Binary Dinosaurs Computer Museum
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French FrankenZX81
THIS is a rarity. When this was pointed out to me it came with an exclamation, WTF IS THAT. Looking at the auction pics it was obviously a ZX81 board but in an old Data Precision 3500 multimeter case (thanks John Honniball!) with a keyboard from Some Sort Of ASCII Terminal. It was in France. I had to have it, and by luck while I was watching the auction and dithering the seller reduced the price by £30. Sold.
The seller sent it massively well packed in an old fruit box, but unfortunately didn't put any padding on the bottom and at some point the whole thing was bounced resulting in severe damage to most of the edge connectors, boards left at odd angles inside. The only thing that saved the first RAM board was that it was physically bolted to the case while the 2nd board and beautiful wire wrapped ROM board weren't. Thankfully with a bit of patience and glue I was able to fix it up as good as new.
It's a ZX81. But it's been expanded with a pair of 16K RAM boards and a ROM board containing amongst other things a pair of EPROMs for the keyboard support, a Fast Loader ROM and a 3rd one that I've not really dug into yet, they're all available for download at the bottom of the page. Investigations on the keyboard (thanks to @sm0rvv on Twitter) showed it to be from a Luxor ABC80 series, and later work by @Devilish_Design discovered the same series of keyboards was used with the Infoton I1200 terminals. Someone went to a lot of effort to avoid using the membrane keyboard on this beast.
Working with the excellent inhabitants of the SinclairZXWorld forum (@1024MAK in particular) we investigated the RAM boards. There's 2, one of which looks like either a copy or prototype of the other. Labelled 'Mic-Rob' and 'RAM 16K' the soldermasked version is wired to be 0-16K while the hand built version has an extra chip to intercept the A15 line so is therefore 17-32K. We couldn't see a reason why I couldn't plug the soldermasked card into a regular ZX81 so that's what I did, quickly discovering a normal ZX PSU couldn't cope. Running the system from a bench PSU with 16V however sprung it into life and worked nicely. The ZX81 board itself had no RAM so I separated it from everything else, heatsinked the ULA and gave it a pair of 2114 RAM chips, that sprung into life too. This gave me confidence to plug the whole thing back together and run it up.
No such luck though, with everything hooked up none of my TVs or monitors could lock onto the signal. The video line came from a board that was half suspended in mid air and I wondered if it was a SECAM timing board and pulled it. This got me a TV signal, and with my trusty TZXduino I could happily load 16K games and utilities.
The stock ZX81 ROM has been altered, but only slightly. RAMTOP has been changed to 48K and the COPY-D* routine originally for the ZX Printer has been hijacked so whatever this machine did it did it via the LPRINT command. The ROM marked FLM is a Fast Loader, there are a pair of ROMs to control the keyboard and one marked ZXE000 which I haven't fully dug into yet. Again they're linked down there if you fancy having a go yourself.
ROM chip on the ZX81 itself.
Unknown EPROM on the ROM board.
Fast Loader on the ROM board.
Keyboard ROM
Keyboard ROM
All ROMs in a handy ZIP file.

All images and text © Adrian Graham 1999-2021 unless otherwise noted using words. Also on