Not Atari, but definitely 8bit (ZX81)

Any 8bit repairs, images, cool things, upgrades etc.
PeteW
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Not Atari, but definitely 8bit (ZX81)

Post by PeteW » Mon Aug 06, 2018 7:12 pm

A friend just donated this to me from their loft clear out. A boxed ZX81, with 16k ram pack, manuals, an early 80s set of computer course magazines and some tape software!

No idea if it works or what repairs it might need, but I'll give it a go :)

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20180806_191028.jpg (157.28 KiB) Viewed 388 times
20180806_190434.jpg
20180806_190434.jpg (67.32 KiB) Viewed 388 times

Petari
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Re: Not Atari, but definitely 8bit (ZX81)

Post by Petari » Mon Aug 06, 2018 7:23 pm

I had it back in 1983. Bought as kit, and assembling took about half hour. If I remember correct, only some 5 ICs :D
Z80, ROM, 1KB RAM and ULA + power regulator.
There is 2 kind of people: one thinking about moving to Mars after here becomes too bad, the others thinking about how to keep this planet habitable.

PeteW
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Re: Not Atari, but definitely 8bit (ZX81)

Post by PeteW » Mon Aug 06, 2018 7:26 pm

I'm looking forward to the amazing games - they'll be just like the pictures on the front of the cassettes right?!

PhilC
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Re: Not Atari, but definitely 8bit (ZX81)

Post by PhilC » Mon Aug 06, 2018 8:24 pm

I had one of those back in 1981 and have another now which I have to get round to testing. You'll need an old crt tv, preferably with manual tuning to get that to work , or do the composite mod. Apparently the video signal is rather basic and won't sync to a modern tv.

PeteW
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Re: Not Atari, but definitely 8bit (ZX81)

Post by PeteW » Mon Aug 06, 2018 8:28 pm

I was going to try this mod for getting a picture on a modernish tv:



I'll test the power supply and then try plugging it in and see what happens. Not for a couple of weeks though - one project at a time :)

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Re: Not Atari, but definitely 8bit (ZX81)

Post by PhilC » Mon Aug 06, 2018 8:45 pm

Good luck, let me know if the mod works as I'll need to do something similar :D

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Re: Not Atari, but definitely 8bit (ZX81)

Post by stephen_usher » Mon Aug 06, 2018 8:58 pm

That's a very late ZX81, so it should have the ULA which produces a reasonable display. (The early one forgot to add a bit at the beginning of the scan line which is used to gauge the black level. This meant that all colour TVs (and some B&W ones) showed a very dark display.)

I notice that the manual isn't ring-bound either. Probably to make it cheaper.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
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PeteW
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Re: Not Atari, but definitely 8bit (ZX81)

Post by PeteW » Mon Aug 06, 2018 9:05 pm

Looks like it's from late 1982 - the programming guide is a 1982 print and the software catalogue is the December 1982 edition. Is that a late model? I'll be honest I know little to nothing about the zx81 at this time!

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Re: Not Atari, but definitely 8bit (ZX81)

Post by rubber_jonnie » Mon Aug 06, 2018 10:51 pm

stephen_usher wrote:
Mon Aug 06, 2018 8:58 pm
That's a very late ZX81, so it should have the ULA which produces a reasonable display. (The early one forgot to add a bit at the beginning of the scan line which is used to gauge the black level. This meant that all colour TVs (and some B&W ones) showed a very dark display.)

I notice that the manual isn't ring-bound either. Probably to make it cheaper.
I have a very poorly ZX81 that suffers from this very problem, the display is just about unreadable, even on a period TV.

Something else I need to fix, but I have too much Atari stuff going on :shock:
Collector of old Atari things:
800XL + Ape Warp mod, 2x 1010 cassette, 1050 + Happy mod, 65XE (128k) & XC12, SIO2SD, 2600jr, 7800 and Lynx II
Atari 520ST (1Meg) + Gotek, 1040STFM + Vortex ATOnce + Gotek, 1040STF long button floppy, 4160 STE with Gotek and ROM switcher, 4160STE with 32Mhz booster, ROM switcher and CosmosEx, not to mention various bare ST boards for testing including a PAK 68/2 :)
Plus the rest..
Amiga stuff, Mac stuff, Sinclair stuff etc...
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Re: Not Atari, but definitely 8bit (ZX81)

Post by IngoQ » Tue Aug 07, 2018 7:02 am

While you're at it, check the 5V Regulator, these things were not very reliable. In my Speccy 128k I have replaced the 7805 with a L78S05CV, which allows more current and is cooler at the same time. My "toastrack" is now only a handwarmer ;)

And if you want to replace the power supply, check the polarity of the plug, these are reverse to what you might be used to. Afterwards check the polarity. And while you're at it, recheck the polarity ;)

If you're looking for enhancements, you can find some cool ones (like flash storage i.e.) here: https://www.bytedelight.com
Ingo :geek:

“Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away.” - Antoine de Saint-Exupéry

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