·38
C-39
CAD
C-41
C-42
C-43
C-44
CA5
CA6
C-47
Mounting the Pulse Motor K . 0 0 ••••••••••• 0 •••• 0
Tensioning the Belt. _0 ••••••• 0 •• 0 •• 0 •• 0 •••••
Confirmation of the Belt Gaps ... 0 0 ••••••••••• 0 •••••••••••••
Fixing the Track 00 Stopper .. 0 0 • • • • • • • 0 •••••• 0 0 ••••••••• 0 •• 0 ••••
Waveform of Index Pulse .. _0 ••••••••• 0 0 •••• 0 0 0 •••••
Waveform of Head Output . . . . ... 0 0 • • 0 •••• 0
Motor Speed Adjustment. 0 ••• 0 ••••• 0 0 •• 0 ••
Track 00 Adjustment .0 ••••••• 0 0 ••••••••••••
Interrupter Timing Chart ..... 0 0 •• 0 ••
Block Diagram 0..... 0 ••••• 0 •• 0 •••• 0 •••••••••• 0
Electrical Diagram ... 0 0 • • • • • 0 •••••••••••••••• 0 •• 0
Pin Configuration of Control LSI. 0 •••• 0 0 ••••••• 0
Block Diagram of Control LSI. 0 •••••
Pin Configuration of Read LSI 0 0 • • •••• 0 0 •••• 0 •••••••
Block Diagram of Read LSI 0 0 •• 0 • • 0 •••• 0 ••••••••• 0
Block Diagram of Drive"Select Circuit. . . . 0 •• 0 • • • • • 0 •••••
Side Select Circuit ... 0 0 •••••••••••• 0 ••• 0 • • • • • • • • • • • • • • • • 0 •• 0 •••
Head Positioning Circuit 0 0 ••••••• 0 •• 0 • 0 • • • • • 0 •••••••
Timing Chart for the Direction and Step Signal ... 0 0 •• 0 ••• 0 0 •••••
Write Circuit and Erase Circuit ..... 0 0 ••••••• 0 0 • • • • • • • ••••• 0
Timing Chart for Write Circuit
Timing Chart for Erase Circuit 0 _ • 0 • 0 ••
Data Recording Procedure 0 •••••
Motor ON Circuit 0 ••• 0 ••
Index Circuit
Waveform
of TP2-4 Pin .0
Track 00 Detection Circuit 0
Waveform of TP2-2Pin .
Write
Protect Circuit .... 0
Read Amplifier Circuit .. 0 ••••••• 0 ••••••• 0 0 • 0 •••• 0
Timing Chart for Read Amplifier Circuit _ .
Circuit Diagram
0..... • • 0 •••• 0 ••••••• 0
Test System Hook-up .0 ••••• 0 •••• 0 •••••
Exploded View of Main Unit ... 0 •••• 0 • 0 ••• 0
Exploded View of Clamp Base BK and Carrier A .. 0 • 0 ••••• 0 0 •••••••
Exploded View of Pulse Motor BK. .0 • • • • • 0 • • • • •• o. 0 ••••••
PoCo Board. . . . . 0 • 0 •• 0 0 _ • 0 ••• 0 0 •••• 0
Special Meintenance Tool. 0
c· 9
C· 9
C·10
C-l0
C-"
C-ll
C- 12
C- 13
C-14
c·n
C-18
C-19
C-20
C-22
C-22
C-23
C-23
C-24
C-25
C-26
C-26
C-27
C-27
C-28
C-29
C-29
C-29
C-30
C-3l
C·31
C-32
C-33
C-36
CA7
C-48
C·49
C-50
C-57

TABLE
NUMBER
List of Tables
DESCRIPTION PAGE
NUMBER
4-1 I/O Port Description 4· 4
4,2 Signals from the Portable Computer 4- 6
4-3 PPI Function Table 4- 7
4-4
Function of the Principal Signals _4- 8
4-5 FDG Function Table '4-13
4-6 Description of the Principal Terminals . . . . . . . . . . . . . . . . 4-13
B-1 System Bus Connector Pin Assignments .. ............ . S- 1
Col Pin Assignments of Control LSI. . . . . . . . . . . . . . . . . . . . . . . . . C-21

•
1/lntroduction
This manual is prepared for the TRS-80 Disk/Video Interface technicians working in the field or repair centers. The user
of this manual should be acquainted with Z-80 CPU, 8255 PPI (Programmable Peripheral Interface), HD6845S CRTe {CRT
Controller) and M5W1793·02P FDG (Floppy Disk Controller).
This manual consists of seven sections and three appendices:
•The Introduction gives general information on
the TRS"80 Disk/Video Interface such as specifications, s~itch functions,
etc.
•Section 1describes disassembly procedures.
•Section 2describes preventive maintenance and adjustment.
•Section 3describes general theory
of the TRS-80 Disk/Video Interface operation.
•Section 4describes how to troubleshoot
the TRS-80 DisklVideo Interface.
•Section 5provides aparts list and an exploded view
of the TRS·80 Disk/Video Interface.
•Section 6provides schematics,
P.C. board diagrams and silk screen view of the P,C. boards of the TRS-80 DisklVideo
Interface.
•Appendix Aprovides instructions for installing an additional disk drive unit.
•Appendix Bprovides technical information for connector signals.
•Appendix Cprovides service information on
the built-in FDD unit.
General
By utilizing the TRS-80 DisklVideo Interface with the TAS·80 Portable Computer, the user can fully realize the capabilities
of the TRS-80 Portable Computer.
The TRS-80 DisklVideo Interface consists of:
•Interface circuit; Transfers data and commands to the TAS-80 Portable Computer.
•Floppy disk drive unit: Drives 5-1/4 inch single-sided, double density floppy disk.
•Floppy disk controller (FDC): Controls driving
of the floppy disk drive unit.
eCentral processing unit (CPU) and memory; Controls interface circuit, floppy disk controller and CRT controller.
To connect
the TRS-80 Disk/Video Interface to the Portable Computer, use the connector cable supplied as an accessory.
Install
the adapter socket provided with the Disk/Video Interface on the System Bus Connector located on the bottom
side of the TRS-80 Portable Computer. Connect one side
of the cable to the adapter socket and the other side to the same
connector located on
the bottom side of the Disk/Video Interface.
1-1

System Overview
Figure 1-1. Disk/Video Interface (Front view)
CD LED Power Indicator: Lights up when the Power Switch is on.
mDrive 0: This is the disk drive unit used for the BASIC SYSTEM diskette.
(}) Drive Select LED: LED lights during access of the diskette.
CD Optional Disk Cover: Remove this cover to install the expansion drive unit. See Appendix A.
oClamp Lever: Turning this lever downward locks the disk drive unit into the operating position.
1-2
•

456
32
7
Figure 1-2. DiskiVideo Interface (Rear view)
CD AC Power Cord: Supplies AC power source to the Disk/Video Interface.
G) PowerSwitch: Turn this switch on to supply AC power to the Disk/Video Interface.
CD Fuse Holder: Contains afuse. Remove the AC cord from the AC receptacle while inspecting/replacing the fuse.
(±) Video Monitor Terminal: Connect your video monitor for a 80 x 25 or 40 x 25 line display.
G) Home TV Terminal: Provides RF output modulated to Channel 3 or Channel 4* of the TV frequency. Connect your
home
TV set to this terminal using the TV cable and switch box supplied.
@) Channel 3/Channel 4Exchange Switch*"': Select either Channel 3or Channel 4RF output (Channell or Channel 2
for Australia), whichever is not used in your area.
(j) System Bus Connector: Connect the system bus connector of the Portable Computer using the attached cable.
~ Channel 1 or Channel 2'for Australia version.
Channel 36 UHF signal for UK/Belgium version.
""_. Deleted for UK/Belgium version.
1-3

Specifications
Operating Voltage:
Power Consumption:
Operating Temperature Range:
Operating Humidity Range:
Dimensions (W x H x O):
Weight:
Disk Drive:
Spindle Rotation Speed
Seek Time
Average Access Time
Motor Starting Time
Data Density
Track Density
Number
of Tracks
Number of Sectors
Bytes/Sector
CRT jnterface;
Display Mode
Display attribution
RF Output Channel
Modulation Ratio
Output Impedance
RF Output Level
Horizontal Scanning Frequency
Vertical Scanning Frequency
120 Volts AC for USA and Canada
220 Volts AC for Belgium
240 Volts AC for UK and Australia
66 Watts
S"C
~ 40°C
20 to 80%
430 x 125 x 300 mm (16-15/16" x 4-15/16" x 11-10/12")
8kg (17.7lbs)
Single,sided, double density
300 R.P.M.
6msec.
88 msec.
500 msec.
5536 B.P.I.
48 T.P.1.
40
18
256 Bytes
40 columns x25 lines or 80 column x 25 lines
Normal,
Blink, Reverse or Reverse and Blink
VHF 3 or 4channel for USA/Canada
VHF 1 or 2channel for Australia
UHF 36 channel for UK/Belgium
75% Typ.
75 ohms
62.5
dBti (67.3 dBf) Typ.
15.625 kHz
60.1 Hz
1-4