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Tandy 1000 HD General Maintenance

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Tandy 1000 HD Tandon TM250 drive board silkscreen (Service Manual p. 3)
Logic board of the Tandon hard disk in the Tandy 1000 HD, from the HD service supplement.

The Tandy 1000 HD shares its case, chassis and drive bays with the original Tandy 1000, so the case, keyboard and floppy work follows the Tandy 1000 maintenance guide. What is particular to the HD is the 10 MB Tandon TM252 hard disk and its Western Digital WD1002S-WX2 controller, which Tandy documents in a separate supplement.[1]

Opening the case

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Remove the case, rear panel and drive assembly as for the original 1000; the steps are in the Tandy 1000 guide.[2] The HD's chassis, drive support, option board panel and case top have the same part numbers as the 1000's.[3] To take out the hard disk controller, remove the screw at the rear wall and lift the card straight up, then unplug its two ribbon cables.[4]

Power supply

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The HD's main assembly list names a 54 W supply board with part number 8489073, where the original 1000 uses 8790070, and the supplement publishes no ratings or parts list for it.[3][5] Check the number on your supply before using the 8790070 figures. Whichever board is fitted, measure +12 V while the hard disk spins up: the TM252 draws 2.0 A typical and 2.4 A maximum on +12 V for up to 12 seconds at start, and Tandon allows +12 V within 10 percent.[6]

Hard disk care

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Back up the drive before any work on it. Tandon's notes for the TM252:[7]

  • Preventive maintenance: not required.
  • The heads are parked at cylinder 305 before shipment. Park them the same way before moving the machine; Tandon also advises parking before power-down.
  • The head and disk chamber is sealed and must not be opened.
  • Component design life is given as five years, with a mean time between failures of 11,000 power-on hours.

For general MFM drive care, see Hard Drive Maintenance and Repair.

Controller jumpers

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Jumper block SW1 on the WD1002S-WX2, next to the rear bracket, tells the controller which drives are connected. Its positions are marked 1 2 3 4 8 7 6 5 on the board. As shipped in the 1000 HD, positions 2, 3, 4 and 5 are jumpered; position 2 sets the internal drive as the 10 MB type with 306 cylinders and four heads, and positions 3 and 4 set the second drive type.[4] Note the settings before removing the card, and put them back the same way.

Low-level format and interleave

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The controller has a format routine in its ROM. A 1997 note in the TVDog archive reports that Tandy's HSECT.COM utility formats the drive at an interleave of 5, and that an interleave of 4 raised the measured transfer rate from about 100 KB/s to 124.6 KB/s; interleaves of 1 to 3 dropped it below 30 KB/s.[8] The note's method destroys everything on the drive:

  1. Back up every file.
  2. At the DOS prompt run DEBUG, set register AX to 0004 (the interleave) with r ax, and start the routine with g=C800:05. Answer "y" to the format prompt.
  3. Reformat the drive with HFORMAT (MS-DOS 2.11.22) or FORMAT under PC-DOS 2.10 or later.[8]

Floppy drive, keyboard and memory

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The floppy drive, keyboard and memory are handled as on the original 1000; see the Tandy 1000 guide. The HD came with 256 KB of memory as standard.[9]

Maintenance checklist

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  1. Back up the hard disk.
  2. Unplug the machine and open the case.
  3. Clean dust from the supply, fan, drives and slots.
  4. Note the SW1 jumpers and reseat the controller and its two ribbon cables.
  5. Check the supply board number and inspect it for damaged parts and cracked connector joints.
  6. Run the machine and measure +5 V and +12 V, including +12 V during hard disk spin-up.
  7. Park the heads before moving the machine.
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References

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  1. ↑ Radio Shack, Tandy 1000 HD Service Manual, catalogue no. 25-1001, Tandy Corporation, 1986, hosted as File:Tandy 1000 HD Service Manual (25-1001, 1986).pdf.
  2. ↑ Radio Shack, Service Manual: Tandy 1000 Computer, catalogue no. 25-1000, 1985, hosted as File:Tandy 1000 Service Manual (25-1000, 1985).pdf. Section 3 "Disassembly-Assembly", pp. 5-6.
  3. ↑ 3.0 3.1 Tandy 1000 HD Service Manual (25-1001), "Tandy 1001 Main Logic Main Assembly", p. 31.
  4. ↑ 4.0 4.1 "Adding a second (external) hard drive to the Tandy 1000HD", t1khd.txt, TVDog's Tandy 1000 archive (retrieved 2026-10-21).
  5. ↑ Tandy 1000 Service Manual (25-1000), "Parts List, 54 Watt Power Supply 8790070", p. 100.
  6. ↑ Tandon Corporation, TM252 Rigid Disk Drive product specification, document 179050-001 Rev. B, Table 2.1, "Power Requirements", p. 2-2, reprinted in the Tandy 1000 HD Service Manual (25-1001).
  7. ↑ Tandon, TM252 specification (179050-001 Rev. B), Table 2.1 and p. 2-6, reprinted in the Tandy 1000 HD Service Manual (25-1001).
  8. ↑ 8.0 8.1 "Tandy 1000HD Hard Disk SpeedUp", hdisinf.txt, TVDog's Tandy 1000 archive (retrieved 2026-10-21). Author not recorded in the file.
  9. ↑ Jeff Hayes, "models.txt", TVDog's Tandy 1000 archive, 2005 (retrieved 2026-10-21).


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