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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
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O
Q
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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
pin
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.
© 1987 Howard W. Sams &
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
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
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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J1
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J2
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6B
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J4
12
J9
2
11
J3
1
TP8Q
I
6
J5
1
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
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
pin
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
pin
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
next
to AC
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
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 »
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Miscel laneous Adjustments.
Pa
r*T s list.........
.......
ides.
.30
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th
Page
.
41
, 14
.
13
,
29
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.
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
20
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Howard W. Sams
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Co.
4300 West 62nd Street, P.O. Box
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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.
© 1987
Howard W.
Sams
&
Co.
4300
West
62nd Street,
P.O. Box 7092,
Indianapolis, Indiana 46206
U.S.A.
Printed in
U.S.
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