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Tandy 3000

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Tandy 3000
Tandy 3000 HD (Radio Shack catalogue RSC-17, 1987)
A Tandy 3000 HD with a Tandy monitor and the 84-key keyboard, from Radio Shack's 1987 computer catalogue (Tandy copyright)
Specifications
ManufacturerTandy Corporation, sold by Radio Shack
TypeDesktop personal computer, IBM PC/AT compatible
Released1986
Intro priceUS$2,599 (catalogue RSC-16); US$2,199 in 1987
CPUIntel 80286, 8 MHz
Memory512 KB with parity, 640 KB on the main board; up to 12 MB with expansion cards
Storage1.2 MB 5.25-inch floppy drive; 20 or 40 MB hard disk on the 3000 HD
DisplayNone built in; monochrome or colour adapter card
SoundSpeaker
ROMBIOS in two 27128 EPROMs; four ROM sockets
FPU / coprocessorOptional Intel 80287 (socket on the main board)
Ports / interfaceParallel printer port and RS-232C on the standard serial/parallel card
ExpansionTen slots: seven 16-bit AT, two 8-bit XT and an 8-bit half slot for the serial/parallel card
Power120 V AC, 60 Hz
Dimensions6.5 x 19 x 18 in
Weight47 lb
OS / FirmwareMS-DOS 3.2 or XENIX System V (sold separately)
Model no.25-4001 (3000); 25-4010, 25-4011 (3000 HD)

The Tandy 3000 is an IBM PC/AT compatible desktop computer made by Tandy Corporation and sold through Radio Shack from 1986.[1] It uses an 8 MHz Intel 80286 with 512 KB of parity-checked RAM on the main logic board, has no video circuit of its own, and takes standard PC and AT expansion cards. Tandy's design specification describes it as compatible with IBM AT software in single-user MS-DOS, and as able to run a multi-user operating system in protected mode.[2] The Tandy 3000 HD is the same machine with a hard disk fitted at the factory.[3]

History

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Radio Shack's 1987 catalogue listed three versions:[3]

Tandy 3000 versions in catalogue RSC-17 (1987)
Catalogue no. Configuration Price
25-4001 Tandy 3000, 512 KB, one 1.2 MB floppy drive $2,199 (was $2,599 in catalogue RSC-16)
25-4010 Tandy 3000 HD, 512 KB, 20 MB hard disk $3,599
25-4011 Tandy 3000 HD, 640 KB, 40 MB hard disk $4,299

Monitor and video adapter were extra. MS-DOS 3.2 with BASIC and DeskMate II was catalogue 25-4103, and Tandy sold XENIX System V (25-4201) for running two to six users from one machine.[3]

Tandy 3000 12 MHz version 25-4002 (Radio Shack catalogue RSC-19, 1988)
The 12 MHz Tandy 3000 of 1988 (25-4002), with the 101-key keyboard and the keylock on the front panel (Radio Shack catalogue RSC-19).

In 1987 Tandy added the cheaper Tandy 3000 HL (25-4070), with a 4 or 8 MHz 80286, 512 KB, seven slots of which three are 16-bit, a 360 KB floppy drive and a smaller case (6⅛ x 17 x 15½ in, 32 lb).[4]In 1988 the Tandy 3000 itself was replaced by a 12 MHz version, catalogue 25-4002, at $1,999. It has 640 KB on the main board (expandable to 1 MB there), nine slots, the serial and parallel ports on the main logic board instead of a card, a 101-key keyboard and a keylock. Its listed power supply output is 192 W.[5] The 3000 NL followed in 1989.[1] These later models use different boards. Tandy's technical reference manual 25-4104 covers only the original 8 MHz machine.

Specifications

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Tandy 3000 (25-4001) from Tandy's design specification and catalogue
Item Detail
CPU Intel 80286 at 8 MHz (U77, 68-pin socket); clocks from an 82284 (U42) with a 16 MHz crystal (Y2)
Coprocessor Socket for an 80287
RAM 512 KB of 256K x 1 DRAM (eighteen TMS4256-15, 150 ns, at U117-U134), odd parity; 640 KB with a 128 KB upgrade in a second bank of eighteen sockets
ROM BIOS in two 27128 EPROMs (U59 and U61) in four sockets; jumpers allow 27256 parts
Expansion Ten slots; up to 12 MB of memory on expansion cards
Real-time clock Motorola MC146818 (U5) with battery backup
Keyboard 84 keys, AT compatible, 8049 microcontroller
Floppy drive 1.2 MB 5.25-inch slim-line drive (Mitsubishi M4854-3S or MF504A-3); reads 360 KB disks
Hard disk 20 or 40 MB on the 3000 HD; the manual's controller section is for a Western Digital WD1002-WA2 combined floppy and hard disk controller
Power 120 V AC, 60 Hz; 850 BTU/h heat output
Size and weight 6.5 x 19 x 18 in, 47 lb

Sources: Tandy's design specification and parts lists, and the 1987 catalogue.[2][6][7][3][8]

The sources disagree on the slots. The design specification counts ten slots, "2 PC compatible and 8 AT compatible".[2] The 1987 catalogue gives seven AT slots, two XT slots and an XT half slot for the serial/parallel adapter,[3] and the parts list has ten 62-pin connectors (J1-J10) but only seven 36-pin AT extension connectors (J12-J17 and J19), which matches the catalogue.[6]

Hardware

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Tandy 3000 main logic board power connector J23 and decoupling (schematic 8000265 sheet 13)
Sheet 13 of main logic board schematic 8000265: the 12-pin power connector J23 and the decoupling capacitor groups on the +5 V supply.

Main logic board

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The main logic board, PCB 8709635A, carries the processor, memory, the BIOS ROMs and the AT peripheral chips: two 8237A-5 DMA controllers, two 8259A interrupt controllers, an 8254-2 timer, an 8042 keyboard controller and the MC146818 clock.[6] Power arrives through J23, a 12-pin Mate-N-Lock connector: pins 1, 2, 4 and 5 carry +5 V, pin 3 +12 V, pins 6 to 9 ground, pin 10 −5 V, pin 11 −12 V and pin 12 Power Good.[9][6] The board has a jumper for colour or monochrome video, a trimmer for the colour burst clock, and jumpers for the ROM type and the RAM upgrade.[10] The scanned manual also lists a "Version 2" main logic board with its own schematic, 8000267, among the foldouts; those sheets are not in the scanned parts.[8]

Option cards

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The standard serial/parallel card (PCB 8709643B) sits in slot 10.[10][11] Floppy-only machines have Tandy's floppy disk controller board (PCB 8709672A), built round a uPD765 and a Western Digital WD16C92.[12] Tandy's memory expansion board takes 512 KB to 2 MB of 256K DRAM in 72 sockets and is set up with an eight-way DIP switch, whose table covers up to seven boards.[13]

Real-time clock and battery

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The MC146818 clock runs from the +5 V supply while the machine is on. Below about 3.0 V it switches to a battery connected through two diodes, CR1 and CR2, and Tandy gives the total drain with the machine off as 64.5 µA.[14] On the schematic the battery connects to J21, a four-pin header, with the positive lead on pin 1 and ground on pins 3 and 4.[15] The theory of operation calls it a lithium battery, and the chassis parts list names a 6 V battery assembly, Tandy part ACS-0020.[14][16]

Keyboard

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The keyboard has 84 keys and is driven by an 8049 microcontroller with a 6 MHz crystal. Its interface signals are clock, data, a spare line, ground and +5 V.[17] The main board's keyboard socket, J22, is listed as an 8-pin DIN connector.[6]

Known faults

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  • The machine keeps its setup in the battery-backed clock RAM, and setup is done from a program on floppy disk, not from a key at start-up. An owner of a 12 MHz Tandy 3000 reports that with a flat battery it gives a configuration error and needs Tandy's setup disk to configure it again.[18][19]
  • Battery leakage. One repairer working on a Tandy 3000 found that its battery had burst and damaged the corner of the main board nearest the drive cage, taking the markings off several parts.[20] Another owner describes the original battery as a 6 V pack attached to the side with hook-and-loop tape.[21] See Battery Explosion, Capacitor or Corrosion Damage.
  • A colour card gives no picture until the colour/monochrome jumper is moved from E2-E3 to E3-E4.[10]

The Tandy 3000 Troubleshooting Guide covers these in more detail.

Documentation

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  • Tandy 3000 Technical Reference Manual: Tandy's technical reference manual, catalogue 25-4104, hosted in three parts. It covers the main logic board, keyboard, memory board, serial/parallel card, floppy controller and 1.2 MB drive, with schematics and parts lists. The power supply, hard disk and BIOS sections are not in the scan.
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References

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  1. ↑ 1.0 1.1 "Tandy 3000", Wikipedia (retrieved 2026-10-21). Introduction in 1986; later HL and NL models.
  2. ↑ 2.0 2.1 2.2 Tandy Corporation, Tandy 3000 Technical Reference Manual, catalogue no. 25-4104, volume 1 part 1, hosted as File:Tandy 3000 Technical Reference Manual (25-4104), volume 1 part 1.pdf. Detail design specification, revision date 7 November 1985, pp. 1-5 (PDF pages 10-14): the four buses, product brief, 512 KB standard memory, ROM and RAM subsystems, parity, slots.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Radio Shack, Tandy Computer Catalog RSC-17, 1987, p. 4, "Tandy 3000 PC/AT-Compatible", scan at RadioShackCatalogs.com (retrieved 2026-10-21). Catalogue numbers and prices, specifications, slots, weight, dimensions and power requirement.
  4. ↑ Radio Shack, Tandy Computer Catalog RSC-17, 1987, p. 5, "3000 HL: 4 Times an XT's Power", scan at RadioShackCatalogs.com (retrieved 2026-10-21).
  5. ↑ Radio Shack, Tandy Computer Catalog RSC-19, 1988, p. 6, "Enhanced, 12-MHz Tandy 3000", scan at RadioShackCatalogs.com (retrieved 2026-10-21).
  6. ↑ 6.0 6.1 6.2 6.3 6.4 Tandy 3000 Technical Reference Manual (25-4104), part 1, main logic board parts lists, PDF pages 58-61: PCB 8709635A (10.9 x 16 in, four layers), capacitors, connectors J1-J25, integrated circuits and sockets, U59 and U61 27128 EPROMs, U77 80286-8, U117-U134 TMS4256-15NL.
  7. ↑ Tandy 3000 Technical Reference Manual (25-4104), part 1, theory of operation of the main logic board, 1.1 "Clock Circuits", p. 1 (PDF page 41).
  8. ↑ 8.0 8.1 Tandy 3000 Technical Reference Manual (25-4104), part 1, title page, table of contents and foldout insertion guide, PDF pages 1-6, listing the WD1002-WA2 FDC/HDC schematic, the 1.2 MB and 360 KB Mitsubishi drives and the power supply circuit diagram AA13260.
  9. ↑ Tandy 3000 Technical Reference Manual (25-4104), part 1, main logic board schematic D-8000265, sheet 13, "Option Board Connectors and Power Interface" (PDF page 76).
  10. ↑ 10.0 10.1 10.2 Tandy 3000 Technical Reference Manual (25-4104), part 1, theory of operation of the main logic board, section 6 "Upgrades, Jumper Settings and Alignments", pp. 14-17 (PDF pages 54-57).
  11. ↑ Tandy 3000 Technical Reference Manual (25-4104), volume 1 part 2, hosted as File:Tandy 3000 Technical Reference Manual (25-4104), volume 1 part 2.pdf. Serial/parallel option card: jumper settings, schematic and parts list (PDF pages 29-37).
  12. ↑ Tandy 3000 Technical Reference Manual (25-4104), part 2, floppy disk controller section, dated 15 November 1985: description, jumper settings, schematic, PAL equations and parts list (PDF pages 46-84).
  13. ↑ Tandy 3000 Technical Reference Manual (25-4104), part 2, 2 megabyte memory upgrade board: theory of operation, DIP switch settings (PDF page 10) and parts lists for revisions A and B (PDF pages 11-14).
  14. ↑ 14.0 14.1 Tandy 3000 Technical Reference Manual (25-4104), part 1, theory of operation of the main logic board, 4.4 "Real Time Clock", p. 8 (PDF page 48).
  15. ↑ Tandy 3000 Technical Reference Manual (25-4104), part 1, main logic board schematic D-8000265, sheet 11, "Interrupt Control and Real Time Clock" (PDF page 74).
  16. ↑ Tandy 3000 Technical Reference Manual (25-4104), part 1, "Tandy 3000 Chassis Subassembly" parts list (PDF page 62): 12 V DC fan assembly, speaker, floppy signal cable, battery assembly 6 V ACS-0020.
  17. ↑ Tandy 3000 Technical Reference Manual (25-4104), part 1, keyboard section, theory of operation (PDF page 86).
  18. ↑ "Trouble with Tandy 3000", Vintage Computer Federation Forums, December 2022 (retrieved 2026-10-21). Owner of a 12 MHz 25-4002 reports the configuration error with a dead battery, a "Drive 0 seek failure" and "No Boot Device Available", and that setup runs from a floppy disk program.
  19. ↑ "Tandy 3000 HD (no HD) issues", Vintage Computer Federation Forums, December 2019 (retrieved 2026-10-21). Two short beeps and no display; setup disk found on oldskool.org; advice to use the maker's own setup disk.
  20. ↑ "Tandy 3000 Rescue - Need Help!!", Vintage Computer Federation Forums, January 2022 (retrieved 2026-10-21). Battery explosion damaging the front right corner of the main board nearest the drive cage.
  21. ↑ "Tandy 3000 HD", Vintage Computer Federation Forums, March 2026 (retrieved 2026-10-21). Setup software and battery replacement; the battery was a 6 V pack attached to the side.


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