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TSU Meeting SUNDAY — February 16, 2025

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David Anderson, Carl Miles, Adam Trionfo, João (Museu Loja CX), Hugo, Gustavo, Johnny Red

Carl Miles led an in-depth design preview of his "TS1560" — a double-decker expansion for the TS1000/ZX81 that bundles 64K of switchable RAM (with 2K granularity in the lower 8K so the area can be ROM or RAM as needed), TS1510 cartridge support, a ROM-replacement cartridge, a fully programmable joystick interface using GAL/PAL chips, and an AY-3-8912 sound chip whose GPIO port drives an SD-card storage backend developed by a German collaborator. After discussion, the group convinced Carl to also fit a true RS-232 port modeled on the TS2050 modem's USART + clock circuitry, so existing 2050 terminal software (including Fred Nachbauer's 80-column terminal for the 1000) can be reused. ZX-Wespi was considered but ruled out because it requires opening the case, and FujiNet was discussed as an interesting parallel but out of scope for this design.

Carl also outlined two TS2068 experiments on Adam's machine. First, to track down the well-known 2068 audio hiss, he'll socket the 78S40 chip and splay out every regulator pin while leaving the on-die op-amp (which Timex repurposed for audio amplification) connected and powered — the theory being that switching-regulator noise bleeds across the die. Gustavo suggested an LM386 with bypass cap as a fallback. Second, Carl demoed a stereo-AY board (inspired by Spectrum 128/+2 designs) that replaces the composite RCA jack with a TRS jack carrying composite plus stereo AY audio, mutes the internal speaker when plugged in, and falls back to mono when unplugged — avoiding any new holes in the case. Jumpers select ABC vs. ACB channel mapping for Spectrum software written to either convention. Capacitor health on US-made 2068s came up too; the Sam Young-branded caps inside turn out to be a Korean subsidiary of Nippon Chemi-Con and have held up well, unlike the Jellic caps in UK Spectrums.

João (Museu Loja CX), Hugo, and Johnny Red joined from Portugal. João recapped the 2024 ZX Spectrum Game of the Year ceremony run with Planeta Sinclair — now hosted in English, broadcast live on YouTube with an international jury, the red carpet in Cantanhede, professional co-host, and reveal trailers for unreleased 2025 Spectrum games. The bigger announcement was the new mainstream documentary "Timex Portugal: An Untold Revolution," aired on RTP (Portuguese public TV) two weeks ago and now carrying English subtitles on the RTP player. The film tells the Timex Portugal factory story (watches, computers, IBM/Minolta/Ugine-Swida work) through interviews with former employees including marketing and production directors, framed around the impact of the 1974 Carnation Revolution. The group's role in the British "Rubber Key Wonder" Spectrum documentary was also discussed.

Hugo gave a status update on the TENET reproduction. The board has been shrunk to a smaller SMD footprint with the two original PAL components collapsed into a single modern SCLD chip (logic preserved bit-for-bit), while keeping DIP sockets for the EPROMs so owners can reprogram and improve the Z80 firmware — to be released under an LGPL-style license with Gerbers published. Hugo also recounted finding a fourth surviving TENET unit (donated by Paul Quay) that contained a newer Z8 ROM with bug fixes, prompting them to slow the release down to get the software right. He also shared a story of a 1980s Portuguese supermarket that ran point-of-sale over a TENET network, and Gustavo added Argentine examples — a Timex-based parking system and a pharmacy POS using FDD3 drives, chosen because operators preferred the large TS character set over the IBM PC. The next meeting is Monday, March 3rd.

Highlights

  • Carl Miles previewed his "TS1560" — a stacked TS1000/ZX81 expansion with 64K RAM, TS1510 cartridges, ROM replacement, programmable joystick, RS-232 (modeled on the TS2050), and an AY-3-8912 with SD-card storage.
  • Plan to socket the 2068's 78S40 chip and disable its switching-regulator section while keeping the on-die op-amp powered, to confirm it's the source of the 2068's audible hiss.
  • Carl demoed a stereo-AY board for the 2068 that reuses the composite-jack hole for a TRS jack carrying composite video plus stereo audio and mutes the internal speaker when plugged in.
  • João walked the group through "Timex Portugal: An Untold Revolution," newly aired on RTP and now subtitled in English on the broadcaster's player.
  • TENET reproduction status: SMD redesign with the two original PALs collapsed into one SCLD, EPROM sockets retained, Gerbers and lessons-learned to be released openly.

Projects discussed: "1068" — Enhanced TS1000 Topics: TS1000 / ZX81 / TS1500 · Hardware projects & new boards · TS2068 / TC2068 · Timex Computer (European: TC2048/3256) · Modems, serial & RS-232 · ZX Spectrum

Summary generated from the meeting recording; the full transcript is kept in the group's private archive.