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Old 5th Mar 2022, 12:39 am   #1
BBCmicro
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Default 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.
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Old 5th Mar 2022, 1:37 am   #2
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Default Re: Zx81

I'm sure it is a typo but the regulator in a ZX81 is a 7805. ��
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Old 5th Mar 2022, 2:20 am   #3
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Default Re: Zx81

Quote:
Originally Posted by BBCmicro View Post
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!
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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Old 5th Mar 2022, 2:33 am   #4
SiriusHardware
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Default 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.
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Old 5th Mar 2022, 1:10 pm   #5
electronicskip
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Default 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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Old 5th Mar 2022, 3:44 pm   #6
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Default 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.

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Old 5th Mar 2022, 4:15 pm   #7
BBCmicro
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Default Re: Zx81

Quote:
Originally Posted by Mark1960 View Post

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.
It's a nice thing to have and definitely makes the machine more useable

Quote:
Originally Posted by SiriusHardware View Post
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.
It's an edding 751 red paint marker, a couple of quid off amazon. It did a nice job - picture attached. I will look into the internal upgrade - I love the industrial design of the ZX81 and although nice to have, RAM packs do spoil the looks a bit!

Quote:
Originally Posted by G6ONEDave View Post
I'm surprised that the ZX81 is not fitted inside the keyboard casing, like the spectrum add on keyboard was designed to do.

Dave
Yes I was a bit surprised, there would be enough room in the case and would negate the annoyingly short ribbon cable (which is too short to allow you put the keyboard in front of the ZX, only beside)

Quote:
Originally Posted by wave solder View Post
I'm sure it is a typo but the regulator in a ZX81 is a 7805. ��
Yes good spot.
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Old 5th Mar 2022, 5:03 pm   #8
SiriusHardware
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Default Re: Zx81

Quote:
I didn't realise Memotech had a ram pack for the ZX81.
They made arguably the nicest ZX81 RAM packs as they were the only ones designed to continue backwards on the same physical lines as the ZX81 as Rick Dickinson had originally envisaged that the official RAM packs would. They also made some of the biggest (Memory capacity wise) - up to at least 64K as far as I remember although not all of that memory would have been directly available to BASIC.
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Old 12th Mar 2022, 11:56 am   #9
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Default 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.
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Old 12th Mar 2022, 1:53 pm   #10
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Default Re: Zx81

Quote:
Originally Posted by Eidolon View Post
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.
Those fold out leaflets for the ZX81 are great it looks so slick with the photography - that is one think Sinclair got right!

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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Old 13th Mar 2022, 4:24 pm   #11
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Default Re: Zx81

Quote:
Originally Posted by Timbucus View Post
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.
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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Old 13th Mar 2022, 6:08 pm   #12
BBCmicro
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Default Re: Zx81

Quote:
Originally Posted by Timbucus View Post
Those fold out leaflets for the ZX81 are great it looks so slick with the photography - that is one think Sinclair got right!
Sinclair definitely had flair for eye catching design. Calculators, ZX80 & 81, I wonder if Sir Clive's emphasis on looks as portrayed in Micro Men is close to truth or came from marketing dept more generally.

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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Old 13th Mar 2022, 6:28 pm   #13
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Default 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.
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