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Tandy 102

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Tandy 102
Tandy 102 and Tandy 200 (mk97007)
A Tandy 102 in front of a Tandy 200 (photo: mk97007, CC BY 2.0)
Specifications
ManufacturerTandy Corporation (sold through Radio Shack)
TypePortable computer
Released1986
CPU80C85A (MSM80C85ARS), 2.4576 MHz
Memory24 KB CMOS static RAM, expandable to 32 KB
StorageCassette interface at 1,500 bit/s
Display240 x 64 dot LCD, 40 x 8 characters
SoundBuzzer
ROM32 KB masked ROM; socket for a 32 KB option ROM
PowerFour AA alkaline cells or AC adaptor 26-3804
Dimensions300 x 215 x 38.5 mm (11-3/4 x 8-1/2 x 1-1/2 in)
Weight1.4 kg (3 lb 2 oz) with batteries
OS / FirmwareBASIC, TEXT, TELCOM, ADDRSS and SCHEDL in ROM
PredecessorTRS-80 Model 100
Model no.26-3803

The Tandy 102 is a battery-powered portable computer that Tandy introduced in 1986 as a direct replacement for the TRS-80 Model 100. It runs the same software and has the same keyboard and screen, in a thinner case that weighs about a pound less; the reduction came from surface-mount parts.[1] Tandy's service manual calls it "a low cost version" of the Model 100, fully compatible with it in software, with BASIC, TEXT, TELCOM, ADDRSS and SCHEDL in ROM. Files are kept in battery-backed RAM, held up by a rechargeable cell on the main board when the AA cells are out.[2] The Tandy 200 is a separate, larger design with a flip-up screen.

Specifications

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Tandy 102 specifications (Service Manual, pp. 1-7 and 1-8)
Item Detail
CPU 80C85A (M19, MSM80C85ARS), code and pin compatible with the 8085; 4.9152 MHz crystal X2, 2.4576 MHz clock
ROM 32 KB standard (M12); 32 KB option ROM in socket M11, reached through a cover in the base
RAM 24 KB standard as three 8 KB CMOS static RAMs (M7 to M9); a fourth in socket M6 gives 32 KB
Display 240 x 64 dot LCD, 1/32 duty; eight lines of 40 characters
Keyboard 72 keys in an 8 x 9 matrix
Interfaces RS-232C (DB-25, 75 to 19,200 bit/s); Bell 103 modem at 300 bit/s with pulse dialling; Centronics printer; cassette at 1,500 bit/s; bar code reader; 40-pin system bus
Power Four AA alkaline-manganese cells, about five days at four hours a day; AC adaptor 26-3804; 65 mA typical consumption
Memory backup Rechargeable battery, 50 mAh, 3.6 V, trickle-charged at 1.2 mA typical; more than 20 days with 16 KB, more than 10 days with 32 KB

Sources: the specifications and connector descriptions,[2] the memory description,[3] and the parts list.[4]

Hardware

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Boards

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The case holds three boards: the main board, the LCD board and the keyboard.[2] The main board is marked PLX144FHIX on the service manual's drawing.[5] Stephen Adolph's list of Model 100 and 102 variants on the Bitchin100 wiki gives PLX144FH1X for the US 102, and different boards for the European (PPPCG2007A*01) and UK (PLX196CH1X) versions, both with their own ROMs.[6] Most of the logic is high-speed CMOS in flat packages (TC40H-series parts),[4][1] and the LCD board carries ten HD44102 segment drivers and two HD44103 common drivers with ceramic capacitors only.[4] All of the electrolytic capacitors are on the main board; see the Tandy 102 Capacitor Replacement Guide.

Power supply

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The logic runs on VDD (+5 V) and VEE (−5 V) from a DC/DC converter: transformer OT2, oscillated by T21 and T22, with VDD rectified by D13 and smoothed by C84 and VEE rectified by D15 and smoothed by C85. VDD is held at 5 V by feedback through zener diode D4 to T13. A third rail, VB, is +4 to +5 V and is kept up by the backup battery with the power switched off.[7][8] The low-battery LED lights when the supply falls to 4.2 V ±0.1 V, and the converter is stopped at 3.7 V, about 20 minutes later in use. The computer also switches itself off after ten minutes without use.[7] The schematic of this section is reproduced at File:Tandy 102 power supply and reset circuits (Service Manual Fig. 7-1).png.

Memory backup battery

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The memory backup cell is a Ni-Cad battery, part 3-51FT, Radio Shack part ACS-0100, the same part number as the Model 100's.[4][9] The MEMORY POWER switch on the base disconnects it; the 102 will not run with the switch off, and the RAM is not backed up.[2] Brian K. White lists the 3-V80/H nickel-metal hydride cell as his replacement for the original 3-51FT-A in the 102.[10]

Known faults

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  • A leaking backup battery damages the fine traces around it. Jeff Birt has seen a 102 where the leak had eaten the traces in that area and left a garbled screen from bus damage, and Geoffrey Oltmans found the long trace along the edge of the board that carries backup power to the RAM etched through.[11][12]
  • Owners on the Model 100 mailing list report that the 102's electrolytic capacitors leak less than the Model 100's; some recap the 102 as a precaution.[13][14]
  • Fugu ME100 describes the 102's board as prone to hairline cracks in its traces, and traced a 102 that would start only after the RESET button was pressed to a cracked trace to the reset capacitor.[15]

See the Tandy 102 Troubleshooting Guide for these and the manual's checking procedures.

Documentation

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References

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  1. ↑ 1.0 1.1 Wikipedia, "TRS-80 Model 100", section on the Tandy 102 (retrieved 2026-10-21). Introduced in 1986 as a direct replacement for the Model 100 with the same software, keyboard and screen; thinner and about one pound lighter through surface-mount packaging; 24K standard, upgradable to 32K with an ordinary 8K SRAM chip.
  2. ↑ 2.0 2.1 2.2 2.3 Tandy, Service Manual: Tandy 102 Portable Computer, catalogue number 26-3803, Part I, pp. 1-2 to 1-8: system overview (a low cost version of the Model 100, software compatible), external views, switches and connectors, the MEMORY POWER switch and Ni-Cad backup battery, and the specifications. Hosted as File:Tandy 102 Service Manual (26-3803).pdf, described at Tandy 102 Service Manual.
  3. ↑ Service Manual: Tandy 102, Part IV, "CPU" and "Memory", p. 4-3: the 80C85A at 2.4576 MHz; a 32 KB standard ROM, three 8 KB CMOS static RAMs in M9, M8 and M7, and M6 to make 32 KB; the option ROM in a socket under the ROM cover in the base.
  4. ↑ 4.0 4.1 4.2 4.3 Service Manual: Tandy 102, Part VI, electrical parts list, pp. 6-2 to 6-11: main board capacitors (p. 6-2), connectors, diodes and integrated circuits including the RAMs M7 to M9 (µPD4364C or TC5565PL-15), ROM M12 (HN613256PD-91) and CPU M19 (p. 6-3), crystals X1 to X3 (p. 6-7), the LCD board parts, all ceramic capacitors (p. 6-8), and the mechanical parts list with the Ni-Cad battery 3-51FT, RS part ACS-0100 (p. 6-11).
  5. ↑ Service Manual: Tandy 102, Fig. 1-4, "Main PCB (Bottom View)", p. 1-5, rendered as File:Tandy 102 main board (Service Manual Fig. 1-4).png.
  6. ↑ Stephen Adolph, "Model and ROM information", Bitchin100 DocGarden wiki, updated 1 May 2022 (retrieved 2026-10-21). Community source. Tandy 102 variants: USA 26-3803, PCB PLX144FH1X, ROM M53256-02 or 3256D91-5B1; EU and UK versions with different PCBs and ROMs; the 102 used a 27C256-compatible ROM pinout from the start.
  7. ↑ 7.0 7.1 Service Manual: Tandy 102, Part IV, "Power Supply Circuit", p. 4-24: the DC/DC converter (OT2, T21, T22, R126, C81), VEE from pin 9 via D15 and C85, VDD from pin 7 via D13 and C84, feedback through D4 to T13; the low-power detector (LED at 4.2 V ±0.1 V, shutdown at 3.7 V, about 20 minutes between them); automatic power-off after 10 minutes; the reset circuit with C78, R103, T9 to T11, TH2 and T25.
  8. ↑ Service Manual: Tandy 102, Part V, Troubleshooting, pp. 5-1 to 5-11: the troubleshooting guide and checking procedures for each function, including the converter checks (p. 5-3), clock (p. 5-6), memory protection (p. 5-7) and the check list (p. 5-11).
  9. ↑ Radio Shack, Service Manual: TRS-80 Model 100 Portable Computer, 26-3801/3802, Section VI, p. 6-11: memory battery P-36, "Battery Ni-Cad 3-51FT", RS part ACS-0100. Hosted as File:Radio Shack TRS-80 Model 100 Service Manual (26-3801, 26-3802).pdf.
  10. ↑ Brian K. White, "Re: NEC PC8201A Capacitor Kit", M100 mailing list, 16 October 2022 (retrieved 2026-10-21). Community source. Electrolytic capacitor lists from his own machines, including the Tandy 102 main board, and the memory battery: BAT1 3.6 V NiMH 2-pin (3-V80/H), original 3-51FT-A NiCd.
  11. ↑ Jeff Birt, "Re: Fwd: Error on laptop. Nicd or something serious?", M100 mailing list, 25 March 2022 (retrieved 2026-10-21). Community source. A leaking NiCad in the T102 tends to eat away the fine traces in that area, which can be impractical to repair; a garbled LCD is probably bus damage from the leak.
  12. ↑ Geoffrey Oltmans, "Re: Unresponsive Model 102", M100 mailing list, 28 December 2015 (retrieved 2026-10-21). Community source. On a Model 102 the old battery had leaked down the side of the board and etched through the long edge trace that powers the RAM when the computer is off; bridged with a short jumper.
  13. ↑ Josh Malone, "Re: Subtle differences among various Model T models", M100 mailing list, 3 January 2021 (retrieved 2026-10-21). Community source. The 102 does not seem to suffer the capacitor leakage of the Model 100.
  14. ↑ Joshua O'Keefe, "Re: caps", M100 mailing list, 12 October 2020 (retrieved 2026-10-21). Community source. A full precautionary recap of a working T102 that showed no capacitor failure; the M100 suffers more capacitor failures than the 102.
  15. ↑ Fugu ME100, "Re: M102 weird behavior and bodge wires", M100 mailing list, 25 September 2017 (retrieved 2026-10-21). Community source. Two factory bodge wires at the printer port, both grounds, on every T102 he had seen; T102 boards develop micro-cracks in traces; a cracked trace to the reset capacitor that left a 102 starting only after pressing RESET; dry joints at the clock IC.


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