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TSU Meeting SUNDAY — September 17, 2023

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David, Joe, Paul Anderson, Jeff Burrell, Ryan Gray, Adam Trionfo, Tim Swenson, Brian

The group opened with project updates on a 3D-printed TS2068 cartridge case. Joe has been reworking an STL file Claudius supplied for the taller Portuguese-style cartridge so it fits the lower-profile American 2068 cartridge, taking advantage of surface-mount parts to drop the lid height. Alongside the case, David showed a redesigned cartridge PCB sized to fit inside that case: a 128K flash (8 × 16K images) selected by a small rotary switch, plus a low-profile write-protect switch so the cartridge can be programmed from the 2068 itself without being clobbered by a crash. Files will go on GitHub as an open project. Tom Bent / Tom Woods' old RAM/EEPROM cartridge (with Jeff Burrell's BASIC-to-ROM program) was cited as the precedent for in-machine cartridge programming.

David then walked through a candidate fix for the 2068's failing lower-RAM problem (toasted 4416 DRAMs after thermal stress, e.g. Randy Kindig's recently-overheated machine). Rather than chasing scarce 4416s, he laid out a small daughterboard derived from a Spectrum design that uses a 74-series latch to convert the RAS/CAS row/column scheme into a flat 14-bit address into a single static RAM. Some socket-extender height may be needed to clear the neighbouring chips.

The bulk of the meeting was a wide-ranging brainstorm on what a hypothetical successor to the TS2068 should be. Two camps emerged: a preservation-grade machine (a faithful 2068 with SD-card storage, modern video out, and the rear expansion bus retained for experimenter cards, possibly housed in the original case) versus a more ambitious evolution with extra video modes, more RAM, Ethernet, and Spectrum-compatible booting. Constraints were discussed candidly — Z80 bandwidth limits for large/colourful screens, the 50/60 Hz interrupt gap that breaks much Spectrum software on the 2068, and the lack of any 2068 demo scene to write new software. The Spectrum Next was reviewed (unobtainable, expensive, and its bank-switching doesn't match the 2068) along with the N-GO Spectrum Next-compatible board (~145 euros) as a form-factor reference. Tim Swenson reported that Derek Stuart — designer of the Q68 small-form QL clone — has offered to redo a 2068 PCB if someone sends him a dead board, and Jeff Burrell's prior FPGA 2068 work was flagged as the natural starting point. David also showed his custom Cherry-MX keyboard drop-in for the 2068 case.

Shorter items rounded out the meeting. Joe reported that the ZX-BesTie internet/video board for the ZX81/TS1000 only works in PAL/50 Hz mode — lifting R30 to force PAL fixed his long-standing failure to get it running. Paul Anderson confirmed that in the 1980s most dead 2068s the group repaired were power-supply related, and Carl Miles' tiny switching-regulator module (replacing the original linear 12 V regulator and the on-board 5 V switcher) was noted as a cleaner-video win, at the cost of the internal speaker op-amp. Tim opened a discussion on downsizing collections — what to keep, where to send hardware (TJ in California, VCF auctions) — and offered to demo a Cambridge Z88 at a future meeting. David noted that Willie is replicating the JLO disk system and they're investigating whether a Gotek floppy emulator can be paired with it; an inventory of newly-digitised newsletters and docs uploaded to archive.org will go out by email shortly. Next meeting: Monday October 2, 9 PM Eastern, with Jeff Street (OS-64) and Stewart possibly attending.

Highlights

  • Joe's 3D-printed American-sized TS2068 cartridge case (adapted from Claudius's Portuguese-cartridge STL) plus David's matching 128K multi-ROM cartridge PCB with rotary image selector and write-protect switch.
  • Static-RAM replacement daughterboard for the 2068's failing 4416 DRAMs, ported from a Spectrum design using a '574 latch to flatten RAS/CAS into a 14-bit address.
  • Long design brainstorm on a TS2068 successor — preservation-faithful vs evolved — covering storage, video, Spectrum compatibility, the 50/60 Hz interrupt gap, and lack of a 2068 demo scene.
  • Tim relayed that Q68 designer Derek Stuart has offered to redo a TS2068 PCB if the group sends him a dead board; Jeff Burrell's prior FPGA-2068 work flagged as the starting point.
  • Joe diagnosed why the ZX-BesTie internet board never worked for him on a ZX81/TS1000 — it's PAL/50 Hz only, so R30 must be lifted to force PAL mode.

Projects discussed: FPGA "Advanced 2068" Topics: TS2068 / TC2068 · Cartridges, EPROM & dumping · Hardware projects & new boards · Prototypes & rarities · RAM expansion & RAMdisk · ZX Spectrum

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