Tandy 1000SX Technical Service Data

HOWARD

W. SAMS

&

COMPANY

COMPUTERFACTS

Technical

Service Data

TANDY®

MODEL

1000SX

COMPUTER

FEATURES COMPLETE

SCHEMATICS •

PRELIMINARY

SERVICE CHECKS

•

TROUBLESHOOTING

TIPS

EASY-READ

WAVEFORMS

•

REPLACEMENT

PARTS

LISTS •

SEMICONDUCTOR CROSS REFERENCE

giMflC

COMPUTERFACTS"

TANDY

MODEL

1000SX

PRELIMINARY

SERVICE CHECKS

x

ca

o

v.

O

Q

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uj

I-

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o

s

o

This

data

provides the user with a

time-saving

service

tool

which is

designed for quick

Isola-

tion and repair

of Computer

system malfunc-

tions.

Check all

interconnecting cables for

good con-

nection

and correct hook-up

before making

service checks.

Always

turn

the

Computer Off before connecting

or disconnecting

connectors,

boards or

periph-

erals.

Disconnect al

I

external peripherals

from the

Computer system to

eliminate possible external

ma I functions.

Replacement or repair of the

Power Supply,

System Board, Keyboard, Disk Drives or

con-

nectors

may

be

necessary after the

malfunction

has been isolated.

TEST EQUIPMENT

AND

TOOLS

TEST EQUIPMENMT

Digital Volt/Ohm Meter

Logic

Probe

Frequency

Counter

Monitor with Audio Input

Disk Drive Tester or Test

Program

TOOLS

Head Cleaning

Equipment

Contact and Switch

Cleaner (non-spray type)

Phillips

Screwdriver

Flat Blade Screwdriver

1/4"

Socket

IC

Insertion and Removal Tools 20,

24 and 40

14,

16,

28

Low Wattage

Soldering Iron

Deso

I

der

i

ng

Eq

u

I

pme nt

^ttb ^bb in ^Bt

**s$^

m MMMlm

Howard

W. Saras

&

Co.

'm

4300 West 62nd Street,

P.O. Box 7092, Indianapolis, Indiana

46206 U.S.A.

The fisting

of

any

available replacement part herein

does not

constitute in any

case a

recommendation, warranty

or guaranty

by Howard W. Sams

& Co. as to

the quality

and suitability of

such replacement part. The numbers of

these parts have been

compiled from information furnished

to Howard W. Sams

& Co.

by the manufacturers of the particular

type of replacement part

listed.

87CS19008

DATE

9-87

Reproduction or

use,

without express permission, of editorial

or

pic-

torial content, in any manner, is prohibited. No patent liability is

assumed with

respect to

the

use

of the information contained herein.

Co.

4300

West

62nd

Street, P.O. Box 7092,

Indianapolis, Indiana

46206

U.S.A.

Printed in U.S. of America

MISCELLANEOUS ADJUSTMENTS

POWER

SUPPLY

NOTE:

Do

not operate

the Power

Supply

without

a load.

5V ADJUSTMENT

12V

ADJUSTMENT

NOTE:

Perform

the 5V

Adjustment

first.

Con-

nect the

Input

of a voltmeter

to pin 7

of Con-

nector

SK3-1.

Adjust

the 12V

Adjust

Control

for

a voltage

of 12.0V.

Connect

the

Input

of

a voltmeter

to

pin 9

of

Connector SK3-1

.

Adjust

the

5V

Adjust

Control

(VR1)

for a voltage

of 5.0V.

VR1

VR2

5V

12V

ADJUST

F1

:ib.

CN

(3B)

KEYBOARD

INTERCONNECTING

DIAGRAM

II

PRELIMINARY

SERVICE CHECKS

(Continued)

UAj

v

-^

COMPOSITE

AUDIO VIDEO

RGB

VIDEO

/

*

' * *

\

(

a a

m

a

o

)

B1

A1

B1

A1

81

Al B1

A1 B1 A1

J10B J10A

J15

J14 J13

J12 J11

J9

S.OV©

1

t

. .

.

(8B)

4.77MHz,N0RMAL

7.16MHz,TURB0

J6

12

U51

B31

A31

B31

A31 B31

A31 B31 A31

831

A31

®

SEE

SWITCHES

S2 AND JUMPERS'"

U41

ROM (1D)

VIDEO SYSTEM (4C)

RAM 128K

v^

U3B

CPU

®

U35

3EU

E4F^lE3

U24

]

P

5

i

SB)

(3C) (BE)

R26A

VOLUME

U22

SYSTEM

BOARD

LIGHT

PEN

*ezz3'.

Y

LOW, NORMAL,

HIGH, TURBO

51

~EJ-

J4

J3

J2

RESET

J8

©

u

J7

33

E6

E5

U55

®

J5

U37

BE

U37A

®]

2A)

BANK

1

BANK

2SBK 25SK

RAM

SP1

8a Z

*!©

JOYSTICK

PORTS

POWER

SUPPLY

SK3-1

SK3-2

SK2

©

(Ta) VR2

LD

VR1

5V ADJUST

(IB)

F1

v

-'

250V

3A

<J\P

SKI

6C

(£2)

i—n

sv

J2

l§

(SB)

1

s

2 6

J4

12

J9

2

11

J3

1

(SB)

|

6 J5

1

|

m

R1

(£)

U

L

1

4

J7

DISK DRIVE

A

BOTTOM VIEW

SI

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.001 T

120VAC

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380BA

J1

11

2

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J2

S§

6B

1

s

2 S

J4

12

J9

2

11

J3

1

TP8Q

I

6

J5

1

R1

(Si

L_r

1

4

J7

DISK DRIVE

B

BOTTOM VIEW

TANDY

MODEL

1000SX

INTERCONNECTING

DIAGRAM

PRELIMINARY

SERVICE

CHECKS

(Continued)

LOW.

NORMAL

HIGH, TURBO

J4

R26A

J1

RAM

BANK1

BANKO

VI

III

PRELIMINARY

SERVICE

CHECKS

(Continued)

SERVICE

CHECKS

MATCH THE

NUMBERS ON THE

INTERCONNECTING

DIAGRAM AND

PHOTOS

WITH

THE

NUMBERS

ON THE SERVICE

CHECKS TO

BE

PERFORMED.

©

COMPUTER DEAD

(A) Check for

5.0V

at pin

1,

-12.0V

at

8

and 12.0V at pin

9

of Connec-

tor J6 on

the System

Board.

If the

voltages are correct, go to

part

(D).

If

the voltages are not cor-

rect, check the adjustment of the

5V Adjust (VR1) and 12.0V Adjust

(VR2) Controls on the

Power

Supply

Board,

see "Mi seel laneous Adjust-

ments."

(B) If the voltages are

missing

at Con-

nector

J6, turn the Computer Off

and disconnect the power connectors

from

the System Board and Disk

Drive.

Connect a

#1129 lamp

to the

5.0V Source (pin 1 of Connector

J6)

and

a

#93 lamp to the 12.0V Source

(Pin 9 of Connector

J6). WARNING:

Operating the

Power

Supply without

a load

may damage

it. Turn the

Power Supply On and

recheck

the

voltages.

If

the voltages are

still

missing, check

Fuse F1

.

(C) If the correct voltages return, re-

connect the

Power

Supply

to the

System Board and Disk

Drives

one at

a time until the Board or Drive

that

is

causing the Power

Supply to

shutdown

is

found. WARNING: Be

sure

Power

supply is

turned Off

when connecting to the System Board

or Disk Drive.

(D)

Check the

CPU

IC (U36)

and ROM IC

(U41) by

substitution.

SYSTEM BOARD

(A)

A

program runs for a while, then

suddenly stops or becomes

erratic

in operation. Check RAM

IC

Banks

and

1 (IC's

U1 thru U16).

KEYBOARD

(A)

Keyboard dead. Check Connector J4

on the System

Board

for

good connec-

tions.

(B) Check the Keyboard cable and check

Connector CN on the Keyboard for

good connections.

(C)

Check IC U22

on the System Board by

substitution.

VIDEO

(A) No video. Check Connectors J9 and

J10A for good connections and

check

the

Video cable

going to

the Mon-

itor.

©

(B)

(C)

Check Video

tion.

IC

(U30) by

substltu-

Video display

is

not correct.

Check Video

IC (U30) and Video RAM

IC's

(U24,

U31, U34 and U35).

SOUND

(A) No sound from the Internal Speaker

(SP1) and

no audio at Connector

J10B. Check IC U37A by substitu-

tion.

(B) No sound from the Internal

Speaker

(SP1).

Check the setting

of the

Volume Control

(R26A) on the System

Board.

(C) If

Volume Control is set properly,

check Connector

J1 on System

Board

for good

connections and check

Speaker (SP1) voice coil for conti-

nuity.

DISK

DRIVE

(A) Disk Drive operation Is

erratic.

Clean

the

Drive

heads.

Check the

Drive Spindle

Speed, see "Spindle

Speed

Check".

(B) Check

Connectors J1, J2, J4 thru

J7

and J9

on

the Disk

Drive and Connec-

tor J5

on the System Board for

good

connections.

(C) Drive dead. Check for 12V at

1

and 5V

at pin

4

of Connector J2 on

the Drive Board.

If

the

voltages

are missing, check the Power

Sup-

ply.

CD)

If the voltages are

present

at Con-

nector J2, check the setting of

Switch S2-3 on the System Board.

It

should

be

set

On.

(E) If Switch S2-3

is set On,

check

IC's U22

and

U37 on the System

Board

by

substitution.

PARALLEL

PORT

(A) Paral

lei

Port

does not work, check

Connector J7

for good connections.

(B) Check

IC U55 by

substitution.

IV

PRELIMINARY SERVICE

CHECKS

(Continued)

(D

NORMAL/TURBO CPU

CLOCK

(A)

Run the

following

program to

switch

the CPU

clock speed

each time

a

key

is pressed:

10 OUT 98,32:PRINT

"NORMAL

(4.77MHz)"

20

AS=!NKEYS:IF

AS=""

THEN 20

30 OUT 98,40:PRINT

"TURBO

(7.16MHz)"

40 AS=INKEYS:IF

AS="" THEN 40

ELSE 10

Check

for a logic

Low at

pin 37

of

IC U22

with

the speed

set

to "Nor-

mal"

and logic High

with

the

speed

set to "Turbo".

if the

reading

is

not correct,

check IC

U22.

(B)

Check

for

a frequency

of

4.77MHz

at

pin 16

of

IC U51 with

the

speed

set

to

"Normal"

and

7.16MHz

with

the

speed set

to

"Turbo". If

the

fre-

quency does

not

switch,

check

IC

U51.

CABINET

REMOVAL

DISASSEMBLY

INSTRUCTIONS

SYSTEM

BOARD

REMOVAL

Remove

two screws from lower

front

of cabinet.

Slide cabinet forward

and up

to

remove.

REAR

PANEL REMOVAL

Remove three screws from lower rear of rear

panel.

Pull

out

on

bottom

of

panel

and lift

up

to

clear

tabs on top

to remove panel.

DISK DRIVE REMOVAL

Slide

metal

shield out of

slot on

left

side of

Disk Drive

bracket.

Remove

two screws

from

left front, two

screws from

left rear

and one

screw from right

bottom

of Disk

Drive

bracket.

Slide

the Drives forward

and

unplug

four con-

nectors from

rear

of Drives.

Remove Drives

from

Main Chassis.

Remove

four

screws from

right side and two screws

from left side

of

Disk

Drive bracket

to remove Drives

from

bracket.

POWER

SUPPLY

REMOVAL

Unplug

Power

Supply Connectors from

System

Board and Disk Drives.

Remove rear

panel.

Remove four screws

from rear holding

Power

Supply

to chassis

and lift Power Supply

out

of

chassis.

Remove

D

i sk Dr

i

ves

four

screws

holding

remove

left

side,

from

System Board.

and

Power

left

side

Supply. Remove

of

chassis

and

System

Board.

System

Board

to bottom

board

out

of

chassis.

POWER

SUPPLY DISASSEMBLY

Disconnect Speaker

Remove

plug- in

boards

plug

from

Remove

four screws

ho

I din

of chassis

and

I

i

?f

Remove

four screws

holding

Fan.

Unplug

and

remove Fan. Grip

end

of

chassis

Power

Connector,

pull

out

to

clear the tabs,

disconnect Connector

SKI

and

remove the end

of

chassis with On-Off

Switch

and

AC Connector.

Remove

four

screws

holding

board

to chassis

and

remove board.

KEYBOARD

DISASSEMBLY

Remove nine

screws

from bottom

of

Keyboard

cabinet

and

remove

bottom

of

cabinet.

Lift

Keyboard

out of cabinet

top.

s

o

m

is,

r-

=;

<

X

SWITCHES

AND

JUMPERS

SYSTEM BOARD

VIDEO AND INTERRUPT

SWITCHES (S2)

ON

OFF

S2-1

Video

S2-2 Vertical Sync

S2-3 Floppy Disk Controller

S2-4

Parral

lei

Port

Color

Graphics Video

(Internal

or

optional

CGA Board)

Enab ie Interrupt 5

Enab Ie

I nterrupt

6

Enable Interrupt 7

Optional

Monochrome

Video Board

Disable Interrupt

5

Disab

Ie

Interrupt

6

Disable Interrupt

7

RAM JUMPER

Remove

jumper from pins El

and

E2 when

installing

additonal 256K

RAM IC's.

(U5 thru U8 and U13 thru U16.5

8047 MATH

CO-PROCESSOR JUMPER

Remove

jumper from pins E3

and E4 when

installing

on 8047

Math Co-Processor

IC

(U33).

PRELIMINARY

SERVICE

CHECKS

(Continued)

LOW.

NORMAL

HIGH, TURBO

J4

R26A

J1

RAM

BANK1

BANKO

VI

III

PRELIMINARY

SERVICE CHECKS

(Continued)

PREVENTATIVE MAINTENANCE

ENVIRONMENT

Computers perform best in a clean,

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 better to

maintain a

smoke-free area

around the Computer. Do

not block cabinet

vents of 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. A

power-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

cotton swab to

clean between the keys. Use a

non-abrasive contact

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 cleaning kit.

Handle

carefully

to

preserve

proper disk head alignment. A

sudden bump or jolt to

the Disk

Drives can knock

the disk head out

of alignment. If 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

a

blanket. 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 en-

vironment.

MONITOR

Use an

isolation transformer

with any Monitor that does

not come

as

part of the system

since

some Monitors use a

HOT chassis

(chassis connected to one side

of the

AC

line). The

face of

the Monitor should never be

left on for long period 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.

VII

r:-fc^ Pi

SERVICE

CHECKS (Continued)

GH

"

:

"

>ERATING

INS

',-UCTIONS

BOOT UP

insert a boat*

le diskette Into

Disk

Drive

A

and turn

On

the

Computer. The

Computer

will

automatically boot up using

the diskette

In

Disk Drive

A.

If

a

MS-DOS (Microsoft

Disk

Operating

System)

diskette is

used, the

Com-

puter will display

the

date

and time

and

ask

for a new

date and time.

After

the date and

time have been entered, the version

of

DOS

will

be

displayed on the Monitor screen

along

with

an A

which

indicates the

DOS

is

run-

ning.

If Function Key

F3 is pressed immediately

after the Computer beeps when turned On,

the

Computer will boot

up

from

a

diskette Inserted

in Drive B.

MS-DOS

For

a

list of file

names on

the

diskette fn

the

current

Disk Drive,

type

DIR

and press

the

ENTER

key.

To specify Disk Drive that is not

current (default),

use

DIR A:

for Disk Drive A

or

DIR B:

for

Disk Drive

8.

To return

to

MS-DOS

from Basic, type SYSTEM

and press

the ENTER

key.

To load

a

(System) program from a

diskette

while

in DOS,

type

the program name and

press

the ENTER key.

A

blank diskette must

be

formatted before

It

can be used

to save information

which Is

in

memory. A formatted diskette

must contain

a

DOS

or a Start-up program before the Computer

wll I boot up using

that diskette.

Insert a diskette containing

a "Format Pro-

gram" into

Disk

Drive A. Type

FORMAT

and

press

the

ENTER

key. Follow

the instructions

on the Monitor screen to

'format the unformat-

ted diskette.

NOTE: Formatting a

diskette

will wipe out any

programs

previously

placed

on the diskette. The Computer

automatically

defaults to Disk

Drive A I f

the destination

Disk

Drive is not

specified. Be sure to spec-

ify the

destination Disk Drive

of the diskette

to be

formatted or

the original diskette may

be

ruined

by the default action.

BASIC

When turned On, the Computer will

come

up

In

MS-DOS

as long as the MS-DOS diskette

Is

in

Drive A.

The version

of

MS-DOS will

appear at

the

top of the screen.

The manufacturer

also supplies Disk Basic

on

diskette.

To load Disk Basic,

first boot up

DOS.

Insert

a diskette with Disk Basic

pro-

gram

on it. Type

BASIC and press

the RETURN

key or

type

BASICA

and press the

RETURN key

to

load Disk Basic. To

return

to

DOS from Basic,

type SYSTEM and press

the ENTER key.

To

view

a list and the

names of

programs

on a

diskette In the

current Drive, type

FILES

and

press the ENTER key.

Type

FILES "Bs

*•*"

and

press

the

ENTER

key

to

list programs

from Disk

Drive B. Type

FILES

"A:

*.*"

to

list

programs

from Disk

Drive A If

it

Is not the

current (de-

fault)

drive.

To load a

program

in Disk Basic

or

Advanced

Disk Basic

from the

diskette,

type

LOAD, the

program name enclosed

in quotes,

and press the

Enter Key.

To

save a program, type SAVE, the

program name

enclosed

In quotes, and

press

the

ENTER key.

To run

a

program from

any Basic

mode, type RUN

and press the ENTER

key. To stop

a program,

press the CTRL and BREAK

(SCROLL

LOCK) keys at

the same

time. NOTE:

Some

programs will

dis-

able

or not recognize

the

CTRL and

BREAK

keys

to prevent the user stopping the program while

it

is running.

RESETTING

COMPUTER

Press the CTRL, ALT, and DEL keys, al

I

three

at the same time, to reset the Computer. The

Computer

can also be reset by

pressing

the

Reset button on lower left front panel.

CHANGING OPERATING

MODES

The

Video, Disk Drive, and

CPU

speed

modes

can

be changed

by

pressing

Function Keys

F1

thru

F4

immediately after the Computer beeps when

it

is

turned On. Use the following chart to

determine

the

function

of

each Key:

F1

-

Changes the Video mode

to

Monochrome

node.

(Computer normally comes up

In

Color

Graphics

mode.)

F2

-

Changes the Video mode

to

TV mode.

F3

-

Swaps Disk

Drive

references.

Drive

A

becomes Drive B and Drive B becomes Drive

A. The Computer

will

boot

up

from the

top

Drive

(normally Drive

B).

F4

-

Changes

CPU

speed to

4.77MHz. The Com-

puter normal ly comes up with

a CPU speed

of

7.16MHz.

VOLUME CONTROL

A

Volume

Control

(R26A)

is

provided on the

Main

System Board

to set the

volume

of

the

In-

ternal

speaker. The cabinet must

be

removed

to gain access to the control.

VII!

PRELIMINARY

SERVICE

CHECKS (Continued)

CHASSIS

BOTTOM

VIEW

HEADS

SPINDLE

mk

CHASSIS TOP VIEW

IX

5j*/M5

COMPL'TERFACTS

TANDY

MODEL

1000SX

SYSTEM BOARD,

KEYBOARD,

POWER

SUPPLY

x

m

©

>-

o

<

UJ

J_

Q

o

s

5

o

m

o

SAFETY

PRECAUTIONS

See

page 1

4

INDEX

Block

Diagram.

Disassembly

Instructions

General Operating

Instructions...

GridTrace

Location Guide

Power Supply

Board

System

Board

IC

Pinouts

and Terminal Gu

Line Definitions.....

LOgiC

ChartS®

. . e .

a o a s ® e »

a

»

Miscel laneous Adjustments.

Pa

r*T s list.........

.......

ides.

.30

th

,.21

th

Page

.

41

, 14

.

13

,

29

, 11

.9,40

.

34

ru 33

38

ru 27

Page

Photos

Keyboard

36

Power Supply

Board 28,35

System Board 1

0,

1

2,

37,

39

Safety

Precautions

14

Schematics

2

thru

8,

42 thru

49

Schematic Notes

38

Switches

and Jumpers

38

Test

Equipment

15

Troubleshooting

15 thru

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Howard W. Sams

4

Co.

4300 West 62nd Street, P.O. Box

7092,

Indianapolis, Indiana 46206 U.S.A.

The listing of any available

replacement

part herein does not

constitute in any

case a

recommendation, warranty or guaranty

by

Howard

W.

Sams

& Co. as to

the quality and suitability of

such replacement part. The

numbers of these parts have been

compiled from information furnished to Howard W. Sams & Co.

by the manufacturers of the particular type of

replacement part

listed.

87CS19008

DATE

9-87

Reproduction or

use,

without

express permission, of

editorial or pic-

torial

content,

in any manner,

is prohibited. No patent liability

is

assumed

with

respect to

the use

of the information contained

herein.

Howard W.

Sams

&

Co.

4300

West

62nd Street,

P.O. Box 7092,

Indianapolis, Indiana 46206

U.S.A.

Printed in

U.S.

of America

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1987

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Tandy 1000SX Technical Service Data

Tandy 1000SX Technical Service Data

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