Tandy 1000SX User manual

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

giMflCCOMPUTERFACTS" TANDY
MODEL 1000SX
PRELIMINARY SERVICE CHECKS
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This data provides the user with atime-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 Iexternal peripherals from the
Computer system to eliminate possible external
ma Ifunctions.
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
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^ttb ^bb in ^Bt **s$^
mMMMlm 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 arecommendation, 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
aload.
5V ADJUSTMENT
12V ADJUSTMENT
NOTE: Perform the 5V Adjustment first. Con-
nect the Input of avoltmeter to pin 7of Con-
nector SK3-1. Adjust the 12V Adjust Control
for avoltage of 12.0V.
Connect the Input of avoltmeter to pin 9of
Connector SK3-1 .Adjust the 5V Adjust Control
(VR1) for avoltage 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
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(aamao)
B1 A1 B1 A1 81 Al B1 A1 B1 A1 J10B J10A
J15 J14 J13 J12 J11
J9
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(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
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(3C) (BE) R26A
VOLUME
U22 SYSTEM BOARD
LIGHT
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LOW, NORMAL,
HIGH, TURBO
51
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RESET
J8
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U55 ®
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U37 BE
U37A ®]
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RAM RAM
SP1
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JOYSTICK
PORTS
POWER SUPPLY
SK3-1
SK3-2
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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.
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COMPUTER DEAD
(A) Check for 5.0V at pin 1, -12.0V at
pin 8and 12.0V at pin 9of 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 1of Connector J6)
and a#93 lamp to the 12.0V Source
(Pin 9of Connector J6). WARNING:
Operating the Power Supply without
aload 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
atime 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) Aprogram runs for awhile, 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.
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(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 4of 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 akey
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 alogic 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 afrequency 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 Disk Dr ives
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 Idin
of chassis and I
i
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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.
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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 Interrupt 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 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 better to maintain asmoke-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 apower 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 aspill 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 acotton swab to clean between the keys. Use anon-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 amonth or after 100 hours usage.
Use only an approved head cleaning 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 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 alight 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 en-
vironment.
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 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 aboat* 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 aMS-DOS (Microsoft Disk
Operating System) diskette is used, the Com-
puter will display the date and time and ask
for anew 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 Awhich 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 adiskette Inserted
in Drive B.
MS-DOS
For alist 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 adiskette
while in DOS, type the program name and press
the ENTER key.
Ablank diskette must be formatted before It
can be used to save information which Is in
memory. Aformatted diskette must contain a
DOS or aStart-up program before the Computer
wll Iboot up using that diskette.
Insert adiskette 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 adiskette
will wipe out any programs previously placed
on the diskette. The Computer automatically
defaults to Disk Drive AIfthe 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 adiskette 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 alist 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 AIf it Is not the current (de-
fault) drive.
To load aprogram 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 aprogram, type SAVE, the program name
enclosed In quotes, and press the ENTER key.
To run aprogram from any Basic mode, type RUN
and press the ENTER key. To stop aprogram,
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 Ithree
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 Band Drive Bbecomes 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 aCPU speed
of 7.16MHz.
VOLUME CONTROL
AVolume 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
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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.aoa s ®e»a
»
Miscel laneous Adjustments.
Par*T slist......... .......
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 10, 12, 37, 39
Safety Precautions 14
Schematics 2thru 8, 42 thru 49
Schematic Notes 38
Switches and Jumpers 38
Test Equipment 15
Troubleshooting 15 thru 20
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PJPw« Howard W. Sams 4Co. 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 arecommendation, 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

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