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Tandy 1000 HX General Maintenance

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Tandy 1000 HX opened with replacement fan (Blake Patterson)
A Tandy 1000 HX with the top case off: keyboard at the front, supply at the left and a replacement fan (photo: Blake Patterson, CC BY 2.0).

Routine care of the Tandy 1000 HX covers the power supply and fan, the 3.5-inch drives that draw power through the data cable, the built-in keyboard, memory expansion and the EEPROM settings. No HX service manual has been found. The power supply figures below come from the Tandy 1000 EX technical reference manual, because the HX supply carries the same transformer and part references as the EX's 28 W supply 8790083.[1][2]

[1]

Opening the case

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The FAQ describes the EX and HX as awkward to take apart.[3] Photograph each cable before unplugging it. On the EX, the keyboard joins the main board through two flat flexible cables in zero-insertion-force connectors; open the latch before pulling a cable and seat the cable fully before closing it.[4]

Power supply and fan

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Measure +5 V, +12 V and -12 V with the machine running and compare them with the EX supply's limits:[1]

28 W supply operating characteristics (EX manual)
Output Minimum Typical Maximum Load range
+5 V 4.85 V 5.00 V 5.15 V 1.25-3.0 A
+12 V 11.40 V 12.00 V 12.60 V 0.1-1.25 A
-12 V -13.20 V -12.00 V -10.80 V 0-0.1 A

If the supply is out of the machine, load it before switching on; the EX manual warns that it must never run without a load.[1] The full procedure is on Tandy 1000 EX Troubleshooting Guide.

Keep the fan running freely. One owner reports that the HX fan is a 60 mm part, and another fitted a replacement fan after a clean-up.[5][6] Check the size of the old fan before ordering.

Floppy drives

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The HX's 3.5-inch drives take power through the data cable: +5 V on pins 3, 5, 7, 9 and 11 and +12 V on pins 29, 31 and 33, which are ground pins on a standard drive.[7]

  • Replace a drive only with another Tandy-style drive, or modify the cable as the FAQ describes. A standard drive on the unmodified cable can damage the drive and the computer.[7]
  • The cable is straight, not twisted; each drive's select jumper sets A: or B:.[7]
  • After a DOS upgrade, a 720 KB drive may format disks as 360 KB. The FAQ's fix is a DRIVPARM line in CONFIG.SYS, for drive A: DRIVPARM=/D:0 /F:2 /H:2 /S:9 /T:80.[8]
  • The external drive port takes Tandy's 360 KB (25-1060) or 720 KB (25-1061) external drives.[9]

General cleaning is covered on Floppy Drive Repair.

Keyboard

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The keyboard is built in. A failed keyboard can only be replaced from another EX or HX.[3]

Memory, expansion and storage

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  • The HX has 256 KB. More memory comes on a PLUS memory card made for the EX and HX, which also carries the DMA controller a hard disk controller needs.[10] The EX manual documents Tandy's Memory PLUS expansion adapter: jumper E1-E2 for 128 KB, or E2-E3 with the extra 256 KB fitted.[11]
  • The HX has a free bay for a 3.5-inch hard disk but no power cable for it; the FAQ suggests wiring one from the main board power leads.[10]
  • The 8088 can be replaced by a NEC V20. There is no maths coprocessor socket.[12]

EEPROM and setup

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The HX keeps its settings in a serial EEPROM, changed with Tandy's setup program.[13][14]

  • To boot a later DOS from disk, set the primary start-up device to DISK. With the HX booting from ROM, CONFIG.SYS and AUTOEXEC.BAT on drive A: are ignored.[14]
  • Wikipedia reports that the MS-DOS 6 installer can corrupt the EEPROM, and that DOS 4.0 does not work on the HX.[13]
  • The FAQ warns that running a DeskMate program outside DeskMate can also corrupt the EEPROM on machines with DOS and DeskMate in ROM.[14]

BIOS

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The FAQ lists 02.00.00 as the only BIOS for the HX.[15]

Maintenance checklist

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  1. Check the rating label before connecting the mains.
  2. Unplug the machine and wait before opening the case.
  3. Remove dust from the supply, fan and drives; check that the fan turns freely.
  4. Inspect the supply board for bulging or leaking electrolytics.
  5. Clean the floppy heads and check the drive select jumpers.
  6. Run the machine and measure +5 V, +12 V and -12 V against the table above.
  7. Note the setup program's settings before changing DOS versions.
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References

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  1. ↑ 1.0 1.1 1.2 1.3 Tandy Corporation, Tandy 1000 EX Technical Reference Manual, catalogue no. 25-1510, 1986, hosted as File:Tandy 1000 EX Technical Reference Manual (25-1510, 1986).pdf. 28 W supply 8790083, PDF pp. 89-107.
  2. ↑ Blake Patterson, photograph of a Tandy 1000 HX power supply board (T1 marked TO-4349), 2019, CC BY 2.0.
  3. ↑ 3.0 3.1 Jeff Hayes, "Tandy 1000-series FAQ", version 2.52, 25 October 2005, TVDog's Tandy 1000 archive (retrieved 2026-10-21). Section II.E.1.
  4. ↑ Tandy 1000 EX Technical Reference Manual (25-1510), Main Logic Board connector pin assignments (J3 and J7 keyboard interface), PDF pp. 12-13; parts list (12-pin and 13-pin flat flex ZIF connectors), PDF p. 71.
  5. ↑ "Is the power supply fan in the 1000SX really needed?", Vintage Computer Federation forum, March 2019, thread. Post by blackepyon, 8 March 2019.
  6. ↑ Blake Patterson, photograph, 2019, CC BY 2.0: "Got the wrong fan-size advice, but I made do."
  7. ↑ 7.0 7.1 7.2 Hayes, "Tandy 1000-series FAQ" (2005), sections II.C.2 and II.C.5.
  8. ↑ Hayes, "Tandy 1000-series FAQ" (2005), section II.C.6.
  9. ↑ Hayes, "Tandy 1000-series FAQ" (2005), section II.C.4.
  10. ↑ 10.0 10.1 Hayes, "Tandy 1000-series FAQ" (2005), sections II.A.1, II.D.1 and II.I.1.
  11. ↑ Tandy 1000 EX Technical Reference Manual (25-1510), "Memory PLUS Expansion Adapter", PDF pp. 136-145.
  12. ↑ Hayes, "Tandy 1000-series FAQ" (2005), sections II.F.1 and II.F.2.
  13. ↑ 13.0 13.1 "Tandy 1000", Wikipedia (retrieved 2026-10-21). Section "1000 HX".
  14. ↑ 14.0 14.1 14.2 Hayes, "Tandy 1000-series FAQ" (2005), sections II.K.8, III.A.1, III.A.3 and III.F.1.
  15. ↑ Hayes, "Tandy 1000-series FAQ" (2005), section III.E.2, BIOS version table.


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