New Member Hello & Question

Introduce yourself to your fellow forum members - what was your journey into the Sinclair world?
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16kramwobble
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Joined: Tue Nov 02, 2021 7:43 pm

New Member Hello & Question

Post by 16kramwobble »

Hi - my first ever computer was a ZX81 in March 1981. I was 14. Duran Duran had their first hit. Ronald Reagan survived an assassination attempt. Charles and Di were eengaged. Now many years later I have a ZX81 again. Nostalgia is a big factor, of course, but also there is unfinished business: to get into machine code. I never did at the time: by Christmas I had a Vic-20 (the less said the better). Anyway I hope to find some kindred spirits here.

My question: I'm having trouble hooking up the little baby to a TV. I have bought some older second hand TVs (a Matsui yesterday) but they don't tune in to CH37 - or more accurately the signal from the ZX doesn't seem strong enough.

Any advice on what I'm doing wrong or what I need to do or what TVs you recommend. I know it's a basic question (geddit!), but appreciate any help.
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1024MAK
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Re: New Member Hello & Question

Post by 1024MAK »

Hello and welcome to our forum 16kramwobble!

:D :D :D

The modulator in a ZX81 is totally analogue. Although it’s output frequency is supposed to be on TV broadcast channel 36, it may actually be anything between channel 35 and 37. It may not be exactly on an official frequency either, so use the fine tune control (if applicable).

Check that the RF cable is okay. If either the inner conductor or the outer screen/braid is broken, you won’t get a good picture.

It’s worthwhile cleaning the video output socket on the modulator, to ensure that you get a good connection. Use IPA or another ‘electronic’ solvent cleaner. Then use an eraser/rubber (the type designed to remove pen are better than those for pencils).

The next thing you need to be aware of this, there are three different ULA versions. The earlier two versions don’t include the part of the video signal known as the ‘back porch’. Most (but not all) colour TVs (including old CRT types) use this part of the signal to auto calibrate to set the contrast and brightness, as it is supposed to set the black video level. Because these two ULA versions don’t output the correct level at this point of the video signal, the result is the displayed image is very dark and has poor contrast.

Sinclair corrected this with the last ULA version. More details here.

Try another TV, to see if that makes any difference.

Are you getting any picture at all?

I hope you enjoy this forum :D

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

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16kramwobble
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Re: New Member Hello & Question

Post by 16kramwobble »

Hi Mark, thanks for your reply. I will clean the output socket, but I guess the analog output was never designed to work with modern TVs, and that the older the TV the better the picture quality, although I note your post about the different versions of the modulator. So, I will try to source more old TVs. Which one do use?

Dumb question warning. I suppose you cannot convert the UHF signal to scart or rca to make it more compatie with s modern TV.
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mrtinb
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Re: New Member Hello & Question

Post by mrtinb »

That requires the Chroma 81 interface, but that is unavailable for order at the moment.

http://www.fruitcake.plus.com/Sinclair/ ... erface.htm
Martin
https://zx.rtin.be
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube
16kramwobble
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Re: New Member Hello & Question

Post by 16kramwobble »

Wow! What an amazing extension. Any ideas when it might be available (and cost) or is it discontinued?
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BarryN
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Re: New Member Hello & Question

Post by BarryN »

mrtinb wrote: Tue Nov 02, 2021 10:18 pm That requires the Chroma 81 interface, but that is unavailable for order at the moment.

http://www.fruitcake.plus.com/Sinclair/ ... erface.htm
Or there are some circuit mods with transistors, etc, to do B&W composite video output.
Ravenger
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Re: New Member Hello & Question

Post by Ravenger »

BarryN wrote: Wed Nov 03, 2021 1:32 am Or there are some circuit mods with transistors, etc, to do B&W composite video output.
This is what I've got in my refurbished ZX81 that I bought via Ebay. The output is astonishingly sharp - way better than the fuzzy, ghosty picture I remember on the B&W TV I had back in 1982.

The only problem is due to the way the ZX81 processes video during loading you don't get the loading or saving bars - just a blank screen, which is a shame as that was part of the experience I was hoping to see again when getting a 'new' ZX81.

Still it's very cool to be able to play the old games I used to play and type in a few example programs. It's like having a time machine - I feel instantly transported back to those school days. Some wonderful memories of the early days of computers, going into Smiths and seeing all the games on display and going around friends houses to play on their Spectrums (which I couldn't afford myself, hence the ZX81). Attending the early computer shows was also cool.
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1024MAK
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Re: New Member Hello & Question

Post by 1024MAK »

Please don’t assume that all modern TVs don’t work. I use a Sharp LCD TV with my 1980s computers including ZX81s with RF UHF outputs.

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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BarryN
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Re: New Member Hello & Question

Post by BarryN »

1024MAK wrote: Thu Nov 04, 2021 1:17 am Please don’t assume that all modern TVs don’t work. I use a Sharp LCD TV with my 1980s computers including ZX81s with RF UHF outputs.

Mark
I have the 210E version of the ULA and it works fine with my 65 inch flat screen TV.
16kramwobble
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Joined: Tue Nov 02, 2021 7:43 pm

Re: New Member Hello & Question

Post by 16kramwobble »

How can I tell what version of the ULA I have? I assume I lift the lid and it's physically stamped on the unit?

I have got other micros to work with my TV through the scart connection. But with the ZX81 the TV looks like it is about to find the picture but it is very dark and extremely unsettled and the channel tuner (whether auto or manual) cannot secure it.

On another TV (LCD) the picture is found but it is unstable - things will start to wobble after a few minutes and I have to adjust the fine tuning.

Any ideas? Is it a poor ULA?
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