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Tandy 5000 MC General Maintenance

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Tandy 5000 MC exploded view (Tandy drawing via Ardent Tool)
Tandy's exploded view of the 5000 MC: top cover, rear panel and cover mounting screws, power supply, main logic board, and the CPU and memory boards.

Routine care of the Tandy 5000 MC is mostly about its configuration memory, which lives in two Dallas modules with built-in lithium cells, and about the memory cards, which are set with DIP switches and jumpers. Tandy's technical reference for the machine has not been found online. What follows comes from Radio Shack's faxback service documents and the board notes collected by Ardent Tool of Capitalism, with owners' reports where named.[1]

Opening the case

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The front panel has a key lock that stops the case being opened when locked.[2] Tandy's exploded view shows the top cover lifting off once the cover mounting screws at the rear have been removed, with the CPU and memory boards standing upright above the main logic board.[3]

  1. Unlock the case and unplug the mains lead and all cables.
  2. Remove the cover mounting screws at the rear and lift the top cover off.
  3. Before removing any card, note its slot; the reference diskette identifies Micro Channel cards by slot.

Configuration memory

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The 5000 MC keeps its configuration in battery-backed CMOS memory, written by the reference diskette.[4] There is no separate battery. The parts concerned are:

Battery-backed parts on the main logic board
Position Part Radio Shack part no.
U19 Dallas DS1287A real-time clock with CMOS RAM MX-1561
U11 Dallas DS1220Y 2K x 8 non-volatile RAM MX-1560

Sources: Radio Shack's specification sheet and Ardent Tool's board notes. Radio Shack's sheet calls both "CMS battery clock chip"; the parts list gives U11 as a DS1220A.[5][1][6] Each Dallas module has its own lithium cell; Dallas rated the DS1287 for more than ten years without power and the DS1220Y for at least ten years of data retention.[7][8]

  1. Make a working copy of the reference diskette first. Ardent Tool hosts an image of version 1.02.03.[1]
  2. If the machine still holds its settings, run Backup Configuration from the reference diskette to save them to the working copy.[4]
  3. Replace the DS1287A and the DS1220Y with new modules.
  4. Start from the reference diskette and use Restore Configuration, or run Automatic Configuration, then set the date and time.[4]

The CMOS clear jumper is E1-E2; Radio Shack's settings sheet marks it "do not use" and the factory setting is off. E3-E4 and E5 to E8 should have no jumpers.[9]

Adding or changing an expansion card

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Whenever a Micro Channel card is added or removed, copy the card's adapter description files to the working reference diskette with Install New Adapter Files, then run Automatic Configuration. View Configuration marks conflicting settings with an asterisk.[4] BYTE found that the 5000 MC noticed a new card at start-up and asked for the reference diskette, which then configured it.[10]

Memory

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Memory goes on Tandy's 32-bit memory cards (catalogue 25-6030), each with eight SIMM sockets. A card takes 2 MB in 256K x 9 SIMMs or 8 MB in 1M x 9 SIMMs, and all SIMMs on the memory bus must be of one size.[11][12] After changing memory, set the main board switches and jumpers:

Memory settings (Radio Shack faxback 1722 and 1723)
Memory S1 on (others off) S2 on (others off) Jumpers
2 MB (factory) 4 1, 4, 8 E9-E10, E11-E12, E14-E15, E16-E17
4 MB 3, 4 4, 8 E9-E10, E11-E12, E14-E15, E16-E17
8 MB 4, 6 1, 4 E9-E11, E10-E12, E14-E16, E15-E17
16 MB 3, 4, 6 4 E9-E10, E11-E12, E14-E15, E16-E17

Radio Shack's 16 MB recipe is a second 25-6030 card, with 1 MB SIMMs (kit 25-5137) on both cards.[12] Ardent Tool's notes add that S2 switch 8 selects 256K (on) or 1 MB (off) SIMMs and that, because memory is interleaved, all eight sockets on a card should be filled; Ardent marks these as its own deductions.[1]

Coprocessor

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Radio Shack's coprocessor sheet says the 80387 plugs into socket U2.[13] The sheet calls U2 a main logic board position, but Ardent Tool's notes place U2 (80387DX-20) on the CPU card; on the main board U2 is the 8742 keyboard controller.[1] Look on the CPU card first. Use a 20 MHz 80387.[5]

Floppy drive

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The floppy controller supports 360K, 720K, 1.2 MB and 1.44 MB drives, but not 2.88 MB.[1] On the 34-pin floppy header, pins 5, 7, 9 and 11 carry +5 V to the 3.5-inch drive; Radio Shack notes that this +5 V is not available to a 5.25-inch drive.[14] Check the cable and drive before fitting a drive from another machine. For cleaning and general drive care see Floppy Drive Repair.

Capacitors

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The Tandy 5000 MC Capacitor Replacement Guide lists what Radio Shack's parts lists give. See also Capacitor Failure Symptoms.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 "Tandy 5000 MC", Ardent Tool of Capitalism (retrieved 2026-10-21). Main logic board 8899061 layout and parts, CPU and memory boards, power connector J7, switch notes, floppy controller support, copies of Radio Shack faxback documents.
  2. ↑ "Tandy 5000 MC", Wikipedia (retrieved 2026-10-21), citing PC Magazine, 28 March 1989: intrusion key lock on the front panel; reset button recessed behind the front trim.
  3. ↑ File:Tandy 5000 MC exploded view (Tandy drawing via Ardent Tool).png: Tandy's exploded view of the system unit, from Ardent Tool.
  4. ↑ 4.0 4.1 4.2 4.3 Radio Shack faxback document 1724, "5000 MC Utility: The Reference Diskette", copy at Ardent Tool (retrieved 2026-10-21).
  5. ↑ 5.0 5.1 Radio Shack faxback document 1721, "5000 MC (250-6000/1/2) Specifications", copy at Ardent Tool (retrieved 2026-10-21). Battery replacement: MX-1560 (U11), MX-1561 (U19).
  6. ↑ Radio Shack faxback document 22041, "250-6000 Tandy 5000 MC" detailed parts list, copy at Ardent Tool (retrieved 2026-10-21).
  7. ↑ Dallas Semiconductor, DS1287 Real Time Clock data sheet, copy at Ardent Tool (retrieved 2026-10-22), page 1.
  8. ↑ Dallas Semiconductor, DS1220Y 16K Nonvolatile SRAM data sheet, copy at Ardent Tool (retrieved 2026-10-22), page 1.
  9. ↑ Radio Shack faxback document 1722, "5000 MC Settings", copy at Ardent Tool (retrieved 2026-10-21).
  10. ↑ Mark L. Van Name, "A PS/2 in Channel Only", BYTE, February 1989, pp. 197-202, scan at the Internet Archive.
  11. ↑ Eric Knorr, "Tandy 5000MC", The Hardware Shelf, PC World, April 1989, pp. 102-106, scan at the Internet Archive.
  12. ↑ 12.0 12.1 Radio Shack faxback document 1723, "5000MC Memory", copy at Ardent Tool (retrieved 2026-10-21). SIMM kits and part numbers, memory board 25-6030, switch and jumper tables.
  13. ↑ Radio Shack faxback document 1727, "5000 MC Math Co-processor", copy at Ardent Tool (retrieved 2026-10-21).
  14. ↑ Radio Shack faxback document 1725, "5000 MC Pinouts", copy at Ardent Tool (retrieved 2026-10-21).


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