ZX81 ZXvid Upgrade

Background, installation and review of the ZXvid upgrade for the ZX81 - replaces the TV RF modulator circuit board with a new board that outputs a composite video signal and cleans up the signal to resolve the 'back porch' problem.

[@AlastairMontgomery]

Remember having a RAM expansion module like that one :)

[@shaunmorgan2202]

That's my memory of 80s computing too, small computer, tons of wires!

[@redhawk668]

I had the Sinclair RAMpack, it would wobble when I was typing in a program and crash. Very annoying. Well, now that I am skilled in electronics, I designed a little PCB to upgrade the RAM internally. Works good and the expansion connector is free for other stuff.

[@kensmith5694]

I had the ZX80 which used many chips instead of the one big one. The total chip count was 13 IIRC. I made my own RAM expansion and also made a kludge that allowed me to run the ZX81 PROM or the ZX80 PROM. The kludge involved using a bigger PROM and controlling one address wire with the switch.

[@Wobblybob2004]

"Hook and loop fastener" That's worth a subscribe. :-)

[@robertor2535]

Also for me the zx81 was the first computer. Thank you for the interesting video and the very clear and complete explanation.

[@nialldaly7108]

Good Video, Had the ZX81 back in the day, bought the 16K wobble pack and Printer for it and it worked OKish, very annoying when typing a large game from ZX Computing or Sinclair User for a brother or sister to walk in the room and trip over the power cable and pull it out. 16K ram pack wobbled but blue tack semi sorted it. Later Purchased the 32K memotech Ram Pack and memotech keyboard. Still works, But now if I want to play a ZX81 game I use Eightyone Emulater on the PC and load the P files. Plug in the Real 81 from time to time to keep and make sure it s still working. I have just watched another ZX81 video where the presenter changed the ULA, Composite Video and put a modern CMOS 16K ram Chip place of the 1K Chip but had to leave out some pins and run Bodge wires (4 or 5) to the appropriate address lines,. He cleaned up all connections and also took out the V Reg and put in a BukConvertor instead. All fitted on the origonal PCB, As the V Reg was no longer there, there was also no need for the Alu Heatsink. He did however place a heatsink on the ULA. and his girlfriend repainted the ZX81 red after washing the case wiped off the red paint. This was finished with Boat varnish to protect that part.

[@BM-jy6cb]

Brings back memories of trying to program ZX81s in WHSmiths. They were truly awful functionally, but lovely aesthetic design and a superb example of building something down to a price (same with the original Spectrum). The affordability got a lot of kids on the first rung of the programming ladder though, and they certainly deserve their iconic status.

[@rlk54]

I used to own a ZX81 with a 64K RAM pack. It was great fun.

[@nialldaly7108]

I might be wrong but even if you use 64K, did the ZX81 only see 48K. just something that was in my head from 40+ years ago. Any one else, please correct me if I am wrong.

[@himselfe]

Looks like there's just enough space on the top of the ZX81 case to fit a 5" or maybe 7" lcd. Would make a nice little compact mod if you wired it so you only need one power cable plugged in. In fact, given the monochrome nature and speed of the ZX81, a partial refresh e-paper display would probably be perfect, though that would probably require some serious hacks to integrate. Still, a portable ZX81 with a e-paper display on the top would be pretty neat.

[@Komagb]

The very ending had me thrilled and excited for you to escape as though I was 9 years old! And I never had a ZX81!

[@lsbyte]

I still find it slightly scary when he steps round a corner in front of you. I think the lack of sound heightens the tension as you only get the descriptive clues at the bottom!

[@tenminutetokyo2643]

You can also replace the DC regulator with a modern one and then dump it and the heat sink.

[@rog2224]

The Memotech kit was really good, but the 64K did seem to make the ZX81 overheat. I replaced the small aluminium heatsink with a full width copper plate of about the same gauge, and the crashing stopped.

[@Alex_Valentine]

Good to know.

[@MrLurchsThings]

Great video mate 👍

[@richardhowarth1659]

Great video, I loved my ZX81 and enjoyed programming it in my spare time, which was I had a lot of at 11. I remember that curved view at the top with a long listing on my Phillips portable tv, so maybe it the timing from the ula rather than your mod?

[@ZombieVision]

This is indeed a very nice & comfortable video. Thanks mate for explaining everyting so detailed. This clip really inspired me to work on my ZX81.

[@bob19611000]

I jumped from my ZX81to a C64 to get a usable printer output. Went from my C64 to C128D for the 80 columns / MSDOS disk format compatibility (1581). Then went full IBM compatible for the modem speed, etc. Actually would have hung on to the ZX longer because I mod the video and added a real keyboard early on so that part wasn't a problem

[@markaffleck4622]

Good video and very well presented

[@spinnetti]

I used that one too. While in there, why not change out that hot 7805 with a buck converter?

[@Titousensei]

Thumb up for the HP calculator in the background!

[@lsbyte]

I do have an HP-48SX and a 48G, too, but they've not got any screen time yet!

[@K-o-R]

Regarding the difficulty of soldering to the case of the modulator: it may be that there's simply too much mass to heat up properly and allow the solder to flow. It might be easier to drill a hole and use a nut and bolt to secure that wire (it looks a bit too small to fit a fork or ring connector so trapping it might be the best bet).

[@lsbyte]

I often find soldering on to something big is not so difficult because you don't need to heat the whole thing, but just the solder on the tip of the iron. Once applied, it can cool down quickly. Getting the solder off, though, can be a massive pain as you do need to heat the metal. If it's really big, I sometimes attack the lump with some pliers to remove chunks of it first. The desoldering station I bought for the Commodore 128DCR c0pperdragon mod was really useful, though, as I could heat up parts an then just gradually suck it up. I'm not sure what the problem here was, as it was so long ago, but seem to remember the metal just didn't stick to the solder, so maybe it was coated with something, or perhaps the large surface area cooled the solder as I tried to apply it. I'm certainly not great at soldering, although I have got slightly better sine then. The screw idea, though, is a good one, I think, thanks (not that I'm planning to do this particular job again!).

[@kcinplatinumgaming2598]

lol you know non of sinclair's stuff ever worked properly unless we modded it or stuck blutac on the back lol - actually my first computer i taught my self to program was the zx81 .. hours and hours of coding and hand written my code on to lined paper all them years ago.. I finally bought a zx spectrum 128+2 from littlewoods catalog fro 179.99 lol until i bought my own very first cpm system the tatung einstein from dixons which cost of special offer 109.99 that really got me started but zx81 certainly put me in the right direction

[@Spider_Rico]

Could you replace the 1k ram chip with one that was 32 or 64k?

[@vanhetgoor]

It would not fit into the same space on the PCB. It is possible to solder another memory chip piggyback on the present one, except for one connection that goes to another new component. The memory could be doubled in that way, but it would be messy. And it is a lot of work. On the PCB one connection had to be disconnected and rerouted. I would not recommend it. Sometimes it worked.

[@redhawk668]

It is possible to have more than 16KB on the PCB, that will need reshuffling address lines and some more logic.

[@nialldaly7108]

@@vanhetgoor Yes you can fit, CMOS 16K will fit in the socket but you will need to bend out a few address line pins and solder them directly to the Address lines on the PCB- best place to find the appropriate lines is down by the bank of diodes. Check out the guys Videos on His ZX81 upgrade "The Byte Attic"

[@Alex_Valentine]

Does this kit also work for the North American Timex Sinclair 1500?

[@lsbyte]

Sorry, no idea! Might be worth contacting Mutant Caterpillar, who make it. Is that your 1500 from BiTD? Those Timex versions always sounded mysterious, to us in the UK: The 8-bit Guy did a review of the Timex 2068, which seemed very odd!

[@papafrank7094]

As far as I have seen, I think it only went up to the Timex Sinclair 1000.

[@SimonFittonDavies]

Good video. I have 3 of these things and was planning to build the video mod using instructions from JoulesPerCoulomb. I also have an internal 16k RAM upgrade for an issue 1 which I also haven’t gotten around to installing yet (too much stuff, so little time :) ). Would like to see what other ‘junk’ you have to show us.

[@ste76539]

That 'K' is definitely white fella. You can tell it's white by looking at the colour of it, which is white. It's the box it's in that's black.

[@Havanacuba1985]

My WH Smith zx81 from WH Smith came with a memotech 16k ram pack

[@lsbyte]

My ZX-81 also came with a Memotech from WH Smith, but it broke after a few months. When they replaced it, I got a Sinclair one, which wasn't as good (although it wasn't broken, so I suppose that was a major improvement!).

[@gazzaka]

Pity the RAM is not socketted !

[@lsbyte]

That would cost money!

[@gazzaka]

@@lsbyte yea a penny or so lol, but could save money from fault returns