Grüezi from Switzerland

Introduce yourself to your fellow forum members - what was your journey into the Sinclair world?
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crock
Posts: 1
Joined: Tue Nov 22, 2016 6:48 am

Grüezi from Switzerland

Post by crock »

Grüezi mittenand (hello everyone)

I'm a Brit, living in Switzerland for some years now. I only really got into the retro-computing hobby about 6 years ago when I retrieved all my own stuff from my childhood from my parents loft. Commodore is unashamedly my passion, but unlike the trend in much of the world today, I choose to celebrate diversity instead of being afraid of it.

What I came to realise is that we, meaning the UK, had a wonderful range of options during the early days of the home computer revolution that much of the rest of the world was unaware of. Of course the ZX81 sold under the Timex branding in some other countries, but many of the other machines are virtually unknown. To celebrate this, I had an exhibit at last weekend’s Vintage Computer Festival Zurich, where I had a ZX80, ZX81, Oric-1, Jupiter Ace, and a BBC Model-B. You can see some of them

The ZX80 was acquired in an 'unknown' state two years ago and I was over the moon when I finally plugged it in last week to see it worked! The relatively modern CRT of course struggled without the back-porch, but it was usable if I cranked up the brightness. I have one ZX81 still in an un-assembled kit, one in mint but semi working condition and 5 others acquired as a job-lot of spares with a variety of faults, some just with a failed keyboard, others completely dead.

Excluding the one in kit form I would like to get at least two fully working units. It's clear that I can replace keyboards but I'm a bit unclear as to what the state is regarding replacing the ULA, there seems to be a few threads discussing successful replacement but not yet anything commercially available. Is that correct?

regards, Rob Clarke
dr beep
Posts: 2060
Joined: Thu Jun 16, 2011 8:35 am
Location: Boxmeer

Re: Grüezi from Switzerland

Post by dr beep »

Welcome,

A simple interface for modern tv's is available. Someone here will help you later.

As for retrogaming, take a look on all new games developped after 2000>

Johan "dr beep" Koelman
sirmorris
Posts: 2811
Joined: Thu May 08, 2008 5:45 pm

Re: Grüezi from Switzerland

Post by sirmorris »

Welcome!
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gammaray
Posts: 590
Joined: Sun Apr 17, 2016 2:44 am
Location: Texas

Re: Grüezi from Switzerland

Post by gammaray »

Howdy!
5-TS1000,UK ZX81<-Sheelagh, US ZX81, 2-TS1500/KDLX , 3-TS2040 printer, 2-TS2020 cassette decks, ZXPAND+AY, ZeddyNET, ZXBlast, UDG, ZX8CCB, AERCO, BUILDS/REPAIRS ZX Spectrum, ZX80 Minstrel, ZXMAX48 v1 v2, 2-TS-2068, ROM, 16kRAM
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1024MAK
Posts: 5103
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Grüezi from Switzerland

Post by 1024MAK »

Welcome on board Rob!

:D :D :D

Hello and welcome to Sinclair ZX World :D.

The ZX80 and the first ZX81s were designed to work with black and white / monochrome televisions. They work well with these sets.

But it's not so simple with colour TVs. They may produce a poor contrast, very dark picture on some colour receivers. This was fixed when Sinclair changed the ULA chip to a later revision. This later chip includes the "back porch" waveform in the video signal. There are three versions of the ZX81 ULA. Only the last version produced includes the "back porch" circuitry. More info here ;)

Despite what people think, some LCD TVs will produce a reasonable picture from the UHF output of ZX80 or ZX81 computers with one of the earlier revisions of ULA chip. As will some colour CRT TVs. The problem is that until you try it, there is no way to know. I have a Sharp Aquos LC-19D1E-BK colour LCD that works fine with all my ZX81s.

There's loads of stuff on the web and on this forum about modifying a Zeddy for composite video out. Of course, a simple circuit cannot "fix" the missing "back porch" problem. Here is one of my posts showing a composite video out design.

If you can solder, there are modules available from time to time (two different modules from two different sellers) on www.sellmyretro.com that can allow a ZX81 or TS1000 to produce a cleaned up bright clear monochrome composite video signal that is acceptable to colour receivers.

The two modules are:
‬ZX8-CCB (developed from the ZX81-CCP). Buy here.
and
ZXVid

Note that I don't sell either of these.
Please ask if you would like more information.
crock wrote:...but I'm a bit unclear as to what the state is regarding replacing the ULA, there seems to be a few threads discussing successful replacement but not yet anything commercially available. Is that correct?
A few years ago, a stock of the last revision of ULAs was found. But, I these are likely to have all sold out now. See "List of ULA availability". A number of people have remade versions using modern(ish) programmable logic chips, and Andy made a version using 74 series logic chips. But, no, there are no new replacements available for sale as far as I know.

Keep in mind that a faulty ZX81 is not always due to the ULA having failed. The SRAM chip(s) can fail, as can the Z80 CPU or the 7805 voltage regulator. EPROMs have failed. ROM failure is much less common.

If you are want a professional repair service, this is one provider.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
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