Author Topic: EEVblog #872 - Mailbag  (Read 14834 times)

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Online Fungus

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Re: EEVblog #872 - Mailbag
« Reply #25 on: April 27, 2016, 10:46:49 am »
Those were the days - when you could save 20 pounds on a home computer by soldering it yourself.

That's how I got my first computer. Soldered a ZX81 when I was 8.  Damned thing even worked.

Eight? Damn, that's young. I must remember that next time somebody tells me that their kid is too young for dangerous toys like soldering irons.
 

Offline rrinker

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Re: EEVblog #872 - Mailbag
« Reply #26 on: April 27, 2016, 12:19:21 pm »
 What's crazy is that only a few years before you could buy the fully assembled TS-1000 for $99, I had built my first computer, which cost $106 plus extra for the address displays, and it didn't have a full keyboard, only a hex keypad, and LED displays. It had video output, but with the mere 256 BYTES of memory, the best you could do was 64x32 resolution, and part of what showed on the screen included a graphical representation of the code generating the picture. For ANOTHER $100 the following year I added the expansion board which gave it a whopping 4K of memory (still no BASIC or anything more than a monitor routine). Now you could do 64x128 graphics and not have to display the program. Approximately 2 years later, the TS-1000 appeared at the $99 price point. Leading up to that, I seem to recall the ZX-81 being offered at around $130, or $99 for the kit.
 Some of the other accessories I remember are both external 'proper' keyboards and one product that clipped over the case and gave moving keys that simply pressed down the existing membrane switches when struck. There may have been an intermediate product, or maybe it was just one of the full keyboards, that required you to open up the computer and pull off the flex cable from the stock keyboard and plug in its cable in place.
 

Online Fungus

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Re: EEVblog #872 - Mailbag
« Reply #27 on: April 27, 2016, 12:44:01 pm »
What's crazy is that only a few years before you could buy the fully assembled TS-1000 for $99, I had built my first computer, which cost $106 plus extra for the address displays, and it didn't have a full keyboard, only a hex keypad, and LED displays. It had video output, but with the mere 256 BYTES of memory, the best you could do was 64x32 resolution
The ZX81 was popular because:
a) It was cheap
b) It connected directly to a TV and had a cassette port
c) You could copy cassettes easily - free games! (unlike Ataris and TIs which used uncopyable cartridges*).

Most "computer clubs" of that era were just groups of people with a bunch of cassette recorders connected together for copying stuff.

(*) Yes, I'm sure some of you guys would have been able to copy cartridges but most people couldn't.
 

Offline stmdude

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Re: EEVblog #872 - Mailbag
« Reply #28 on: April 27, 2016, 02:41:02 pm »
That's how I got my first computer. Soldered a ZX81 when I was 8.  Damned thing even worked.

Eight? Damn, that's young. I must remember that next time somebody tells me that their kid is too young for dangerous toys like soldering irons.

There were different standards back then. I still have some scars from learning how to solder.  :)
I don't think a "modern" parent would accept that.

The ZX81 was popular because:
a) It was cheap
b) It connected directly to a TV and had a cassette port
c) You could copy cassettes easily - free games! (unlike Ataris and TIs which used uncopyable cartridges*).

You missed one.  The manuals for the Sinclair computers were _really_ good (for its time). I learnt BASIC from just the literature included with the ZX81.
 

Online Fungus

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Re: EEVblog #872 - Mailbag
« Reply #29 on: April 27, 2016, 02:58:34 pm »
You missed one.  The manuals for the Sinclair computers were _really_ good (for its time). I learnt BASIC from just the literature included with the ZX81.

Yep. I forgot that one.

http://zxnext.narod.ru/manuals/ZX81_Manual.pdf

Stephen Vickers was a top manual writer.
 

Offline robin7g

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Re: EEVblog #872 - Mailbag
« Reply #30 on: April 29, 2016, 01:01:42 am »

I have a mint example right here - Memopak 16K by Memotech Ltd.

The velcro stuck on the back of Dave's one suggests it may have had one too.

I remember buying my first ZX81 in WHSmith's for 20 quid (heavily discounted) sometime in the mid 80s.

RE: Memotech RAM pack.

It did!! Sharp eyes. I took the Memotech RAM pack off before I sent it. Sorry Dave.   :o
 

Offline robin7g

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Re: EEVblog #872 - Mailbag
« Reply #31 on: April 29, 2016, 01:18:47 am »
This is the original Sinclair RAM pack with the wobbling problem. The ZX81 under it started life as a kit. The circuit board tracks are all wavy hand routed ones which is the issue 1 layout.
 

Offline rrinker

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Re: EEVblog #872 - Mailbag
« Reply #32 on: April 29, 2016, 01:24:48 am »
 Found what I was looking for. I remember buying this magazine. I just read the one on the top left, VOl 3 #5, and remember that issue specifically. Check the ads for add-ons. All SORTS of stuff. And there are at least 2 adds for the stick on top keyboard I mentioned, plus others that were full external keyboards.

https://archive.org/details/syncmagazine

Memotech was one that had a full line of accessories, not just memory expansion. This issue also has a small item on doing the direct composite output - same circuit that was included in the package sent to Dave.


 

Online Fungus

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Re: EEVblog #872 - Mailbag
« Reply #33 on: April 29, 2016, 09:28:45 am »
This is the original Sinclair RAM pack with the wobbling problem.

The 'problem' is that it's a crap connector with an unsupported, unbalanced plastic box connected to it. Any type of vibration will wobble the connector, including normal typing on the keyboard.

Magazines at the time were always full of fixes for RAM pack wobble - rub your PCB contacts with hard pencil erasers, put blu-tack between the RAM pack and computer, use strips of velcro, build up the PCB contacts with solder to get a tighter fit, etc. None of them really worked. Sudden memory loss was a fact of life.
 

Offline smithnerd

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Re: EEVblog #872 - Mailbag
« Reply #34 on: April 29, 2016, 01:52:13 pm »
What's striking about the Memotech RAM pack is how well made (and designed) it is.

It's obviously a custom aluminium extrusion, which can't have been cheap to make. The fit and finish is superb.

 

Offline Arlen Moulton2

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Re: EEVblog #872 - Mailbag
« Reply #35 on: April 29, 2016, 03:37:25 pm »
hey dave, how much would it cost for you to send one of the sinclairs to the uk?
amoulton
 

Offline blackbird

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Re: EEVblog #872 - Mailbag
« Reply #36 on: April 29, 2016, 06:24:20 pm »
Ah the ZX81, brings back good memories, one of the first computers I've used when I was 7 years old. The next year I got the ZX Spectrum as my birthday present (age eight). At school they could not believe my parents gave me a 'real' computer.  :-DD They had only one computer at the administration department.
 

Online Fungus

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Re: EEVblog #872 - Mailbag
« Reply #37 on: April 29, 2016, 07:19:20 pm »
hey dave, how much would it cost for you to send one of the sinclairs to the uk?

Probably more than just buying one in the UK: http://www.ebay.co.uk/sch/i.html?_nkw=zx81


 

Offline robin7g

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Re: EEVblog #872 - Mailbag
« Reply #38 on: April 30, 2016, 01:39:05 am »
What's striking about the Memotech RAM pack is how well made (and designed) it is.

I remember as a kid getting the 16K Memotech RAM Pack because it was cheaper than the official Sinclair one. I think I was 8 years old. The Memotech was and is better than the official Sinclair RAM pack. Just better in all respects. But knowing what I know today I wish you could have just got  32K Static RAM and solder it in.  All of that faffing about with ram packs.

http://www.zx81.de/english/32k-rame.htm

I think the ZX81 was a lot about programming and hacking them and adding their own stuff. I remember typing in programs for magazines and a kid in my neighbourhood build a full size keyboard and wooden case.
« Last Edit: April 30, 2016, 01:45:27 am by robin7g »
 

Online Fungus

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Re: EEVblog #872 - Mailbag
« Reply #39 on: April 30, 2016, 01:00:15 pm »
What's striking about the Memotech RAM pack is how well made (and designed) it is.
I remember as a kid getting the 16K Memotech RAM Pack because it was cheaper than the official Sinclair one. I think I was 8 years old. The Memotech was and is better than the official Sinclair RAM pack. Just better in all respects.
Not least because it was longer and you had more options to fix it firmly to the back of the computer.

But knowing what I know today I wish you could have just got  32K Static RAM and solder it in.  All of that faffing about with ram packs.
The connector they used was one of the worst possible choices.

But ... it was also the cheapest. It literally adds zero cost to the base hardware - just traces on the PCB and a hole in the back of the case..

Maybe they could have added a couple of self-tapping screws to screw it onto the back of the machine or something. I dunno.  :-//
 

Offline Arlen Moulton2

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Re: EEVblog #872 - Mailbag
« Reply #40 on: April 30, 2016, 03:03:58 pm »
hey dave, how much would it cost for you to send one of the sinclairs to the uk?

Probably more than just buying one in the UK: http://www.ebay.co.uk/sch/i.html?_nkw=zx81
dave sent me the motherboard out of that tablet for free and that is the same size as the zx81.
amoulton
 

Online Fungus

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Re: EEVblog #872 - Mailbag
« Reply #41 on: April 30, 2016, 07:24:13 pm »
hey dave, how much would it cost for you to send one of the sinclairs to the uk?

Probably more than just buying one in the UK: http://www.ebay.co.uk/sch/i.html?_nkw=zx81
dave sent me the motherboard out of that tablet for free and that is the same size as the zx81.
Postage was free?
 

Offline Brumby

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Re: EEVblog #872 - Mailbag
« Reply #42 on: May 01, 2016, 02:22:55 am »
Postage was free?

How to start an argument on eBay....  ;D
 
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Offline Arlen Moulton2

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Re: EEVblog #872 - Mailbag
« Reply #43 on: May 02, 2016, 08:04:10 pm »
hey dave, how much would it cost for you to send one of the sinclairs to the uk?

Probably more than just buying one in the UK: http://www.ebay.co.uk/sch/i.html?_nkw=zx81
dave sent me the motherboard out of that tablet for free and that is the same size as the zx81.
Postage was free?
then the postage will be free on this!  :scared:
amoulton
 


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