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Tandy 102 General Maintenance

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Tandy 102 main board (Service Manual Fig. 1-4)
Tandy 102 main board from the service manual (Fig. 1-4). The memory backup battery (3-1FT) is on the left; the power section is at the bottom right, around the converter transformer OT2

The Tandy 102 has no mains voltage inside. It runs from four AA cells or a low-voltage adaptor through a DC/DC converter on the main board, and everything the owner has stored is in static RAM held up by a Ni-Cad cell when the computer is off.[1][2] The maintenance jobs owners report on the 102 are the backup cell, which can leak onto the board, and the keyboard's flat cable, which is easily damaged when the case is opened.[3][4]

Before you start

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  • Copy any files you want to keep to another computer through the RS-232C port, or to cassette. They exist only in RAM.[2]
  • Switching MEMORY POWER off, or removing the backup battery, loses the RAM contents. The 102 will not run with MEMORY POWER off.[2]
  • Disconnect the adaptor and any cables, and take out the AA cells.[5]

Opening the case

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  1. Turn the computer over on a soft surface so the screen and key tops are not scratched, and remove the four screws A that hold the upper and lower cases together.[5]
  2. Lift off the upper case. Snaps hold the halves together; Tandy's instruction is to pull up the front of the upper case first and not to use too much force.[5] Club 100's notes, kept on the Bitchin100 wiki, say the 102 splits the same way as the Model 100: stand it on its right-hand edge, press in on the middle of the top and front edges of the bottom half, and pull the top half away.[6]
  3. Disconnect the flat cable from the connector on the keyboard board and lift out the keyboard, then disconnect the flat cable from the LCD board and lift out the LCD board.[5] The keyboard cable has 18 lines and the LCD cable 30.[7]
  4. To take out the main board, remove the insulator board and the two screws B.[5]

The keyboard flat cable

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The ends of the 102's keyboard cable are copper tracks on a thin plastic stiffener, and they push into edge connectors. Several owners have had the tracks lift or fold back while refitting the cable.[4][8] Push the cable into its connector in one straight movement; each extra attempt disturbs the tracks.[9] Brian White has repaired a damaged end by flattening the tracks, cleaning the cable and stiffener with isopropyl alcohol, and sticking the tracks back down on the stiffener with permanent double-sided tape.[9]

Replacement cables reported to work are 18-way flexible flat cable at 1.25 mm pitch, with the exposed contacts on opposite sides at the two ends; the original is 150 mm long. David Plass fitted a 229 mm Molex 15168-0250 and needed a playing card as a shim to make it grip.[10][8] Jeff Birt has seen damaged connectors alongside damaged cables, so look at the connectors as well.[11]

Cleaning

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Tandy's manual calls for a soft, dry, lint-free cloth on the case and LCD, and benzol for stubborn marks, with no other solvent.[12]

For a key that has stopped working, Fugu ME100's method on the Model 100 is to ease open the two plastic tabs that lock the key cap to its base, take out the spring and metal disc, and clean inside with a cotton bud and contact cleaner; it takes no force once the tabs are open.[13] Each key on the 102 keyboard has its own diode; Josh Malone suggests checking the diode under a dead key with a meter on diode test, from the back of the keyboard board.[14]

Memory backup battery

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The backup cell is a Ni-Cad battery, part 3-51FT, Radio Shack part ACS-0100, rated 50 mAh at 3.6 V and trickle-charged at about 1.2 mA from the adaptor or the AA cells.[7][2] It sits on the left-hand side of the main board on the service manual's drawing, marked 3-1FT.[15]

  • Check it: with the computer switched off, VB should read 2.0 to 4.0 V. If it does not, the manual's checks are the Ni-Cad, D11 and D22.[16]
  • Look at it whenever the case is open. A leaking cell damages the fine traces around it, and on one 102 it etched through the long trace along the board edge that carries backup power to the RAM.[3][17] Treat any residue as described in Battery Explosion, Capacitor or Corrosion Damage.
  • Brian K. White uses a 3-V80/H nickel-metal hydride cell as the replacement.[18] George Rimakis worked out that the manual's 1.2 mA trickle current is about 0.015C for an 80 mAh cell, below the C/40 maintenance rate Energizer recommends for NiMH.[19]
  • Kurt McCullum fitted a supercapacitor in place of the battery in his 102 and found it held the memory for more than three days.[20] Jeff Birt points out that supercapacitors discharge themselves much faster than a battery, and after trying one he does not recommend it. He also advises desoldering the old battery, having seen boards damaged by people cutting batteries out.[21][22]
  • A 102 that has been stored for a long time may need a long charge before it behaves. Roma, whose group has owned more than a hundred 102s, leaves them on the adaptor with fresh AA cells fitted for 24 hours, and notes that rechargeable AA cells are not charged in the 102 without modification.[23]
  • For long storage the manual says to switch MEMORY POWER off, accepting that the RAM is then not backed up.[2]

Voltage checks

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Supply checks (Service Manual, pp. 5-3 and 5-7)
Rail or point Expected Parts to check if wrong
Converter transformer OT2, pin 1 3.6 to 8 V C82, C83, battery contacts, adaptor jack
VDD +5 V D13, C84, ZD1
VEE −5 V D15, C85, ZD2
VB, power on +5 V T27, T28, converter
VB, power off 2.0 to 4.0 V Ni-Cad battery, D11, D22

ZD1 and ZD2 are the board markings beside D13 and D15 on the service manual's drawing.[15] The low-battery LED lights at 4.2 V ±0.1 V from the AA cells or adaptor, and the converter is stopped at 3.7 V.[1] The adaptor is Radio Shack's AC Power Supply 26-3804.[2] Bob Pigford, citing Club 100's notes, warns that the adaptor is centre negative, unlike most low-voltage adaptors.[24]

Electrolytic capacitors

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The main board has 17 aluminium electrolytic capacitors; the LCD board has only ceramics.[25] Owners on the Model 100 mailing list report less leakage from the 102's capacitors than from the Model 100's, but Birt would usually recap a 102 he was working on for someone else, and advises looking at the capacitors whenever the case is open.[26][27][21] Values and the procedure are on the Tandy 102 Capacitor Replacement Guide.

Adjustments

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The LCD contrast is set with the display adjustment dial.[2] The one service adjustment in the manual is the modem transmit level:[28]

  1. Set the DIR/ACP switch to DIR.
  2. Connect a 600 ohm dummy load between pin 3 (RXMD) and pin 7 (TXMD) of the modem connector CN4, with an AC voltmeter across the load.
  3. In BASIC, enter OUT 178,47 and then OUT 168,02 to start the carrier.
  4. Adjust VR2 for −14 to −17 dBm, in both ANS and ORIG modes.

VR2 is the modem control in the parts list; the callout on the manual's board drawing calls it VR1, which is the contrast control.[29][15]

Optional RAM and ROM

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Both options fit without opening the case. Remove the RAM and ROM cover on the base with a coin, fit the optional RAM in the socket marked M6 and an option ROM in the socket marked M11.[30] The fitted RAMs are 8 KB CMOS static RAMs, µPD4364C or TC5565PL-15.[31]

Check list after any repair

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Tandy's check list starts with a cold start: hold CTRL and PAUSE and press the RESET switch on the back. All user files are erased. A warm start, pressing RESET or switching off and on, should leave the files in place.[16] Then:[16]

  1. In BASIC, run the display test:


10 FOR I=0 TO 255
20 PRINT CHR$(I);
30 NEXT I


40 ENDThe computer beeps once, clears the screen and prints every character.

  1. Set the date with DATE$="MM/DD/YY", the day with DAY$ and the time with TIME$="HH:MM:SS", return to the menu with MENU and check the calendar shows the new settings.
    2. 

  2. Check every key against the character code table.
    3. 

  3. Print the screen to a printer with the PRINT key.
    4. 

  4. Save a short program with CSAVE and read it back with CLOAD.
    5. 

  5. Test the RS-232C port and the modem between two computers.


The manual adds that the Model 100 diagnostics tape from Radio Shack can also be used.[16]



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References
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  1. ↑ 1.0 1.1 Tandy, Service Manual: Tandy 102 Portable Computer, catalogue number 26-3803, Part IV, "Power Supply Circuit", p. 4-24: the DC/DC converter making VDD (+5 V), VEE (−5 V) and VB (+4 to +5 V), the low-power detector and automatic power-off, and the reset circuit. Hosted as File:Tandy 102 Service Manual (26-3803).pdf, described at Tandy 102 Service Manual.

    2. 

  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 Service Manual: Tandy 102, Part I, pp. 1-2 to 1-8: switches and connectors, the MEMORY POWER switch and Ni-Cad backup battery, and the specifications, including the backup battery (50 mAh, 3.6 V, trickle charge at 1.2 mA typical; more than 20 days with 16 KB and more than 10 days with 32 KB).

    3. 

  3. ↑ 3.0 3.1 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 around it.

    4. 

  4. ↑ 4.0 4.1 Bert Put, "M-102 keyboard flat ribbon cable", M100 mailing list, 29 July 2020 (retrieved 2026-10-21). Community source. After opening a 102 to check the battery, the keyboard ribbon cable would not go back into its edge connector and some of its metal tracks had moved; the Model 100's keyboard connectors are much sturdier.

    5. 

  5. ↑ 5.0 5.1 5.2 5.3 5.4 Service Manual: Tandy 102, Part II, Disassembly instructions, pp. 2-1 and 2-2: disconnecting the cables, the four screws A, the snaps holding the case halves, the flat cables to the keyboard and LCD boards, the insulator board and the two screws B holding the main board.

    6. 

  6. ↑ "Splitting the Model 100/102/200 case", Bitchin100 DocGarden wiki, from the Club 100 support files (retrieved 2026-10-21). Community source. The 102 splits the same way as the Model 100; where to press to release the plastic notches; not pinching the keyboard wires on reassembly.

    7. 

  7. ↑ 7.0 7.1 Service Manual: Tandy 102, Part VI, Mechanical and assembly parts list, p. 6-11: flat cable for the keyboard, 18 lines (AW-0006); flat cable for the LCD, 30 lines (AW-0007); Ni-Cad battery 3-51FT (ACS-0100); IC sockets; the case parts and screws.

    8. 

  8. ↑ 8.0 8.1 David Plass, "Model 102 keyboard cable sourced!", M100 mailing list, 2 April 2023 (retrieved 2026-10-21). Community source. Molex 15168-0250, 18-pin 1.25 mm pitch opposite-side FFC, 229 mm against the stock 150 mm; loose in both connectors until shimmed with a playing card.

    9. 

  9. ↑ 9.0 9.1 Brian White, "Re: M-102 keyboard flat ribbon cable", M100 mailing list, 30 July 2020 (retrieved 2026-10-21). Community source. Repairing the end of a 102 keyboard cable with double-sided tape; inserting it in one smooth push to avoid repeated attempts.

    10. 

  10. ↑ kjohnson3, "Re: M-102 keyboard flat ribbon cable", M100 mailing list, 30 July 2020 (retrieved 2026-10-21). Community source. Replacement 102 keyboard cable: FFC, 1.25 mm pitch, 18 pins, type B (contacts on opposite sides), 150 mm.

    11. 

  11. ↑ Jeff Birt, "Re: Model 102 keyboard cable sourced!", M100 mailing list, 3 April 2023 (retrieved 2026-10-21). Community source. The 150 mm Molex cable has a 1,000-piece minimum order; damaged connectors are seen with damaged cables.

    12. 

  12. ↑ Service Manual: Tandy 102, Part III, Maintenance, p. 3-1: keep the 102 clean; a soft, dry, lint-free cloth for the body and LCD; benzol for tough stains; no other solvents.

    13. 

  13. ↑ Fugu ME100, "Re: Need a M102 keyswitch", M100 mailing list, 24 January 2018 (retrieved 2026-10-21). Community source. Opening a Model 100 key switch by easing the two plastic locking tabs, removing the spring and metal disc and cleaning with contact cleaner; assumes the 102's keys are similar.

    14. 

  14. ↑ Josh Malone, "Re: 102 Keyboard repair help RQ", M100 mailing list, 17 September 2022 (retrieved 2026-10-21). Community source. Each key on the 102 keyboard matrix has a diode; the switch pads and the diode pads are on the back of the keyboard board; check the diode reads about 0.6 V one way and open the other.

    15. 

  15. ↑ 15.0 15.1 15.2 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.

    16. 

  16. ↑ 16.0 16.1 16.2 16.3 Service Manual: Tandy 102, Part V, Troubleshooting: checking procedures for "Doesn't work at all" (p. 5-3), clock (p. 5-6), memory protection (p. 5-7), and the check list (p. 5-11).

    17. 

  17. ↑ Geoffrey Oltmans, "Re: Unresponsive Model 102", M100 mailing list, 28 December 2015 (retrieved 2026-10-21). Community source. Battery leakage had etched through the long edge trace that supplies backup power to the RAM; bridged with a jumper.

    18. 

  18. ↑ Brian K. White, "Re: NEC PC8201A Capacitor Kit", M100 mailing list, 16 October 2022 (retrieved 2026-10-21). Community source. Tandy 102 main board capacitor list and memory battery: 3.6 V NiMH 2-pin 3-V80/H, original 3-51FT-A NiCd.

    19. 

  19. ↑ George Rimakis, "Re: Oh no - think my internal nicad finally given up the ghost", M100 mailing list, 31 May 2017 (retrieved 2026-10-21). Community source. The Tandy 102 service manual's 1.2 mA trickle charge is about 0.015C on an 80 mAh cell; Energizer recommends a maintenance charge below C/40 for NiMH.

    20. 

  20. ↑ Kurt McCullum, "T200 Super Capacitor Warning", M100 mailing list, 15 April 2015 (retrieved 2026-10-21). Community source. A supercapacitor in place of the 102's internal battery worked, holding memory for more than three days; the same change caused problems in his Tandy 200.

    21. 

  21. ↑ 21.0 21.1 Jeffrey Birt, "Re: M-102 keyboard flat ribbon cable", M100 mailing list, 30 July 2020 (retrieved 2026-10-21). Community source. His video replaced the battery with a supercapacitor, which he does not recommend; desolder rather than snip the battery out; look at the electrolytic capacitors while the case is open.

    22. 

  22. ↑ Jeffrey Birt, "Re: New User - Resurrected T102", M100 mailing list, 25 July 2018 (retrieved 2026-10-21). Community source. Supercapacitors have a high self-discharge rate.

    23. 

  23. ↑ Roma, "Re: 102 Keyboard", M100 mailing list, 4 February 2017 (retrieved 2026-10-21). Community source. A 24-hour charge on the wall adaptor with four fresh AA cells revives the internal battery of a 102 that has not been used for a long time; rechargeable AA cells are not charged in the 102 without a modification.

    24. 

  24. ↑ Bob Pigford, "Re: 102 Keyboard", M100 mailing list, 4 February 2017 (retrieved 2026-10-21). Community source. The T102 owner's manual's cold start; Club 100's note on the adaptor: centre negative, and people adapt other nominal 6 V DC adaptors by fitting the right plug with that polarity.

    25. 

  25. ↑ Service Manual: Tandy 102, Part VI, electrical parts list: main board capacitors (p. 6-2), LCD board capacitors C1 to C20, all ceramic (p. 6-8).

    26. 

  26. ↑ 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.

    27. 

  27. ↑ Jeffrey Birt, "Re: Preemptive recapping", M100 mailing list, 19 August 2020 (retrieved 2026-10-21). Community source. Does not recap vintage equipment as a matter of course, but would recap a Model 100 or 102 being done for someone else, since the parts are cheap and the Model 100 is known for leaking capacitors.

    28. 

  28. ↑ Service Manual: Tandy 102, Part IV, "Modem Transmitting Level Adjustment", p. 4-19.

    29. 

  29. ↑ Service Manual: Tandy 102, Part VI, parts list, p. 6-7: VR1, 50k B-curve, contrast; VR2, semi-fixed 50k B-curve, modem.

    30. 

  30. ↑ Service Manual: Tandy 102, Appendix A, "Installation of Optional RAM and ROM", p. A-1.

    31. 

  31. ↑ Service Manual: Tandy 102, Part VI, parts list, p. 6-3: M7 to M9, C-MOS RAM µPD4364C or TC5565PL-15.

    32. 


















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