Sinclair ZX80 / ZX81 Forums

[iturbez]

Well, well. I've put my hands on my Zeddy... The first attempt: making composite video mod (1 transistor, 1 resistor and 1 capacitor). I fit it into the Zeddy. It works! But... My ULA is 2C184E... VERY DARK SCREEN! I've read some web pages, and all of them say "2C184E ULA will make a bad picture"...

Is there anything I can do, or may I change this chip with newer one? (I've seen them on eBay, with or without a heatsink)

Thanks in advance.

[Mike3]

What parts did you use... and yes you can replace the ULA ... I used a 2N2222 and a 100 ohm resistor and no cap... actually I have on some ZX81's disconnected the RCA out from the modulator and just ran a wire from the Video to it.. and had great results...

Regards... Mike

[siggi]

Hi
one of the German ZX-Team members solved that problem. Here is the (German) description:

http://www.sps-wagner.de/Sonstiges/zx.html

Siggi

[iturbez]

Thank you all, folks.

The scheme I've used is this:




I´ll try the scheme Siggi posted, when I receive the IC. I'll tell you something...

[XavSnap]

HI,

You had to pull all Tv settings to top levels. (brightness to the top level )
The signal is too low, and you had to amplify it.

Have a look to:
http://zx81.ordi5.free.fr/brico/video/
or
http://zx81.ordi5.free.fr/brico/video/video%20par%20peritel.djv

[iturbez]

XavSnap:

Thank you very much. I've been looking at the schemes at the link you've posted. Can you tell me what does each of the circuits? I guess you are thinking "video par peritel" is the simplest one...

I'm getting crazy with all of this... When I plugged my first Zeddy (a long, long time ago), things were all very much easier...

EDIT: I can´t find any reference about TEC2014... What's it?

[sirmorris]

Get a new ULA. Job done

[XavSnap]

Hi,
Is there anything on the UHF modulator ?
If nothing, your ULA is destroyed.
8-(

[iturbez]

Get a new ULA. Job done

Yes! You were right! Now, my Zeddy is fully working!



Next step: 32K RAM mod...

[sirmorris]

Yaaay!