Radio Shack TRS-80 User manual

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KEYBOARD, CPU BOARD
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EXPANSION INTERFACE
See Folder CSCS3-A
SAFETY PRECAUTIONS
See page 19
MONITOR
See Folder CSCS3-B
PRELIMINARY SERVICE CHECKS
ENCLOSED
INDEX
Page
Block Diagram 29
Disassembly Instructions 4
General
Operating Instructions 4
GridTrace
Location Guide
CPU Board 13
IC Pinouts &Terminal Guides 6,27
Line Definitions 19
Logic Charts. . . .. ..24,25,26
Miscellaneous Adjustments 20
Parts
List 15,16,17,18
Page
Photos
Cassette Modification Counter Board 20
CPU Board 10,11,12,21,22,23
Level
II ROM Board 14
Partial Keyboard 14
Safety Precautions 19
Schematics
CPU 2,3,30,31,32,33
Power
Supply 5,28
Schematic Notes 9
Troubleshooting 7,8,9
IS,.
Howard W. Sams &Co .. Inc.
4300 West 62nd Street, P.O. Box 7092, Indianapolis, Indiana 46206 U.S.A.
The llliing of ony available replocement port herein dolu not
constitute In any co,. a recommendation. warranty or guoranty by
Howard W. Sam, &Co. Inc .• as to 'hoe qualIty and SUltoblhty of such
replacement port. The numbers of 'hes. parts have been compiled
from information fU"~lIhed to Howard W $oms &Co.. Inc by the
manufacturers of the particular type 01 replacement port listed
Reproduction or use without expre .. permission, of editorial 0( piC1oriol
content in any monner. is prohibited. No poten' Iiobility i, os.Jumed with
respect to the VI. of the information contained herein.
e1985 How"" W. sam, &Co., Inc.
"300 West 62nd Str .. t, P.O. lox 7092. Indianapolis. Indiana <16206 U.S.A.
Pdn'ed in U.S. of Amefico. 85CC14942 DATE 2.85

~ ..... ~ COMPUTCR'C"CTS"' RADIO SHACK TRS·SO
~. '_ lC_III_/""\ __ '_ ' M .... O .. D .. E_L_I_L .. EV_E_L .. I .. I_
PRELIMINARY SERVICE CHECKS
This data provides the user with atime-saving service tool
designed for quick isolation and repair of computer system
malfunctions.
Check all interconnecting cables for good connections and
correct
hookup before making service checks.
MISCELLANEOUS ADJUSTMENTS
Disconnect all external peripherals from the computer
system to eliminate possible external malfunctions.
Replacement or repair of Power Supplies, CPU (Main)
Board, Expansion Interface Board and
Monitor Boards or
connectors may be necessary after the malfunction has
been isolated.
RAM SELECT SHUNT
(Z71) CPU AND KEYBOARD
Type and run the
following Basic program to produce arec-
tangle on the
Monitor screen:
HORIZONTAL AND VERTICAL CENTERING
CPU AND
KEYBOARD
RAM Select Shunt
(Z71) is set up in accordance to the
amount of RAM memory (4K or 16K) installed on
CPU Board.
Use
the following chart to determine which pins are
shunted.
10 CLS: FOR X=0TO 127
20 IF X>47 THEN 40
30 SET (O,X): SET (127,X)
40 SET
(X,O): SET (X,47)
50 NEXT X
60 GOTO 60
ROM SELECT SHUNT (Z3) CPU AND KEYBOARD
NOTE: Perform
12V adjustment before 5V adjustment.
Z3
LEVELl LEVEL II
PINS BASIC BASIC
271
4K 16K
PINS RAM RAM
1-16
Open Shunted
2-15
Shunted Shunted
1-16
Open Shunted
3-14
Open Shunted 2-15 Shunted Open
4-13
Shunted Shunted 3-14 Open Shunted
5-12
Open Shunted 4-13 Shunted Open
6-11
Shunted Shunted 5-12 Open Shunted
7-10
Shunted Shunted 6-11
Shunted Open
8-9
Open Shunted 7-10 Open Open
8-9 Open Open
12V AND
5V ADJUSTMENT CPU AND KEYBOARD
Connect the
input of a DC voltmeter to pin 3of Regulator IC
(Z2). Adjust the 12.0V Adjust Control (Rl0) for 11.9V.
Connect the
input of a DC voltmeter to pin 3of Regulator IC
(Z1). Adjust the 5V Adjust Control (R5) for 5.0V.
12V AND
5V ADJUSTMENT EXPANSION INTERFACE
Rom Select Shunt
(Z3) is set up in accordance to whether
MLevel I or Level II Basic ROMs are installed. Use the follow-
. CJ) ing chart to determine which pins are shunted.
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CJ)
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NOTE: Perform 12V adjustment before 5V adjustment.
Connect the input of a DC voltmeter to pin 3 of Regulator IC
(Z20). Adjust the 12V Adjust Control (R7) for 11.9V.
Adjust the Horizontal Center Control (R20) and Vertical
Center Control
(R21) to center the rectangle on the Monitor
screen.
Connect
the input of a DC voltmeter to pin 3 of Regulator IC
(Z21). Adjust the 5V Adjust Control (R8) for 5.0V.
s
I~ Howard W. Sams &Co., Inc.
lelrTII 4300 West 62nd Street, P.O. Box 7092, Indianapolis, Indiana 46206 U.S.A.
DATE
2-85
85CC14942
R_oductlon 0.- ..... without _p'." pennl .. lon. 01 edltoriol 0.- picto.-lol
conl..,t, In ony manner. i. prohibited. No pot..... liobUlty I. auumed with
r.sp«' to the u .. of the Infarmotlon contolned "-<eln.
~ 11185 Howanl W. Sam. &Co., Inc:.
4300 W .. ,62nd St, .. t. P.O. lax 7092. Indianapolis. Indiana ~ U.S.A.
Printed In U.S. of "memo.
Th. lI,ting of any ovailable r.plocement port tMreln does not
constitute in any cos. 0rec:ommeondotion. warranty or guaranty by
Howard W. Saml &Co .• Inc .. as to the quality and suitability of such
r.ploc.ment port. The numbers of the,. pam hove been compiled
from information furnished to Howard W. $oms &Co.. Inc .. by the
manufacturers of the particular type of replocement port listed.

PRELIMINARY SERVICE CHECKS (Continued)
SERVICE CHECKS
SEE INTERCONNECTING DIAGRAM AND PHOTOS TO MATCH THE NUMBER IN THE
CIRCLES WITH THOSE
IN THE FOLLOWING DATA FOR SERVICE CHECKS TO BE PER-
FORMED.
CD POWER SUPPLY (CPU BOARD)
(A) Disconnect the CPU Power Supply Module (PT1)
from
Connector J1A and check for 18.5VAC be-
tween pin 1and pin 3and 23.6V between pin 2
and pin 4
of the Power Supply Plug (P1A). If the
voltages are missing, replace the Power Supply
Module.
(B) Check for 5.0V at pin 3 of Regulator IC (Z1). If the
measurement is not correct, check the adjust-
ment
of the 5V Adjust Control (R5).
(C) Check for 11.9V at pin 3of Regulator IC (Z2). If
the measurement is not correct, check the ad-
justment of the 12V Adjust Control (R10).
COMPUTER DOES NOT COME
UP PROPERLY
(A) See if the ROM Select Shunts (Z3) and RAM
Select
Shunts (Z71) have been set up properly,
see "ROM Select Shunt Z3"
section of Miscel-
laneous Adjustments.
(B) Check Regulator IC (Z1) and Microprocessor IC
(Z40) by substitution.
(C) Check RAM ICs Z13 thru Z20 by substitution.
KEYBOARD
(A) If only one key is not working properly, clean the
key
contacts with aspray contact cleaner. If the
key is
still defective, check for breaks at the key
contacts and solder joints. Check the key con-
tacts with an ohm meter.
(B) If several keys are not working, check the ribbon
cable between Keyboard and
CPU board for
possible open circuits.
(C) If wrong character appears on the Monitor
screen when akey is pressed. Check Character
Generator IC
(Z29) by substitution.
@NO VIDEO ON MONITOR
(A) Check the video cable for broken wires and the
Video
Connector (J2) for good connection.
(B) Check the adjustment of the Contrast Control
(R102) and Brightness Control (R103) located on
the Monitor.
VIDEO DISPLAY NOT CENTERED
ON MONITOR
(A) Check the adjustment of the Horizontal Center
Control
(R20) and Vertical Center Control (R21)
on the CPU Board, see" Horizontal and Vertical
Centering" section of Miscellaneous Ad-
justments.
II
CD VIDEO DISPLAY UNSTABLE
(A) Check the adjustment of the Horizontal Hold
Coil (L4) and Vertical Hold Control (R13B)
located on the rear of the Monitor.
®MONITOR DEAD
(A) Check Fuses F101 and F103 located inside the
Monitor.
®CASSETTE PORT INOPERATIVE
(A) Check the Cassette cables for loose or broken
wires and also check
Connector J3 on CPU
Board and Connectors J6, J7 and J8 on Expan-
sion Interface Board
for good connections.
(B) If the Cassette motor will not stop running, turn
the Computer Off. Use
an ohm meter to check
for an open circuit from the center pin at one end
of Relay K1 to the center pin at the other end of
Relay K1. If the pins are shorted, either Relay K1
contacts are sticking or Diodes CR9 and CR10
are shorted.
POWER SUPPLY (EXPANSION INTERFACE)
(A) Disconnect the Expansion Interface Power Sup-
Iy Module (PT1) from
Connector J9 and check for
19.7VAC between pin 1and pin 3and 23.6V DC
between pin 2and pin 4 of the Power Supply
Plug
(P9). If the voltages are missing, replace the
Power Supply Module.
(B) Check for 11.9V at pin 3 of Regulator IC (Z20). If
the measurement is incorrect, check the adjust-
ment
of the 12V Adjust Control (R7).
(C) Check for 5.0V at pin 3 of Regulator IC (Z21). If
the measurement is incorrect, check the adjust-
ment of the 5V Adjust Control (R8).
DISK DRIVE PORT INOPERATIVE (EXPANSION
INTERFACE)
(A) Check Disk Drive cables for loose or broken
wires and
Connector J5 for good connections.
Clean Connector J5 contacts with a contact
cleaner.
(B) Check Disk Controller IC (Z42) by substitution.
LINE PRINTER PORT INOPERATIVE (EXPANSION
INTERFACE)
(A) Check the Line Printer cable for loose or broken
wires and Connector J4
for good connections.
Clean
Connector J4 contacts with a contact
cleaner.

J3
SU'"FERED
INTERFACE
IllS
PORT
40
52
RESET
39
HI~
@) Z40
2 40 '--------I
"Y"
®
FWl lCa
40
CASSETTE CASSETTE
2I
L
.J
Y
@)
J1
34 JS 2
DISK MIVE
PORT
Q34
DISK ~
CCWTROlLER 8L t:.:
PRINTER
PORT
Q2
142 \!.J
8RIO
@ CJ@
Rf6lLAT~ Rf6tl.AT~
5.~ m
@) EJ /6
11.9V
BBBBBBBB
EXPANSION INTERFACE BOARD
PRELIMINARY SERVICE CHECKS (Continued)
CPU BOARD
19.7VAC
MON ITOR V IDEO
BOARD
CASSETTE
HOOIF lCATlOH
COUOfTER
!IOARD
{
HOR~
@ CENTER
R21
VERT
r-----~ CENTER
0-----
VERT Q
SIZE
rnD _
LEVEL IT ROM BOARD
MONITOR MAIN BOARD
P I
CPU
POWER SlI'flt y
@
HORI1 @ VERT
I«llD HCl.D
PRELIMINARY SERVICE CHECKS (Continued)
@
F103 0
]A
®
F~' 0
I20VAC
8 ~-~
.... 'V'----.,
MONITOR CHASSIS
Z33
FWl
SHMTS
KEYBOARD
INTERCONNECTING DIAGRAM
X
INTERCONNECTING DIAGRAM
III

PRELIMINARY SERVICE CHECKS (Continued)
GENERAL OPERATING INSTRUCTIONS
POWER UP (COMPUTER ONLY)
Turn On the Computer. The
words nMEM SIZE?" will ap·
pear on the
Monitor screen. Press the Enter key once. The
word" READY" and a prompt character will appear on the
Monitor screen. The Computer is now in Basic mode.
POWER
UP SEQUENCE (WHEN USING DISK DRIVE)
1. Turn On the Expansion·Interface.
2. Turn On the Disk Drives (Terminal Drive 26·1164A, first)
and then any
other peripherals.
3. Put a diskette (containing DOS, Disk Operating System)
into Disk Drive O. Turn On the Computer. The Computer
will automatically boot up from Disk Drive O. The version
of
the Disk Operating System will appear on the Monitor
screen along with the words "DOS READY" and a
prompt character.
NOTE:
If an Expansion Interface unit is used without a
Disk Drive,
hold down Break key when turning On Com·
puter. A
double" MEM SIZE?" will appear on Monitor
screen. Press Enter key and the word" READY" will ap·
pear followed by a
prompt character. The Computer is
now in Basic mode.
RESET
Press the Break key and the Reset
button (on right rear of
the Computer) to reset the Computer to Basic mode. If Disk
Drives are attached, insert a diskette containing DOS infor-
mation into Disk Drive 0and press only the Reset button.
This will reboot the Computer from Disk Drive O.
DISK OPERATING SYSTEM (DOS)
Type DIR and press the Enter key
to display a directory of
programs
that are on the diskette in Disk Drive O. Type DIR :
and the
number of the Disk Drive holding the diskette which
contains the information desired. Example: Type DIR :2 to
list programs on diskette in Disk Drive 2.
To load aprogram from a diskette, type the name of the pro-
gram and press the Enter key. Use a
colon and the number
of the Disk Drive which contains the program to be loaded_
If no
number is given, the system will assume Disk Drive O.
NOTE: Basic program will not load from diskette unless the
Computer is in the Disk Basic mode.
To get back to the DOS from Disk Basic mode, type
IV
CMD"S" and press the Enter key. Any program in memory
will be lost when leaving Basic mode by using "CMD"S".
DISK BASIC
To load Disk Basic
into the Computer, boot up on DOS. In-
sert a
diskette containing Disk Basic (usually apart of the
DOS
diskette) into Disk Drive 0, type BASIC, press the Enter
key and
follow prompts. To go from Disk Basic mode to
DOS, type CMD"S" and press the Enter key. Any program
in memory
will be lost.
To load aprogram from a
diskette, type LOAD and the pro-
gram name enclosed in
quotes and press the Enter key. To
load from aDisk Drive
other than Drive 0, add a colon and
the
Disk Drive number at the end of the program name. Ex-
ample: LOAD
"SAMS:1" for Disk Drive 1.
To save aprogram onto a diskette in aDisk Drive, type
SAVE and the program name in
quotes and press the Enter
key. To save aprogram onto a diskette in aDisk Drive other
than Disk Drive 0, add a colon and the Disk Drive number at
the end
of the program name. Example: SAVE "SAMS:1" for
Disk Drive 1.
FORMATIING A DISKETIE
NOTE: This procedure does not copy Disk Operating
System
sections required for normal disk operations. A
diskette thus formatted must be used only with systems
containing 2 or more Disk Drives. Use" Back-up" function
to format a diskette containing DOS information.
Ablank diskette must be formatted before it can be used for
saving data. To format a diskette, boot up on DOS, insert a
diskette with the format program on it (usually part of the
DOS
diskette) into the Disk Drive, type FORMAT and press
the Enter key.
After the program has been loaded, insert a
blank
diskette into the Disk Drive and follow the instruc-
tions on the Monitor screen.
CASSETIE OPERATION
To load aprogram from tape, type CLOAD (with
or without
the program name enclosed in quotes), put the Recorder in
play
mode and press the Enter key. Prompt will indicate
when program has been loaded.
To save aprogram
onto tape, save CSAVE (with or without
the program name enclosed in quotes), put the Recorder in
record mode and press the Enter key. A
prompt will in-
dicate when writing has been completed.

PRELIMINARY SERVICE CHECKS (Continued) PRELIMINARY SERVICE CHECKS (Continued)
CE TER
HORll
R20
{
CR9
@ K1
CR10
CPU BOARD
VIII
®
CASSErE
J3
@
Af1A\
f3C\ ~ POWER
V DEO ~ POWtR SW TCH
J2 Z29 J1 Sl
r®
..
@@®@
ROM
SELECT SHU TS
Z3
@
RAM
SELECT SHU TS
Z71
Z40 @
KEYBOARD ®
CABLE
CPU BOARD
V

PRELIMINARY SERVICE CHECKS (Continued)
12V ADJ
{
R7--
@120V
PI 3
Z20
5V AoJ
@{ R8
~ OV
PI 3
Z21-....JIi==
POWER
J9
@
..
PRELIMINARY SERVICE CHECKS (Continued)
G~0
OS DR E paR
J5
LINE
PRI TER
~~_j~RT @
BUFFERED
INTERFACE
BUS
PORT
~~-J3
:tl
3:>
0
52
00
m(f)
r-z
->
r-(')
m~
<0004
~:tl
_(f)
-eo
o
EXPANSION INTERFACE BOARD
VI
EXPANSION INTERFACE BOARD
VII

PRELIMINARY SERVICE CHECKS (Continued) PRELIMINARY SERVICE CHECKS (Continued)
CE TER
HORll
R20
{
CR9
@ K1
CR10
CPU BOARD
VIII
®
CASSErE
J3
@
Af1A\
f3C\ ~ POWER
V DEO ~ POWtR SW TCH
J2 Z29 J1 Sl
r®
..
@@®@
ROM
SELECT SHU TS
Z3
@
RAM
SELECT SHU TS
Z71
Z40 @
KEYBOARD ®
CABLE
CPU BOARD
V

PRELIMINARY SERVICE CHECKS (Continued)
PREVENTATIVE MAINTENANCE
ENVIRONMENT
Computers perform best in aclean, cool area that is below 80 degrees Fahrenheit and free of dust and smoke particles. Even
though home Computers are not affected by cigarette smoke as much as commercial Computers are affected, it is belter to
maintain asmoke-free area around the Computer. Do not block cabinet vents of any of the Computer system; Computer,
Monitor, Printer, or other power devices.
ELECTRICAL POWER
Variations in the line voltage can affect the Computer. Try to avoid these fluctuations by using an AC receptacle that is on a
power line not used by appliances or other heavy current demand devices. Apower-surge protector, power-line conditioner, or
non-interruptable power supply may be needed to cure the problem. Do not switch power On and Off frequently.
KEYBOARD
liquids spilled into the Keyboard can ruin it. Immediately after a spill occurs, disconnect the Computer power plug from AC
power outlet. Then, if circuitry or contacts are contaminated, disassemble the Keyboard and carefully rinse the Keyboard
printed
circuit board with distilled water and let it dry. Use a colton swab to clean between the keys. Use anon-abrasive con-
tact cleaner and lint-free wipers on accessible connectors and contacts.
DISK DRIVES
Clean the read/write heads of the Disk Drives about once a month or after 100 hours usage. Use only an approved head clean-
ing kit.
Handle
carefully to preserve proper disk head alignment. Asudden bump or jolt to the Disk Drives can knock the disk head out
of alignment. If the disk drive must be transported, place an old disk in slot and close door during transport.
Store
disks in their protective covers and never touch the disk surface. Observe the disk handling precautions usually found
on the back of
disk protective covers.
PRINTERS
Carefully vacuum the Printer regUlarly. Wipe surface areas clean using a light all-purpose cleaner. Do not oil the machine.
The oil
will collect abrasive grit and dust. The dust will act as ablanket. This can cause components to overheat and fail.
STATIC ELECTRICITY
Static electricity discharge can affect the Computer. In order to minimize the possibility, use anti-static mats, sprays, tools
and materials, and maintain good humidity in the Computer environment.
MONITOR
Use an isolation transformer with any Monitor that does not come as part of the system since some Monitors use aHOT
chassis (chassis connected to one side of the AC line). The face of the Monitor should never be left on for long periods of time
at high brightness level except when pattern is being changed periodically. Use caution when cleaning anti-glare screens, to
preserve the glare-reduction feature.
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->
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IX

J3
SU'"FERED
INTERFACE
IllS
PORT
40
52
RESET
39
HI~
@) Z40
2 40 '--------I
"Y"
®
FWl lCa
40
CASSETTE CASSETTE
2I
L
.J
Y
@)
J1
34 JS 2
DISK MIVE
PORT
Q34
DISK ~
CCWTROlLER 8L t:.:
PRINTER
PORT
Q2
142 \!.J
8RIO
@ CJ@
Rf6lLAT~ Rf6tl.AT~
5.~ m
@) EJ /6
11.9V
BBBBBBBB
EXPANSION INTERFACE BOARD
PRELIMINARY SERVICE CHECKS (Continued)
CPU BOARD
19.7VAC
MON ITOR V IDEO
BOARD
CASSETTE
HOOIF lCATlOH
COUOfTER
!IOARD
{
HOR~
@ CENTER
R21
VERT
r-----~ CENTER
0-----
VERT Q
SIZE
rnD _
LEVEL IT ROM BOARD
MONITOR MAIN BOARD
P I
CPU
POWER SlI'flt y
@
HORI1 @ VERT
I«llD HCl.D
PRELIMINARY SERVICE CHECKS (Continued)
@
F103 0
]A
®
F~' 0
I20VAC
8 ~-~
.... 'V'----.,
MONITOR CHASSIS
Z33
FWl
SHMTS
KEYBOARD
INTERCONNECTING DIAGRAM
X
INTERCONNECTING DIAGRAM
III

PRELIMINARY SERVICE CHECKS (Continued)
TEST EQUIPMENT AND TOOLS
TEST EQUIPMENT
Digital Voll/Ohm Meter
logic Probe
TOOLS
Phillips Screwdriver
Small Screwdriver
Contact Cleaner
low Voltage Soldering Iron
Desoldering Equipment
PARTS LIST AND DESCRIPTION
CPU BOARD EXPANSION INTERFACE BOARD
ITEM PART NO. DESCRIPTION ITEM PART NO. DESCRIPTION
CR9 4800026 Diode, 1N982A
PT1
4000004 Power Supply Module
CR10 4800026 Diode, 1N982A
R7
4750019 Control,
12V Adjust,
K1
4500001
Relay, Motor Control, 5V
1000 Ohms
PT1
40ססoo4
Power Supply Module
R8
4750019 Control,
5V Adjust,
R5
4750019 Control,
5V Adjust, 1000 Ohms 1000 Ohms
R10
4750019 Control, 12V Adjust, Z20
31ססoo1
IC, Regulator, MC1723CP
1000 Ohms
Z21
31ססoo1
IC, Regulator, MC1723CP
:XI
R20 4750018 Control, Horizontal Center, Z42 IC, Disk Controller,
s::J>
100K Ohms
FD1771 B-{)1
02
00
R21
4750018 Control, Vertical Center,
men
100K Ohms
"I
Z1
3100001
IC, Regulator, MC1723CP MONITOR
-:J>
10
Z2
31ססoo1
IC, Regulator, MC1723CP
m"
Z3
2100041
Shunt, ROM Select ITEM PART NO. DESCRIPTION
<-i
Z13 3108009 IC, RAM, MB8116E
~:XI
_Cf)
thru 3108003(1) IC, RAM,
F101
426973 Fuse, 1A @250V, Fast
Acting
-ciD
Z20 F103 99328 Fuse, 5A @250V, Fast
Acting
0
Z29 IC, Character Generator,
L4
141017 Coil Horizontal Hold
8046670 R13B 141022 Control, Vertical Hold,
3108001 IC, Character Generator, 200K Ohms
MCM6670
R102
140980 Control, Contrast, 500 Ohms
Z40 IC, Microprocessor,
D780C·1
R103
140711
Control, Brightness,
3110001
IC, Microprocessor, Z80 200K Ohms
Z71
2100041
Shunt, RAM Select
(1) Used in 4K versions
DISASSEMBLYINSTRUCTIONS
CABINET REMOVAL CPU AND KEYBOARD
Remove six screws from cabinet bottom. Remove cabinet
top and bottom from Keyboard and CPU Board. All com-
ponents are now accessible for service.
CABINET REMOVAL EXPANSION INTERFACE
Remove six screws from cabinet bottom. Remove cabinet
bottom from unit. All components are now accessible for
service.
CABINET REMOVAL MONITOR
Remove five screws holding cabinet back and remove back.
All components are now accessible for service.
XI

SH74LSOON
PART a: 174
H04
HaS
H06
H07
HOO
HOI
H02
H03
SH74LS004N
PART a: 152
D7
2./1'1
2p
MB811SE
aZ13
RAH
os
2p
H6811SE
eZ14
RAH
OS
:2 p
1t8811SE
a Z20
RAH
04
2.6V
2p
MBBIISE
aZ15
RAH
HOTE. 173 B,9,10
r.;---4~----..;t-----<>-<>-__tl?1+---_;------.c~I...}~ b--!':----" AKJ 174 PINS 1" 12, 13
U5£D I NEARlY
VERSIONS
SH74L532N
PART a: 173
D3
2p
2./1'1
1t8811SE
a119
RAH
02
2.5Y
2p
MBBllSE
e118
IWfE
2./1'1
01
2p
MBBIISE
a116
RAH
CABLING.
HEAVY LINES REDUCE
USE OF MULTIPLE LINE
Z3
AI2--------......:.-I
AI3---------.:.-I
AH--------+-T.;..t
LINE IDENTIFICATION
ASSIGNED FOR REFERENCE
RADIO SHACK TRS·80
MODEL ILEVEL II
A15
PHOTO CIRCUlTRACE: =m
sa£H), TIC CI RCUlTRACE: = [D]
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PART a: 174
APHOTOfACT STANDARD NOTATION SCHEMATIC
WITH Ii'·i.i1n.,., ••
©Howard W. Sam. &Co .• Inc. 1985
R69
4700
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FOR TERMINAL GUIDES AND NOTES
SEE PAGES 6,9,27
CABLING.
HEAVY LINES REDUCE
USE OF MULTIPLE LINE
LINE
IDENTIFICATION ASSIGNED FOR REFERENCE
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TO
EXPANSION
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SYNC
A PHOTOPACT STANDARD NOTATION SCHEMATIC
WITH li'·iYili'-f.'i.
@Howard W. Sama &Co .• Inc. 1985
SEE LINE DEFINITIONS ON PAGE 19
30
J

GENERAL OPERATING INSTRUCTIONS
POWER UP (COMPUTER ONLY)
Turn On the Computer. The words
"MEM SIZE?" will ap·
pear on the
Monitor screen. Press the Enter key once. The
word "READY" and a
prompt character will appear on the
Monitor screen. The Computer is now in Basic mode.
POWER
UP SEQUENCE (WHEN USING DISK DRIVE)
1. Turn On the Expansion Interface.
2. Turn On the Disk Drives (Terminal Drive 26·1164A, first)
and then any
other peripherals.
3. Put a diskette (containing DOS, Disk Operating System)
into Disk Drive O. Turn On the Computer. The Computer
will automatically boot up from Disk Drive O. The version
of the Disk Operating System will appear on the Monitor
screen along with the words "DOS READY" and a
prompt character.
NOTE: If an Expansion Interface
unit is used without a
Disk Drive, hold
down Break key when turning On Com·
puter. A
double "MEM SIZE?" will appear on Monitor
screen. Press Enter key and the word" READY" will ap-
pear
followed by a prompt character. The Computer is
now in Basic mode.
RESET
Press
the Break key and the Reset button (on right rear of
the Computer) to reset the Computer to Basic mode. If Disk
Drives are attached, insert a
diskette containing DOS infor-
mation
into Disk Drive 0and press only the Reset button.
This
will reboot the Computer from Disk Drive O.
DISK OPERATING SYSTEM (DOS)
Type DIR and press the Enter key
to display a directory of
programs that are on the diskette in Disk Drive O. Type DIR :
and the
number of the Disk Drive holding the diskette which
contains the information desired. Example: Type DIR :2 to
list programs on diskette in Disk Drive 2.
To load aprogram from adiskette, type the name of the pro-
gram and press the Enter key. Use a
colon and the number
of the Disk Drive
which contains the program to be loaded.
If
no number is given, the system will assume Disk Drive O.
NOTE: Basic program will not load from diskette unless the
Computer is in the Disk Basic mode.
To get back to the DOS from Disk Basic mode, type
CMD"S" and press the Enter key. Any program in memory
will be lost when leaving Basic mode by using "CMD"S".
DISK BASIC
To load Disk Basic
into the Computer, boot up on DOS. In·
sert a
diskette containing Disk Basic (usually apart of the
DOS diskette)
into Disk Drive 0, type BASIC, press the Enter
key and
follow prompts. To go from Disk Basic mode to
DOS, type CMD"S" and press the Enter key. Any program
in memory
will be lost.
To load aprogram from adiskette, type LOAD and the pro-
gram name enclosed in
quotes and press the Enter key. To
load from aDisk Drive
other than Drive 0, add a colon and
the Disk Drive number at the end
of the program name. Ex-
ample: LOAD "SAMS:1" for Disk Drive 1.
To save aprogram onto a diskette in aDisk Drive, type
SAVE and the program name in
quotes and press the Enter
key. To save aprogram onto a diskette in aDisk Drive other
than Disk Drive 0, add acolon and the Disk Drive number at
the end
of the program name. Example: SAVE "SAMS:1" for
Disk Drive 1_
FORMATIING ADISKETIE
NOTE: This procedure does not copy Disk Operating
System
sections required for normal disk operations. A
diskette thus formatted must be used only with systems
containing 2or more Disk Drives. Use" Back-up" function
to format a diskette containing DOS information.
Ablank diskette must be formatted before it can be used for
saving data. To format adiskette, boot up on DOS, insert a
diskette with the format program on it (usually part of the
DOS diskette)
into the Disk Drive, type FORMAT and press
the Enter key.
After the program has been loaded, insert a
blank
diskette into the Disk Drive and follow the instruc·
tions on the Monitor screen.
CASSETIE OPERATION
To load aprogram from tape, type CLOAD (with or
without
the program name enclosed in quotes), put the Recorder in
play mode and press the Enter key. Prompt
will indicate
when program has been loaded.
To save aprogram
onto tape, save CSAVE (with or without
the program name enclosed in quotes), put the Recorder in
record mode and press the Enter key. A
prompt will in-
dicate when writing has been completed.
DISASSEMBLY INSTRUCTIONS
CABINET REMOVAL
Remove
six screws from cabinet bottom. Remove cabinet
top and bottom from Keyboard and CPU Board. All com·
ponents are now accessible
for service.
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FOR TERMINAL GUIDES AND NOTES
SEE PAGES 6,9,27
PHOTO CIRCUITRACE =m
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APHOTOPACT STANOARD NOTATION SCHEMATIC
WITH ""·i'ini·f.iM'
©Howard W. Sama &Co., Inc. 1985
POWER SUPPLY
28
5

TERMINAL GUIDES & Ie PINOUTS
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8 GNO
A9 39
A8 38
A7 37
A636
AS 3~
A4 34
AD 30
AI 31
A3 33
A2 32
,AIO 40
WAIT 24
GNO 29
mil 28
iI 27
RESET 26
~2~
!lrolii 23
WR 22
Rli 21
071OC·1
240
MICROPROCESSOR
TOP VIEW
4 AU
3 Al3
All
A12
~ AI~
6 ClK
7 04
8 03
9 3~
10 06
19 liIl£ll
20 fORO
12 02
13 07
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1400
DATA
INPUTS
13
9 OUTPUT
12
11
10
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27.269.270
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t--+..:;A:.,:
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OUTPUT 7
DATA
INPUTS
I
INPUT 8 INPUT A1
1 1
BX
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SHIfT REGISTER
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238
DECODER
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SH74LS42H
ClOCK
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ClOCK 7
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SELECT I
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OUTPUT 4
INPUTS{:
OUTPUT 7
8 GNO
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DECODER
TOP VIEW
u
12
11
13
10
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40 13
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511741.$17511
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100 l'
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ZS, 26, Z57
TOP VIEW
l[]"
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lIA, l2A,
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230. 236. 237,
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TOP VIEW
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TOP VIEW
vz
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7 V-
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2
CURRENT
LIMIT
3 CURRENT
SENSE
4 INVERTING
INPUT
~ NON INVERTlHG
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6 ¥REf
21L028
RESET PI4 12
6 CLK PI3 II
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8GNO PIl9
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TOP VIEW
J QI VOO 16
2 T.t Q2 I~
3 K Q3 14
Q4 13
8046670
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CHARACTER GENERATOR
TOP VIEW
1188116E
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fRONT VIEW
I YOO vee 9
ZI3 THRU Z20
RAIl
TOP VIEW
7 AI A~ 10
1 V88 VSS 16
2 DIN CAS 15
3 WI: OOUT 14
4 RAS A6 13
~ AD A3 12
6 A2 A4 II
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15
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RESET 11
jfi 10
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80nOll VIEW
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I Q12
2 Q6
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4 Q7
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6 Q3
7 Q2
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fRONT VIEW
Q4
80nOll VIEW
241
DRIVER
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TOP VIEW
JlA, II. J3
fRONT VIEW
SlI74U92H
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DIVIDE 8Y 6.
DIVIDE 8Y 12
TOP VIEW
l22, 13l, l39, 244,
m, 260, Z67, 26&,
m. Z75, Z76
TRI,STATE 8UffER
TOP VIEW
1 I
2
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IHPUT IHPUT
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4
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61----
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627

POWER SUPPLY
TROUBLESHOOTING
CPU CLOCK AND DIVIDER
Computer is dead. Disconnect the Power Supply (PT1) from
the CPU Board. Check for 18.5VAC between pin 1and pin 3
of Connector J1A and 23.6V between pin 4and pin 2 of Con-
nector J1A. If the voltages are missing, check the cable and
connections at Connector J1A and check for open AC
power cord. If the correct voltages are present, reconnect
the Power Supply to the CPU Board and turn On the Com-
puter. Check for 5.0V at pin 3 of Regulator IC (Z1), 11.9V at
pin 3 of Regulator IC (Z2) and -5.0V at the anode of Zener
Diode CR2. If all the voltages are missing, check the Power
Switch (S1).
If 5.0V is missing, check the voltages and components
associated with Regulator Output Transistor (04),
Regulator Drive Transistor (03), Error Amp Transistor (05)
and pins 2thru 7, 10, 11 and 13 of IC Z1. If the 5.0V is incor-
rect, check the adjustment of the 5V Adjust Control (R5),
refer to "Miscellaneous Adjustments".
If the 11.9V is missing, check the voltages and components
associated with Regulator Output Transistor (06) and pins 2
thru 7, 10, 11 and 13 of IC Z2. If the 11.9V is incorrect, check
the adjustment of the 12V Adjust Control (R10).
If the -5.0V is missing, check Resistor (R19), Zener Diode
CR2 and check for possible short to ground.
MICROPROCESSOR (CPU) OPERATION
Check the 1.774MHz clock waveform at pin 6of Micro-
processor IC (Z40). If the waveform is missing or off fre-
quency, refer to the "CPU Clock and Divider" section of this
Troubleshooting guide.
If the waveform is normal, check the operation of the reset
signal at pin 26 of IC Z40. The logic reading at pin 26 should
be Low for approximately .1 second when the Computer is
turned On and then change to and remain High. If the logic
reading is incorrect, check Capacitor C42, Resistor R47 and
check ICs Z52 and Z53 by substitution.
If the logic reading at pin 25 of IC Z40 is Low, the data lines
(pins 7thru 10 and 12 thru 15 of IC Z40) and address lines
(pins 1thru 5and 30 thru 40 of IC Z40) will be disabled.
When disabled the logic readings for the data lines are High
and the address lines are Open (No lights On). The logic
readings at the inputs and outputs of the address line buf-
fers, Tri-State Buffer ICs (Z22, Z38, Z39 and Z55), will also
read Open (No lights On). If the logic reading at pin 25 of IC
Z40 is Low, check Resistor R58 and check for apossible
short to ground. The dataand address lines from IC Z40 can
be checked by grounding pin 25 of IC Z40 and checking the
logic readings for High on the data lines and for Open (No
lights On) on the address lines.
If IC Z40 appears to start operating when the computer is
turned On and suddenly stops, pulses appear on data lines
then suddenly stop, check ROM AlB IC (Z1 B) RAM ICs (Z13
thru Z20) by substitution.
Verify that the CPU Clock is operating properly by checking
for afrequency of 10.6445MHz at pin 6 of IC Z42. If the
clock is off frequency, check 10.6445MHz Crystal (Y1) and
Capacitor C43. If the clock is not operating, check Crystal
Y1, Capacitor C43, Resistors R46 and R52 and check IC Z42
by substitution.
The 10.6445MHz clock is divided by six by the Divide By 61C
(Z56) to supply the 1.774MHz clock, pin 8of IC Z56, and fed
to pin 6 of Microprocessor IC (Z40). Check for afrequency
of 1.774MHz at pin 8 of IC Z56. If the frequency is incorrect
or the signal is missing, check the logic reading at pin 6 of
IC Z56 for aLow. If the logic reading at pin 6is High, check
Resistor R67 and check IC Z42 by substitution. If the logic
reading at pin 6is Low, check IC Z56 by substitution. Check
for pulses at pin 6 of IC Z40. If pulses are missing, check
Resistor R64 and check Tri-State Buffer IC (Z72) by substitu-
tion.
VIDEO
No video on the Monitor screen. Check the waveform at the
emitter of the Video Output Transistor (01). If the waveform
is normal, check the Video Connector (J2) for good connec-
tion and check the video cable.
If the waveform is missing at the emitter of Transistor 01,
check for avideo signal at pin 5 of Driver IC (Z41). If the
signal is present at pin 5of IC Z41, check the voltages and
components associated with Transistor 01. If signal is
missing at pin 5 of IC Z41, check for avideo signal at pin 6 of
IC Z41. If the signal is present, check IC Z41 by substitu-
tion. If the signal is missing from pin 6 of IC Z41, check the
waveform at pin 3of IC Z30.
If the waveform is present at pin 3 of IC Z30 and the logic
reading at pin 2 of IC Z30 is Low, check IC Z30 by substitu·
tion. If the logic reading at pin 2of IC Z30 is High, check the
Shift Reg (Register) IC (Z11) by substitution. If the wave-
form is missing at pin 3 of IC Z30, check the waveform at pin
15 of Shift Reg (Register) IC (Z10) and check for pulses at
pins 4, 5,10,11 and 12 of IC Z10. If the waveform and pulses
are present, check IC Z10 by substitution.
Video display does not operate in the 32 character mode.
Type and run the following Basic program and check for
pulses at pins 9and 14 of Flip/Flop IC (Z59).
10 OUT 255,8: OUT 255,0: GOTO 10
If pulses are missing at pin 9 of IC Z59, check for pulses at
pins 9and 10 of IC Z25. If pulses are missing from pin 9 of
IC Z25, check Tri-State Buffer IC (Z22) and ICs Z23 and Z52
by substitution. If pulses are missing from pin 10 of IC Z25,
check ICs Z36, Z52 and Z54 by substitution. If pulses are
present at pin 9and 10 of IC Z25, check IC Z25 by substitu-
tion.
If pulses are present at pin 9 of IC Z59 and missing at pin 14
of IC Z59, check IC Z59 by substitution. If pulses are pre-
sent at pin 14 of IC Z59, check Mux (Multiplexer) IC (Z43) by
substitution.
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VIDEO RAM
TROUBLESHOOTING (Continued)
KEYBOARD
The
following Basic program can be used to check the RAM
ICs (Z45 thru Z48 and
Z61 thru Z63). The program checks
each
bit of RAM and displays on the Monitor screen any
defective
bit found. If aPrinter is connected to the Com-
puter,
the bad bit message can be sent to the Printer by
changing the word PRINT in lines 130 and 150
to the word
LPRINT.
VIDEO RAM TEST PROGRAM
5DATA
1, 2, 4,8,16,32,128
10 Y = 6: X= 15360: POKE X,64
20 IF (PEEK (X) AN 0 64) = 64 TH EN 30 ELSE 150
30 POKE X,160
40 IF (PEEK (X) AND 64) = 0 THEN 50 ELSE 150
50 FOR X= 15360 TO 16383
60 FOR Y=O TO 6
70 READ Z: POKE X,Z
80 IF (PEEK (X) AND Z) = Z THEN 90 ELSE 140
90 POKE X,O
100 IF (PEEK (X) AND Z)=O THEN 110 ELSE 140
110 NEXT Y
120 RESTORE: NEXT X
130 PRINT "MEMORY GOOD" :END
140 IF Y = 6 TH EN Y = 7
150 PRINT "BIT"; Y; "OF MEMORY LOCATION"; X;
"CHECKS BAD"
160 IF Y = 6 THEN 50 ELSE 110
Keyboard is
not functioning. Check the ribbon cable be·
tween Keyboard and
CPU Board for open circuits. If the rib-
bon cable checks good, check
for pulses at pin 11 of IC Z36.
If pulses are
missing, check IC Z36 by substitution.
If a group of keys are not functioning, check the pins of ICs
Z1A and Z2A and Tri-State Inverter ICs (Z3A and Z4A) con-
nected
to the keys not functioning. Also check the ribbon
cable
for open circuits.
If asingle key does not function, check the key contacts
with an ohmmeter. If the key is erratic and intermittent in
operation, clean the
contacts with aspray contact cleaner.
If awrong character shows up on the
Monitor screen when
an alpha or numeric key is pressed, check the video RAM,
refer
to the "Video RAM" section of this Troubleshooting
guide and check Flip/Flop IC (Z28) and Character Generator
IC
(Z29) by substitution.
CASSETIE
Computer will not save programs onto tape or will not turn
On the cassette motor. Type and run the
following Basic
program. The program will produce the waveform shown in
Figure 1at pin 2
of Flip/Flop IC Z59 and will toggle On and
Off Motor Control Relay (K1) on the CPU Board and Relay
(K1) on the Expansion Interface Board.
The
bit number that each RAM IC produces is noted on the
schematic. IF the program finds abad bit, check the
schematic for the RAM IC that produces that bit and check
that RAM IC by
substitution.
NOTE: No RAM IC is used for bit 6. Bit 6is produced by
comparing
bits 5and 7 with aNOR Gate IC Z30. If the pro-
gram
indicates bit 6is bad and bits 5and 7are good, check
IC Z30 by substitution.
Tri-State Buffer ICs (Z44 and Z60) are used to connect the
RAM IC
outputs to the data lines. If abad bit is found and
the RAM IC checks good, check the Tri-State
Buffer associ-
ated
with the defective bit by substitution.
Figure 1
3.5V
5ms
OV
DC
Reference
VIDEO SYNC
No vertical sync. Check the waveform at pin
11 of Counter
IC
(Z32). If the waveform is missing, check IC Z32 by
substitution. If the waveform is present, check the
waveform at pin 8of IC Z57. If the waveform is
missing at
pin
8, check the Vertical Center Control (R21), Capacitors
C26 and C27 and check IC Z57 by substitution. If the wave-
form is present at pin
8, check IC Z5 by substitution.
No horizontal sync. Check the waveform at pin 11 of
Counter IC (Z50). If the waveform is missing, check IC Z50
by
substitution. If the waveform is present, check the wave·
form at pin 8
of IC Z6. If the waveform is missing at pin 8,
check the Horizontal Center Control (R20), Capacitors C20
and
C21 and check IC Z6 by substitution. If the waveform is
present at pin 8of IC
Z6, check IC Z5 by substitution.
No vertical or horizontal sync. Check the waveforms at pin
8
of IC Z5. If the waveforms are missing, check IC Z5 by
substitution. If the waveforms are present, check Resistors
R28 and R29 and Sync Amp Transistor (02).
8
10 FOR X= 1 TO 100
20 OUT 255,3: OUT 255,0
30 NEXT X
40 OUT 255,4: POKE 14308,0
50 FOR X= 1 TO 100
60 OUT 255,7: OUT 255,4
70 NEXT X
80 POKE 14308,1: GOTO 10
If the Cassette Motor is not switching On, listen for a click·
ing sound from Relay K1 on the CPU Board. If the Relay is
clicking, check Relay K1 contacts with an ohmmeter and
check the connections at pins 1and 3 of Connector J3. If
Relay
K1 is not clicking, check the logic reading at pin 1of
Driver IC
(Z41). The logic reading should be toggling bet-
ween Low and High. If the
logic reading is correct, check
for a logic reading that toggles between Low and High at
pin 3of IC Z41. If the
logic reading is incorrect at pin 3 of IC
Z41, check IC
Z41 by substitution. If the logic reading is
correct at pin 3, check Relay K1 and Diode CR3. If the
reading at pin 1
of IC Z41 is incorrect, check for pulses at
pin 9
of Flip/Flop IC (Z59). If pulses are present at pin 9,

TROUBLESHOOTING (Continued)
SCHEMATIC NOTES
~ Circuitry not used in some versions
Circuitry used in some versions
8See parts list
.... Ground
Item numbers in rectangles appear in the alignment/adjust-
ment instructions.
Supply voltage maintained as shown at input.
Voltages measured with digital meter.
Voltages and Waveforms taken with computer in Power Up
mode (Main title screen displayed) unless otherwise
noted. Waveforms taken with triggered scope and
SweeplTime switch in Calibrate position, scope input
set for DC coupling on "0" reference voltage waveforms.
Switch to AC input to view waveforms after DC reference
is measured when necessary. Each waveform is 9cm
width with DC reference voltage given at the bottom line
of each waveform. Time in JLsec. per cm, given with pop
reading at the end of each waveform.
Terminal identification may not be found on unit.
Resistors are 'hW or less, 10% unless noted.
Value in ( ) used in some versions.
check IC Z59 by substitution. If pulses are missing at pin 9,
check IC Z25 by substitution.
If the Cassette Motor runs all the time, check for sticking
relay contacts and check for possible shorted Zener Diodes
CR9 and CRW.
If the Computer will not save programs onto tape, check for
the waveform shown in Figure 1at pin 2 of IC Z59. If the
waveform is present, check Resistors R53, R54 and R55 and
check pin 5 of Connector J3 for good connection. if the
waveform is missing at pin 2 of IC Z59, check for pulses at
pin 9 of IC Z59. If pulses are missing, check IC Z25 by
substitution. If pulses are present at pin 9 of IC Z59, check
IC Z59 by substitution.
If the Computer will not load aprogram from tape, connect
a 2V pop, 1kHz sinewave audio signal to pin 4 of Connector
J3. Type and run the following Basic program.
10 X= INT(255)
20 PRINT "X ="; X
30 OUT 255,0: GOTO 10
The number Xthat appears on the Monitor screen should be
255 when the 1kHz signal is injected at pin 4 of Connector
J3 and 127 with no signal injected. If the numbers are incor-
rect, check for pulses at pin 10 of IC Z4. If pulses are miss-
ing, check the voltages and components associated with
pins 1thru 14 of IC Z4.
If pulses are present at pin 10 of IC Z4 and the cassette
modification Counter IC (Z1C) and IC Z2C has been added,
check for pulses at pin 9of IC Z24. If pulses are missing at
pin 9, check Diodes CR200 and CR201, Resistor R200 and
check ICs Z1C and Z2C by substitution. If pulses are pres-
ent at pin 9of IC Z24, check for pulses at pins 8and 13 of IC
Z24 and pins 9and 10 of IC Z25. If pulses are missing from
pin 9 of IC Z25, check Tri-State Buffer IC (Z22), Micro-
processor IC (Z40) and ICs Z23 and Z52 by substitution. If
pulses are missing at pin 10 of IC Z25, check ICs Z36, Z52
and Z54 by substitution.
If pulses are present at pins 9and 10 of IC Z25 and missing
at pin 13 of IC Z24, check IC Z25 by substitution. If pulses
are present at pin 13 of IC Z24 and missing at pin 8 of IC Z24,
check IC Z24 by substitution.
If pulses are present at pin 8 of IC Z24, check for pulses at
pin 6 of IC Z25. If pulses are present at pin 6 of IC Z25,
check Tri-State Buffer IC (Z44) by substitution. If pulses are
missing at pin 6 of IC Z25, check for pulses at pin 4 of IC
Z25. If pulses are present at pin 4 of IC Z25, check IC Z25 by
substitution. If pulses are missing at pin 4 of IC Z25, check
ICs Z22, Z23, Z52 and Z40 by substitution.
If Relay K1 on the Expansion Interface Board is not oper-
ating, refer to the "Cassette" section of the Trouble-
shooting guide in the Expansion Interface Folder CSCS3-A.
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NOTE: Logic probe readings taken with computer in Power
Up mode (Main title screen displayed) unless other-
wise noted.
Logic Probe Display
L= Low
H = High
P= Pulse
'" =Open (no light on)
9