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 »

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

Post by PeteW »

I'm looking forward to the amazing games - they'll be just like the pictures on the front of the cassettes right?!
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PhilC
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Re: Not Atari, but definitely 8bit (ZX81)

Post by PhilC »

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.
If it ain't broke, test it to Destruction.
PeteW
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Re: Not Atari, but definitely 8bit (ZX81)

Post by PeteW »

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

Post by PhilC »

Good luck, let me know if the mod works as I'll need to do something similar :D
If it ain't broke, test it to Destruction.
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stephen_usher
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Re: Not Atari, but definitely 8bit (ZX81)

Post by stephen_usher »

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.
Collection now with added Macs, Amigas, Suns and Acorns.
PeteW
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Re: Not Atari, but definitely 8bit (ZX81)

Post by PeteW »

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

Post by rubber_jonnie »

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 many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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IngoQ
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Re: Not Atari, but definitely 8bit (ZX81)

Post by IngoQ »

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:

| Atari 1040STE@32MHz | Amiga 1200 (ACA1220) | Atari 800XL (U1MB, SIDE2) | Atari 130XL (Sophia DVI) | C64 (1541 Ultimate II, Rev3 RFMod Replacement) | TI 99/4A (F18A, 32k, FlashROM 99) | Sinclair ZX Spectrum 128 (Stereo, DivMMC) | Amstrad CPC664 (512k, M4 Wifi) | ... |
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stephen_usher
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Re: Not Atari, but definitely 8bit (ZX81)

Post by stephen_usher »

PeteW wrote: 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!
Yes, that's just about the time Sinclair stopped selling them. The price drop shown on the box was probably to shift the last of the stock.
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.
Collection now with added Macs, Amigas, Suns and Acorns.
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