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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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Old 18th May 2017, 3:39 pm   #1
60 oldjohn
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Default Sinclair ZX81

I have two Sinclair ZX81 computers, on one the letters and numbers "ZX81" are in red on the other just highly polished and black, Why? I have a possible theory, but what do you think?

John.

Last edited by Paul Stenning; 18th May 2017 at 5:02 pm. Reason: Title corrected as requested
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Old 18th May 2017, 5:16 pm   #2
julie_m
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Default Re: Sinclair ZX81

I would assume it was a production change; it might indicate whether the machine had the early ROM or the later one, or maybe the red paint just got too expensive. Or maybe the case supplied in the kit of parts to build at home had all-black raised lettering. (My own one was bought ready-made, and had the red lettering ..... Not sure which ROM it had.)

Be nice to know the real reason, though .....
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Old 18th May 2017, 5:35 pm   #3
60 oldjohn
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Default Re: Sinclair ZX81

Quote:
Or maybe the case supplied in the kit of parts to build at home had all-black raised lettering. (My own one was bought ready-made, and had the red lettering ..... Not sure which ROM it had.)
The above is my thoughts, there is one on net for sale with black writing and is a kit. My black ZX81 came from a late friend who would have been capable of constructing one from a kit, but it came to me in a factory box seemingly ready made, but the picture on box shows read writing it also had an 16k Ram pack.

John.
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Old 18th May 2017, 6:02 pm   #4
Craig Sawyers
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Default Re: Sinclair ZX81

The Uncle Clive effect. Back in the day, Sinclair negotiated hundreds of kilos of reject transistors from manufacturers. The staff at Sinclair would test them to find the few percent that worked well enough to go into a product (tiny radio, amplifier etc). Rumour has it that the vast majority of really defective transistors were used as hard core under Sinclair's drive.

At one stage I had a Sinclair Scientific calculator. You could ask it to find the arcsine of an argument greater than +/-1. The LED display would start to flash randomly and intermittently for several minutes - after which a result would appear! Of course such an answer exists - it is a complex number. The Sinclair Scientific knew nothing about complex numbers, however ;-)

I can't remember whether it was the ZX81 or the Spectrum that a mate bought new. He stuck in a programme which included the square root of two. The result was very close to being close, but had an error. He changed it so that it was finding the root of (2.0001) and got a much much closer answer.

Basically to save computing time, they had put commonly used constants into RAM. But they had entered root2 incorrectly! So any programme that used root2 had an error. However if you put in something that was not quite 2, it used an algorithm to calculate it.
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Old 18th May 2017, 9:32 pm   #5
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Default Re: Sinclair ZX81

My ZX81 has the lettering in red, though the red colour is rather uneven. It's been like that since new. Perhaps the process for putting the red colour on wasn't very consistent.

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Old 18th May 2017, 10:11 pm   #6
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Default Re: Sinclair ZX81

Knowing Sinclair, it was even possible they didn't go through QC so no one noticed they had forgotten to paint them.

My ZX81 (car boot sale 1 in 1990) had red painted logo. I was slightly obsessed with them for a bit as it was about the simplest computer you could muster. It was connected to a 9" B&W portable television and an old tape recorder. I miss it. Have no idea what happened to it but it wasn't in my numerous boxes of junk in my parents' loft a few years back.
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Old 18th May 2017, 10:55 pm   #7
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Default Re: Sinclair ZX81

As far as I know the raised ZX81 logo on original ZX81s was ALWAYS painted red, but, being raised, it was prone to being worn off during normal handling. My original ZX81 (bought / built as a kit in 1981) has roughly 85% of its red logo paint intact.

When this happened it made the machine look pretty shabby so people sometimes removed what was left of the half-worn red paint to neaten the appearance of the machine.
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Old 19th May 2017, 1:03 pm   #8
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Default Re: Sinclair ZX81

Both my ZX81s are red, just checked.
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Old 19th May 2017, 1:30 pm   #9
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Default Re: Sinclair ZX81

I'm pretty sure mine had the red lettering, but I no longer have it so can't be sure. I was a graduate student when I bought it and actually managed to get it paid for as a research expense, though I never managed to do any real work with it.
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Old 19th May 2017, 3:41 pm   #10
Dave Moll
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Default Re: Sinclair ZX81

Red here, too.
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Old 19th May 2017, 5:45 pm   #11
60 oldjohn
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Default Re: Sinclair ZX81

I originally thought it may have been to denote kit built being black, now I don't know. Possibly something as simple as just running out of red paint!




John.
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Old 19th May 2017, 5:48 pm   #12
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Default Re: Sinclair ZX81

Mine's red too - however, it's started to flake off on the '1'. So maybe it's just rubbed off?
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Old 19th May 2017, 6:05 pm   #13
60 oldjohn
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Default Re: Sinclair ZX81

Richrussell, The card boxes of the kit sets show black lettering, or else that is what I would think.
John.
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Old 20th May 2017, 3:55 pm   #14
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Default Re: Sinclair ZX81

Hello

It looks as though the forum here https://www.worldofspectrum.org/ is still active so might turn up some info. I think there is anarchive of sales documents, articles etc somewhere on that site too.

Bye
Will
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Old 25th May 2017, 10:33 am   #15
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Default Re: Sinclair ZX81

I owned one from 1981....I currently have two....every ZX81 I ever saw had the "ZX81" raised lettering painted red regardless of whether they were kit or store bought.

However they were prone to having the paint worn off. My first ended up mostly black and I painted the logo white with Liquid Paper.

I prefer red.
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Old Yesterday, 1:00 am   #16
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Default Re: Sinclair ZX81

The two I built from kits when they were sold off cheaply (25 ISTR) in Practical Wireless at the end of production had red lettering (and still work.)
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Old Yesterday, 2:16 pm   #17
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Default Re: Sinclair ZX81

I still have by boyhood ZX81 along with one other I picked up years later.
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