ZX81 monitor

Discussions about Sinclair ZX80 and ZX81 Hardware
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gammaray
Posts: 433
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Re: ZX81 monitor

Post by gammaray » Wed Sep 07, 2016 9:42 pm

Double check everything if it makes sense with your computer system. i.e. no USB then no USB peripherals. If you have a HDMI input on your laptop, you could use a video demodulator/convertor to convert RF NTSC to HDMI. (MOST DO NOT)

In any event your are still buying something... Let me know how it works out.

I reserve the right to be wrong and to commit the wrong of being right (correct)!
Finish what you start. Truth is over the mountaintop or six feet under.
4 x TS1000, 2 x TS1500 , 2 x timex 2040 printer, 1/2 x timex 2020 cassette deck, ZXPAND+AY, ZeddyNET, ZXBlast..., unfinished Spectrum...Still no life!

r00t
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Joined: Sat Sep 03, 2016 8:43 am

Re: ZX81 monitor

Post by r00t » Wed Sep 14, 2016 6:16 pm

Hi again:

I've tested the hardware, and it works, but the image quality is really bad.

Maybe it is a matter of fine tuning?

Actually the background color is dark grey instead of white.

I've tried channel 2 and at freq 55.25 MHz

Any ideas?

r00t
Posts: 14
Joined: Sat Sep 03, 2016 8:43 am

Re: ZX81 monitor

Post by r00t » Wed Sep 14, 2016 6:20 pm

Actually, the image could be much better, it's strange, because sometimes it flashes and for a fraction of a second the image is perfect (white background and very clear characters).

I will try to post images/videos. I think with a small tuning, this device could work perfectly.

r00t
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Joined: Sat Sep 03, 2016 8:43 am

Re: ZX81 monitor

Post by r00t » Wed Sep 14, 2016 7:04 pm

Playing with hue/saturation I was able to get a much better picture.

There is still a colorful flickering around the black color of the fonts which I am not able to get rid of.

Attached is a video.

Please tell me your opinions.
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RetroTechie
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Re: ZX81 monitor

Post by RetroTechie » Wed Sep 14, 2016 11:42 pm

Ahh, the joys of RF modulation and an ULA walking on its last legs... (like almost every Zeddy out there) :lol:

Want better? Start with a composite mod! Yeah I can understand if someone doesn't want to touch a ZX81 inside (and -somewhat- agree due to fragile keyboard connectors etc). But hey, that's the basic choice you have: do a bit of internal modding, or live with VHF/UHF crap output. :evil:

r00t
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Re: ZX81 monitor

Post by r00t » Thu Sep 15, 2016 12:27 am

The question is the following:

That's the better quality you can get from a VHF/UHF output or I can get better if I play with the capturing hardware or wired or whatever else?

thanks.

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1024MAK
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Re: ZX81 monitor

Post by 1024MAK » Thu Sep 15, 2016 1:24 am

I'm not sure what you are asking...

But, any UHF or VHF picture will be poor, due to the large number of compromises needed to get a TV picture to fit into what originally was a monochrome picture channel (and there are plenty of compromises for the monochrome picture already...).

The reason you get blurred colour effects, is due to the colour decoder being confused by the video signal translations between "black" and "white" or vice-versa.

If there is an option to turn off the colour decoder, this will improve matters.

But as RetroTechie says, your best option is to convert the Zeddy to output composite video ;)

Mark

r00t
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Re: ZX81 monitor

Post by r00t » Thu Sep 15, 2016 4:00 am

@1024MAK

What I meant is:

I think that the picture I am getting by using this USB adaptor is worst than the picture you get if you plug in the Zeddy to an analog TV set. Or is it the same?

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1024MAK
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Re: ZX81 monitor

Post by 1024MAK » Thu Sep 15, 2016 12:49 pm

I think that vey much depends on the TV. And which version of the ULA chip is fitted to the ZX81 / TS1000.
I have a LCD TV that produces a reasonably good picture via UHF, even with the ULA chip that does not include the part of the video waveform known as the "back porch". Only the last produced ULA has this "back porch" part of the signal.

Older CRT type TVs are/were more tolerant of the non-standard video outputs of retro computers. Some of the more modern colour CRT sets were not happy, with the user having a picture with poor contrast. Some LCD TVs also dislike the video output from Zeddy computers.

And then there is the tuning drift caused by the computer heating up... Some TVs can track the signal, others can't.

Converters typically are more tolerant, as they are normally multi-standard. While some modern TVs may only work with one or two video standards.

Mark

r00t
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Joined: Sat Sep 03, 2016 8:43 am

Re: ZX81 monitor

Post by r00t » Thu Sep 15, 2016 11:20 pm

I am thinking in trying the component mod.

Where I can find an easy one and with a step by step instruction??

It is absolutely mandatory to have solder skills? (then I need to practice first and get a solder and all the corresponding stuff).

thanks.

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