What to do with an unusual ZX81?

[daveyj67]

Hi all

So I bought another zeddy as spares/repairs on Ebay for a bit of tinkering with the intention of adding a composite mod and internal 16K RAM upgrade. However, when I opened it up to take a look I found that it was an early version with the stand-off board on the Z80 to rectify a ROM error as discussed here and on pictures attached:

viewtopic.php?f=7&t=1387

I gather that only 20,000 of these were produced back in the day, so I guess it's quite rare now. Anyway, I fired it up with temporary connections to the composite mod and up came the K prompt with a good clear picture. The keyboard appears original and works fine too.

So that led me to thinking, should I leave this zeddy as is and maybe sell it on to someone looking for a rarer version and get another one to tinker with rather than potentially damaging it with my "upgrades"?

All opinions gratefully received.

Dave

[Lardo Boffin]

I have come across a few of these but haven’t ever refurb’d one. Not ridiculously rare but I wouldn’t change one other than any necessary repairs.

There are probably a few in here!

https://www.sinclairzxworld.com/viewtop ... f=8&t=3312

[Moggy]

My own personal view is there are more users than collectors out there, myself included. The kludged ones are still deficient ROM wise and any I have come across over the last forty odd years I have happily rejigged. Improve the bugger and let someone enjoy it as it was meant to be enjoyed without worrying about floating point errors and a lousy TV picture.

As far as collectability goes they are Hardly a Rembrandt or Ferrari so no pension plan there, just a simple old 8 bitter wanting one last day in the sun so improve it and set back in the wild, earning its salt rather than sat in some some bods glass cabinet.

Just my thoughts on it and appreciate that others may think differently.

[1024MAK]

Hmm, being the electronics nerd that I am, I was thinking that those are a useful source of a couple of 74 series logic chips...

Mark

PS i have plenty of run of the mill issue 1 and issue 3 boards to tinker with. A long time ago in a universe far, far away, I bought around 5 not working, for spares/repairs" issue 1 Zeddies from a seller for not a lot of money. It turns out these were from an educational place and apart from the normal keyboard faults, most had simple faults, like the ROM being placed incorrectly in the socket.

[ones complement]

Ah, but isn't this the point where the ones which do survive become more valuable because everyone at the time said 'Nah, nothing special...'. Looking into my crystal ball 20 years from now I can imagine people saying 'Do remember that peculiar mod they did to fix the ZX81 ROM, classic 1980's stuff!. Pity nobody preserved an original one'.

[daveyj67]

Thank you all for your thoughts - some mixed views, a bit like my own mixed feelings It's a peculiar bit of computing history really, I don't suppose Apple, Dell or Lenovo would let a product out of their factories looking like that nowadays

Maybe I'll just do the composite mod so that it can still be used but without changing anything drastic, just a couple of snipped wires leaving all of the video gubbins in place and use it with an external ram pack. Like 'ones complement' says there won't be many survivors to tell the story of eccentric British computer companies if they all get modded!

Dave

[1024MAK]

If it's any help, the ZX Spectrum issue 1 (and some early issue 2) boards that have a different "dead bug" daughter board tend not to be modified (unless they were back in the day).

You don't need to snip any wires. Just desolder the two wires going into the modulator from the PCB and secure them so they don't touch anything else.

Mark

[daveyj67]

Good point, thanks Mark.