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Re: Lardo buys another zeddy

Posted: Mon May 04, 2020 9:46 pm
by Lardo Boffin
So its been a while for a zeddie... Or two.

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An early, bugged ROM issue one.
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And a later, non-bugged ROM issue one.
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Re: Lardo buys another zeddy

Posted: Mon Jun 08, 2020 12:05 pm
by Lardo Boffin
A very nice boxed working issue 3. Won’t be able to do much with it for a while though - I have run out of ZX8-CCBs.

35FC8D25-EA2F-499A-BD47-0B46C33A4CCD.jpeg

Re: Lardo buys another zeddy

Posted: Mon Jun 08, 2020 1:35 pm
by 1024MAK
Ahh, one with a stick on hard key keyboard.

I had a Zeddy with one of those, but the stick on hard key keyboard fell off! :lol:

Mark

Re: Lardo buys another zeddy

Posted: Mon Jun 08, 2020 2:12 pm
by Moggy
Lardo Boffin wrote: Mon Jun 08, 2020 12:05 pm A very nice boxed working issue 3. Won’t be able to do much with it for a while though - I have run out of ZX8-CCBs.


35FC8D25-EA2F-499A-BD47-0B46C33A4CCD.jpeg
At this point Pokemon sighs and tells his wife he will be working late as Lardo has run out of video boards. :lol:

Looks good by the way but that early filesixty is a bugger to keypress compared to the later neoprene version.

Re: Lardo buys another zeddy

Posted: Mon Jun 08, 2020 2:36 pm
by Lardo Boffin
Moggy wrote: Mon Jun 08, 2020 2:12 pm
Lardo Boffin wrote: Mon Jun 08, 2020 12:05 pm A very nice boxed working issue 3. Won’t be able to do much with it for a while though - I have run out of ZX8-CCBs.


35FC8D25-EA2F-499A-BD47-0B46C33A4CCD.jpeg
At this point Pokemon sighs and tells his wife he will be working late as Lardo has run out of video boards. :lol:

Looks good by the way but that early filesixty is a bugger to keypress compared to the later neoprene version.
Sadly (for me at least) his shop is shut! My last batch of 5 ‘ccbs ran out a couple of weeks ago. First world problems I guess.

I just noticed that about the keyboard - it needs a lot of pressure!

Re: Lardo buys another zeddy

Posted: Mon Jun 08, 2020 2:40 pm
by Moggy
Lardo Boffin wrote: Mon Jun 08, 2020 2:36 pm
Moggy wrote: Mon Jun 08, 2020 2:12 pm
Lardo Boffin wrote: Mon Jun 08, 2020 12:05 pm A very nice boxed working issue 3. Won’t be able to do much with it for a while though - I have run out of ZX8-CCBs.


35FC8D25-EA2F-499A-BD47-0B46C33A4CCD.jpeg
At this point Pokemon sighs and tells his wife he will be working late as Lardo has run out of video boards. :lol:

Looks good by the way but that early filesixty is a bugger to keypress compared to the later neoprene version.
Sadly (for me at least) his shop is shut! My last batch of 5 ‘ccbs ran out a couple of weeks ago. First world problems I guess.

I just noticed that about the keyboard - it needs a lot of pressure!
Damn I didn't know that he had shut down. Pity it isn't a later back porch ULA then at least you could do the transistor mod. :(

Re: Lardo buys another zeddy

Posted: Sat Jun 13, 2020 1:42 pm
by Lardo Boffin
Moggy wrote: Mon Jun 08, 2020 2:40 pm
Lardo Boffin wrote: Mon Jun 08, 2020 2:36 pm
Sadly (for me at least) his shop is shut! My last batch of 5 ‘ccbs ran out a couple of weeks ago. First world problems I guess.
Damn I didn't know that he had shut down. Pity it isn't a later back porch ULA then at least you could do the transistor mod. :(
It produces a reasonable and bright picture on my CRT telly although as I type it gets worse. I will try and tune it a bit in the modulator (it has helped on occasion) but if not I may need to give it a go. Do you have a link please?

Re: Lardo buys another zeddy

Posted: Sat Jun 13, 2020 2:40 pm
by Moggy
Hi Lardo.

This is perhaps the most simple transistor mod (see picture) and also Mark has a superior design that can be found in his signature. On the output it's recommended to add a 100uf,at least 16Volt rating, electrolytic cap(+ side facing the transistor) for DC blocking although most TV's already do that, better safe than sorry. For the 100ohm resistor I use a variable one as the tiny road-star TV I use overloads terribly with normal settings and bleeding more of the signal to earth/ground helps enormously.

This can be made up on a piece of Vero board with the same four wire (video in-5volt-video out-earth) setup as karls video board jobby and mounted in side the modulator(if removing original c/board) in the same manner using the modulators power and video feed from the motherboard after de-soldering the modulators own feed wires and using the modulators output socket .

However this setup does not produce a back porch signal and is really only any good with the later 210 ULA's as far as colour CRT TV's are concerned though ok with B/W.

Also for the transistor I find that if you have a scrap 81 motherboard with no hope of redemption then either of the two onboard transistors work perfectly for this application.

The board looks a little like this example but imagine an extra cap on board(not sure why the 5th wire is added in this example).

Re: Lardo buys another zeddy

Posted: Sat Jun 13, 2020 7:49 pm
by Lardo Boffin
Thanks Moggy!

Re: Lardo buys another zeddy

Posted: Sat Jun 13, 2020 8:29 pm
by 1024MAK
:arrow: ZX81 Video Transistor Buffer Amp ;)

There is also a design using a NE555 timer chip to generate a pulse for the back porch. I’m not tried it. Alternatively, there is the ZXVid.

Mark