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Tandy 102 Capacitor Replacement Guide

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Tandy 102 main board (Service Manual Fig. 1-4)
Tandy 102 main board from the service manual (Fig. 1-4), with the capacitor references. The converter capacitors C82 to C86 and C92 are at the bottom right, around OT2 and the clock chip M18

All of the Tandy 102's electrolytic capacitors are on the main board: 17 of them, listed with their values in Tandy's service manual. The LCD board uses only ceramic capacitors.[1] The positions and values are the same as on the TRS-80 Model 100's main board apart from the voltage rating of C83, and Brian K. White's list from his own 102 matches the manual.[2][3]

Which capacitors fail

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Owners on the Model 100 mailing list report that the 102's capacitors leak less than the Model 100's; the Model 100's failures are covered in the TRS-80 Model 100 Capacitor Replacement Guide.[4][5] Some owners recap a working 102 as a precaution, and Jeff Birt would usually recap a 102 he was working on for someone else.[5][6] If the supplies are wrong or the board shows any electrolyte, the converter group C82 to C86 is the first place to look; see the Tandy 102 Troubleshooting Guide. For what failed capacitors look like, see Capacitor Failure Symptoms.

Capacitor list

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Tandy 102 main board electrolytic capacitors
Ref Value (parts list) RS part number Circuit (schematic) Position on the board (Fig. 1-4)
C49 10 µF 16 V CC-106MDAP Supply decoupling for the modem op-amps Beside the upper TL064 (M29)
C50 10 µF 16 V CC-106MDAP Supply decoupling for the modem op-amps Beside the upper TL064 (M29)
C52 1 µF 50 V CC-105MJAP Modem filter; marked non-polarised (NP) on the schematic Beside the lower TL064 (M30)
C54 10 µF 16 V CC-106MDAP Supply decoupling for the modem op-amps Beside the lower TL064 (M30)
C55 10 µF 16 V CC-106MDAP Supply decoupling for the modem op-amps Beside the lower TL064 (M30)
C75 47 µF 16 V CC-476MDAP
C76 47 µF 16 V CC-476MDAP
C77 47 µF 16 V CC-476MDAP
C78 3.3 µF 50 V CC-335XJAP Reset delay, with R103 Bottom left corner, by the adaptor jack
C82 4.7 µF 25 V CC-475MFAP Converter supply Beside the converter transformer OT2
C83 470 µF 16 V CC-477RCAP Converter input, after the power switch SW5 Beside OT2
C84 470 µF 6.3 V CC-477BBAP VDD (+5 V) output Right of OT2, beside the clock chip M18
C85 33 µF 10 V CC-336MCAP VEE (−5 V) output, after D15 Beside the VDD test point
C86 100 µF 6.3 V CC-107MBAP VEE output, after R97 Right of OT2, beside M18
C90 1 µF 50 V CC-105MJAP VB backup rail Beside the VB test point
C92 0.47 µF 50 V CC-474MJAP VDD feedback, with R121 at T13 Right of OT2, beside M18
C103 220 µF 10 V CC-227MCAP Modem section, beside R32 Beside the modem transformer OT1

Sources: values and part numbers from the parts list;[1] circuit positions from the main board schematic;[7][8] board positions from the main board drawing.[9] C75 to C77 are not labelled on the board drawing, so find them by their 47 µF 16 V markings.

Where the manual disagrees with itself

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  • C92 is printed in the parts list as 0.047 µF 50 V, but both its part numbers (CC-474MJAP and CEVGR47ALX) are 0.47 µF codes, and the schematic marks it 0.47 µF. The Model 100's list gives 0.47 µF 50 V for the same position.[1][7][2] Fit 0.47 µF.
  • C103 is printed as "221 µF/10V"; its part number CC-227MCAP is 220 µF, and the schematic marks it 220 µF 16 V.[1][7]
  • The schematic marks C82 and C83 as 10 V parts, where the parts list gives 25 V and 16 V.[7][1]
  • The schematic shows a 1 µF electrolytic, C101, across VDD; the parts list gives C101 as "not used".[7][1] Check your own board.

Where the two figures differ, fit the higher voltage rating: 25 V for C82 and 16 V for C83 and C103.

Procedure

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  1. Copy off any files you want to keep, then take out the AA cells and disconnect the adaptor.
  2. Open the case and lift out the main board as described in General Maintenance: four screws A, the keyboard and LCD flat cables, the insulator board, then the two screws B.[10] Take care with the keyboard flat cable, whose contacts lift easily.
  3. Note the polarity of each capacitor before removing it.
  4. Remove the capacitors. Birt's method on the Model 100, whose pads into the ground and supply planes have no thermal relief and defeat a desoldering tool, is to heat one leg and push the top of the capacitor the other way, then do the same on the other leg, walking it out over three or four goes. He scrapes off corroded solder first, because the oxides melt at a much higher temperature, and preheats a difficult board to about 100 °C with a small heat gun.[11]
  5. Inspect the pads and traces under each capacitor, and the traces around the memory backup battery. Clean any residue as described in Battery Explosion, Capacitor or Corrosion Damage.
  6. Fit the new capacitors, observing polarity on all but C52. Keep them no taller than the originals; the 102's case is thinner than the Model 100's.[12]
  7. Look at the Ni-Cad memory battery while the board is out and replace it if it shows any sign of leaking; see General Maintenance.
  8. Refit the board and close the case.

Kits sold for the "Model 100/102" by Console5 and Arcade Shopper are mentioned on the Model 100 mailing list.[13] Check a kit against the table: on the 102, C83 should be rated at least 16 V.

Checks after recapping

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Supply checks (Service Manual, pp. 5-3 and 5-7)
Point Expected
Converter transformer OT2, pin 1 3.6 to 8 V
VDD +5 V
VEE −5 V
VB, power on +5 V
VB, power off 2.0 to 4.0 V

Source: the checking procedures.[14] Then run Tandy's check list, given on the General Maintenance page.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Tandy, Service Manual: Tandy 102 Portable Computer, catalogue number 26-3803, Part VI, electrical parts list: main board capacitors C1 to C111 with type, value, voltage, tolerance and Radio Shack and manufacturer part numbers (p. 6-2 and the top of p. 6-3); LCD board capacitors C1 to C20, all ceramic (p. 6-8). Hosted as File:Tandy 102 Service Manual (26-3803).pdf, described at Tandy 102 Service Manual.
  2. ↑ 2.0 2.1 Radio Shack, Service Manual: TRS-80 Model 100 Portable Computer, 26-3801/3802, Section VI, parts list, pp. 6-3 and 6-4: the same 17 electrolytic positions, with C83 470 µF 10 V. Hosted as File:Radio Shack TRS-80 Model 100 Service Manual (26-3801, 26-3802).pdf.
  3. ↑ Brian K. White, "Re: NEC PC8201A Capacitor Kit", M100 mailing list, 16 October 2022 (retrieved 2026-10-21). Community source. His capacitor notes from his own machines, including the Tandy 102 main board (C49, C50, C52, C54, C55, C75 to C78, C82 to C86, C90, C92, C103) and the memory battery replacement 3-V80/H.
  4. ↑ 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.
  5. ↑ 5.0 5.1 Joshua O'Keefe, "Re: caps", M100 mailing list, 12 October 2020 (retrieved 2026-10-21). Community source. A full recap of a working T102 that showed no sign of capacitor failure, as preventive maintenance; the M100 suffers more capacitor failures than the 102.
  6. ↑ Jeffrey Birt, "Re: Preemptive recapping", M100 mailing list, 19 August 2020 (retrieved 2026-10-21). Community source. Would more than likely recap a Model 100 or 102 being done for someone else, since the parts are cheap and the M100 is known for leaking capacitors; many people make things worse by recapping without the right tools or experience.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 Service Manual: Tandy 102, Fig. 7-1, "Main PCB - Schematic Diagram", p. 7-1: the power section (C78, C82 to C86, C90, C92, C101), the modem filter and op-amp supply decoupling (C47 to C50 and C54 to C57, "0.1 µ x 4, 10 µ 16 V x 4"; C52 1 µ 50 V NP) and C103 220 µ 16 V. Power section rendered as File:Tandy 102 power supply and reset circuits (Service Manual Fig. 7-1).png.
  8. ↑ Service Manual: Tandy 102, Part IV, "Power Supply Circuit", p. 4-24: VEE filtered by C85 and VDD by C84; C78 and R103 delay the reset; Part V, p. 5-3: with less than 3.6 to 8 V at pin 1 of the converter transformer, check C82 and C83.
  9. ↑ 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.
  10. ↑ Service Manual: Tandy 102, Part II, pp. 2-1 and 2-2: case screws A, the flat cables to the keyboard and LCD boards, the insulator board and the two screws B holding the main board.
  11. ↑ Jeffrey Birt, "Re: Recap and new battery", M100 mailing list, 16 February 2023 (retrieved 2026-10-21). Community source. No thermal reliefs on pads into the ground and supply pours; walking capacitors out leg by leg; scraping off corroded solder; preheating the board to about 100 °C.
  12. ↑ Wikipedia, "TRS-80 Model 100", section on the Tandy 102 (retrieved 2026-10-21). The 102 is thinner than the Model 100.
  13. ↑ Gregory McGill, "Re: Types of caps in M100", M100 mailing list, 12 July 2019, and Jason Jorgenson, "Re: is there a Model 100 Capacitor kit available (2024)", 17 March 2024 (both retrieved 2026-10-21). Community sources. Model 100/102 capacitor kits from Arcade Shopper and Console5.
  14. ↑ Service Manual: Tandy 102, Part V, pp. 5-3, 5-7 and 5-11: converter and supply checks, memory protection checks, and the check list.


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