Tandy 1400 LT
.jpg) | |
| A Tandy 1400 LT with its LCD raised and the two 3.5-inch drives on the front (photo: DigitalIceAge, CC BY 4.0) | |
| Specifications | |
|---|---|
| Manufacturer | Tandy Corporation, sold by Radio Shack |
| Type | Laptop computer (IBM PC compatible) |
| Released | November 1987 |
| Discontinued | 1991 |
| Intro price | US$1,599 |
| CPU | NEC V20, 7.16 MHz or 4.77 MHz |
| Memory | 768 KB (640 KB for MS-DOS, 128 KB for a RAM disk or print spooler) |
| Storage | Two 720 KB 3.5-inch floppy drives |
| Display | Backlit supertwist LCD, 640 x 200, 80 x 25 text |
| Sound | — |
| Power | 12 V 2200 mAh NiCd battery pack; 15 V DC 700 mA AC adapter |
| Dimensions | 3.5 x 14.5 x 12.375 in |
| Weight | 13.5 lb |
| OS / Firmware | MS-DOS 3.2 with GW-BASIC |
| Successor | Tandy 1400 FD, Tandy 1400 HD |
| Model no. | 25-3500 |
The Tandy 1400 LT (catalogue number 25-3500) was Tandy's first MS-DOS laptop. Radio Shack introduced it in November 1987 at US$1,599.[1] It has an NEC V20 processor, 768 KB of RAM, two 720 KB 3.5-inch floppy drives and a backlit supertwist LCD, and runs from a removable 12 V nickel-cadmium battery pack.[2]
History
[edit | edit source]A review by Renato Reyes, sysop of the Tandy Professional Forum, gave the price as $1,599, extra battery packs as $79.95, and the expected arrival in Radio Shack stores as November.[3] Wikipedia records that Tandy later sold an external 5.25-inch drive for it, that the revised 1400 FD and 1400 HD followed, and that the 1400 family was dropped from Radio Shack catalogues after 1991.[1] An owner noted in 1988 that machines are marked 3500 or 3500A on the identification plate underneath, the A indicating a minor change to the power supply.[4]
Specifications
[edit | edit source]| Item | Detail |
|---|---|
| Processor | NEC V20 (uPD70108), 7.16 or 4.77 MHz, switchable |
| Memory | 16 KB ROM; 768 KB RAM in 256K x 4 DRAMs, 640 KB for MS-DOS and 128 KB for a RAM disk or print spooler |
| Display | Backlit supertwist LCD, 640 x 200 pixels, 80 x 25 characters, aspect ratio 1:1.4; outputs for an RGBI colour monitor and composite video |
| Drives | Two internal 720 KB 3.5-inch double-sided drives; port for an external drive |
| Keyboard | 76 keys; port for an external 101-key keyboard |
| Ports | DB-25 parallel, DB-9 serial, RGBI, composite video, external drive, external keyboard |
| Modem | Optional internal 1200 bps Hayes-compatible modem |
| Clock | Ricoh RP5C15 real-time clock with its own backup battery |
| Power | Removable 12 V 2200 mAh battery, about 4 hours; AC adapter 15 V DC 700 mA |
| Size and weight | 3.5 x 14.5 x 12.375 in; 13.5 lb |
Sources: the service manual's specification and hardware pages.[2][5]
Hardware
[edit | edit source]The service manual describes eight printed circuit boards, including the main PCB, the power source PCB with a sub PCB, a memory PCB, the LED PCB and the LCD unit.[6] A DIP switch, DS1, enables or disables the memory blocks at 40000H-9FFFFH and DC000H-FBFFFH, and a boot select switch, SW3, decides whether drive A: is the first internal drive or an external 5.25-inch drive.[5] The floppy drives use a brushless direct-drive motor turning the spindle at 300 rpm.[7]
The power supply is an integrated regulator of about 13 W. A switching regulator built around a uPC494 controller and transistor TR511 gives +5 V at up to 2.5 A, with a thyristor (SCR500) to protect the load if TR511 fails short. A ringing choke converter with transistor TR508 and transformer T500 gives +12 V, -12 V and the -15 V LCD bias, and a separate inverter (TR512, T501) drives the electroluminescent backlight.[8]
The main battery is a 12 V 2200 mAh nickel-cadmium pack. A separate 3.6 V nickel-cadmium cell on the main PCB keeps the real-time clock running. The machine warns of a low battery at 11.7-11.9 V and tells the user to shut down at 10.8-11.4 V; after that it shuts itself down and the contents of RAM are lost.[9]
Known faults
[edit | edit source]- Hard disk kits for the 1400 LT drew more current than the original adapter could supply. One installer wrote that with a hard disk spinning the machine draws about 1 A, more than Tandy's 750 mA adapter can supply while also charging the battery.[10]
- Owners who fitted a hard disk had to short resistor R554 on the power supply board, and then found that running from the adapter discharged the battery. Their fix moves a 27-ohm resistor, with a Schottky diode across it, into the battery lead from the disk controller.[4][10] The parts list gives R554 as a 27-ohm 2 W resistor.[11]
- An owner reports that his 1400 will not start from the adapter until the battery has taken some charge.[12]
Fault-finding is on Tandy 1400 LT Troubleshooting Guide.
Documentation
[edit | edit source]- Tandy 1400 LT Service Manual (25-3500, 1988): disassembly, preventive maintenance, theory of operation, troubleshooting flowcharts, parts lists, circuit diagrams and PCB views, with appendices on the LCD, EL backlight replacement and the floppy drive. File:Tandy 1400 LT Service Manual (25-3500, 1988).pdf
Related pages
[edit | edit source]- Tandy 1400 LT General Maintenance
- Tandy 1400 LT Troubleshooting Guide
- Tandy 1400 LT Capacitor Replacement Guide
- Tandy 1100 FD
- Floppy Drive Repair
References
[edit | edit source]- ↑ 1.0 1.1 "Tandy 1400 LT", Wikipedia (retrieved 2026-10-22).
- ↑ 2.0 2.1 Tandy Corporation, Tandy 1400LT Laptop Computer Service Manual, catalogue no. 25-3500, 1988, hosted as File:Tandy 1400 LT Service Manual (25-3500, 1988).pdf. Specifications page.
- ↑ Renato Reyes, "Tandy's new laptop is a winner", review for the Tandy Professional Forum, 1987, TVDog's Tandy 1000 archive (retrieved 2026-10-22).
- ↑ 4.0 4.1 Stephen Lankton, CompuServe messages "1400LT Hard Disk", 5 October and 8 November 1988, cmshd.txt, TVDog's Tandy 1000 archive (retrieved 2026-10-22).
- ↑ 5.0 5.1 Tandy 1400LT Service Manual, Part I, "Hardware Specifications", pp. 1-7 to 1-9.
- ↑ Tandy 1400LT Service Manual, Part I, "Internal View", pp. 1-4 to 1-6; Part VI, parts lists.
- ↑ Tandy 1400LT Service Manual, Appendix C, "3.5 inch FDD Specifications".
- ↑ Tandy 1400LT Service Manual, Part IV-20, "Power Supply", pp. 4-55 to 4-58.
- ↑ Tandy 1400LT Service Manual, Part IV-20, "Power Source", p. 4-56; Main PCB parts list (BATT1), p. 6-9.
- ↑ 10.0 10.1 Rusty Hill and others, CompuServe messages on the 1400LT, 1400ltdk.txt, TVDog's Tandy 1000 archive (retrieved 2026-10-22).
- ↑ Tandy 1400LT Service Manual, Part VI-2, Power PCB Assembly parts list, pp. 6-16 to 6-18.
- ↑ "Can someone tell me why my TANDY 1110HD computer will not power on?", Vintage Computer Federation forum, thread. Post by mojorific, 16 May 2014.