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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment. |
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5th Mar 2022, 12:39 am | #1 |
Tetrode
Join Date: Aug 2006
Location: Dundee, Scotland, UK.
Posts: 53
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Zx81
Received a parcel of goodies from Wireman on Wednesday and have enjoyed tinkering with the Sinclair ZX81.
All in working order, even the original membrane eyboard which is something unusual! I have a DC-DC switching regulator on order to replace the old 7808 which runs very hot. I'll also pop a heatsink and some thermal grease on the ULA to keep it going. Just for fun I built a little circuit from a diagram I found online (I can't remember where) to invert the video signal to white on black. UHF looks quite good on the little 4.5" alba TV which is all I have at the moment - although it does give a crick in the neck - I might have to find something more suitable later on. The external keyboard is quite interesting - a few dead keys but traced to broken traces around one keyswitch. Oddly they seemed fine visually and the solder joints were good - perhaps the flux had etched through in the ring around the keyswitch pins? All working now though. The keyboard goes through a 'keyboard buffer' module but it does no such thing, typing has to be carefully paced otherwise keystrokes are missed. Advertising speak! A spot of red oil-based felt pen revived the ZX81 logo nicely. All in all it's a fascinating machine built to a cost and I'm looking forward to getting to know it better. |
5th Mar 2022, 1:37 am | #2 |
Hexode
Join Date: Feb 2007
Location: Chesterfield, Derbyshire, UK.
Posts: 481
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Re: Zx81
I'm sure it is a typo but the regulator in a ZX81 is a 7805.
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5th Mar 2022, 2:20 am | #3 |
Octode
Join Date: Mar 2020
Location: Kitchener, Ontario, Canada
Posts: 1,265
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Re: Zx81
I think back then “keyboard buffer” didn’t mean the same as it does now. Just an electrical signal buffer. Definitely jealous of that keyboard, probably very rare accessory even back then and nice to see it survive the years since.
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5th Mar 2022, 2:33 am | #4 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,483
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Re: Zx81
I would be interested to know the exact brand / type of the red pen you used to refresh the logo with?
Have a look around for articles describing how to fit 16K RAM internally, it's quite cheap and easy to do and is also easily reversible. I realise you got a Memotech RAM pack with the machine but fitting the memory internally makes the little machine usable and wobble free while maintaining its neat appearance. |
5th Mar 2022, 1:10 pm | #5 |
Nonode
Join Date: Oct 2010
Location: Gloucester, Glos. UK.
Posts: 2,149
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Re: Zx81
I diddnt realise Memotech had a ram pack for the ZX81.
Remember rummaging around in the bins at Memotech in Witney when i was a kid for computer bits discarded.
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Oh I've had that for years dear!! |
5th Mar 2022, 3:44 pm | #6 |
Octode
Join Date: Dec 2019
Location: Owston Ferry, North Lincolnshire, UK.
Posts: 1,689
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Re: Zx81
I'm surprised that the ZX81 is not fitted inside the keyboard casing, like the spectrum add on keyboard was designed to do.
Dave
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Quote "All is hyperthetical, until it isn't!" (President Laura Roslin, Battlestar Galactica) |
5th Mar 2022, 4:15 pm | #7 | |||
Tetrode
Join Date: Aug 2006
Location: Dundee, Scotland, UK.
Posts: 53
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Re: Zx81
Quote:
Quote:
Quote:
Yes good spot. |
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5th Mar 2022, 5:03 pm | #8 | |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,483
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Re: Zx81
Quote:
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12th Mar 2022, 11:56 am | #9 |
Hexode
Join Date: Dec 2012
Location: Worcester, Worcs, UK.
Posts: 257
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Re: Zx81
I bought an old book in a charity shop last week, and it had a nice little ZX81 sales flyer from WHSmith folded up inside. A nice little bit of nostalgia to keep with my old Spectrum games catalogues.
I've yet to try out the ZX81 emulator/personality on the Spectrum Next yet, I'd like to see how well it actualy runs 81 software. |
12th Mar 2022, 1:53 pm | #10 | |
Octode
Join Date: Mar 2019
Location: Barry, Vale of Glamorgan, Wales, UK.
Posts: 1,362
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Re: Zx81
Quote:
The Next ZX81 emulator is very good and really gives a great support for loading .p files. One day someone may do an FPGA personality for it but, for the moment it has been great to recover and look at some of my old programs on the Next from the ZX81. |
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13th Mar 2022, 4:24 pm | #11 |
Hexode
Join Date: Dec 2012
Location: Worcester, Worcs, UK.
Posts: 257
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Re: Zx81
Things seem to have stalled a bit on the Next, regarding alternate cores etc, there's quite a few things that don't work properly still. I'm assuming that all of this is down to the KS2 version that's being worked on, and hopefully not long afterwards, that we'll have proper working versions.
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13th Mar 2022, 6:08 pm | #12 | |
Tetrode
Join Date: Aug 2006
Location: Dundee, Scotland, UK.
Posts: 53
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Re: Zx81
Quote:
I've ordered some thin plywood to try and make some sort of case for the system to try and keep it tidier and easy to put away when finished. All reversible of course! |
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13th Mar 2022, 6:28 pm | #13 |
Dekatron
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,483
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Re: Zx81
I have an original mint-condition ZX Spectrum version of that leaflet / insert / pamphlet, the quality of photography and presentation was first class, as Tim said.
It sounds like that little system has found itself a good home anyway, BBCmicro. |