What is it?

This is a PCB which replaces the RF modulatorbox of a Sinclair ZX Spectrum computer. It's main purpose is to improve the native video output of the ZX Spectrum by seperating the luma/sync (Y) and chroma (C) signals.

Why did you make it?

The Spectrum's video output quality through it's RF modulator is quite bad on modern LCD's. Even after composite modification, it has terrible dotcrawl. I wanted to get rid of the dotcrawl and improve the video signal, so it is usable on a RetroTink 2X. I know there are alternatives like Spectra RGB and the ZX-HD, but I wanted a more affordable solution.

To sum it up, I wanted to achieve these goals:

• Improve the native video signal;
• Keep the costs as low as possible;
• Get rid of the dotcrawl;
• Replace the modulatorbox and use the standard hole in the case, so case modding is not necessary and make this mod reversible.

I first started with looking at the schematics from the ZX Spectrum, going through datasheets, using Google, etc. After some time I ended up finding this thread on the World of Spectrum forums:

https://www.worldofspectrum.org/forums/discussion/47120/new-video-about-s-video-modification-on-issue-two-48k-spectrum/p1.

(Credits to RGA24 and 1024MAK for providing the basics for this PCB design).

What makes it special?

This little PCB replaces the RF modulator, however the modification to the ZX Spectrum is fully reversible. The old RF modulator and capacitor C65 can both be reinstalled on the PCB for authenticity purposes.

It works very well on a RetroTink 2X through it's s-video input. The resulting image is quite good on my LCD.

Older LCD's or CRT's with s-video input should also work with this modification, results may vary though. It depends how the Spectrum’s nonstandard video signal is being interpreted by the display.

For the ZX Spectrum's native video output, it is quite good. No dotcrawl, vibrant colors and it works with standard s-video leads.

What do I get? The s-video modulator replacement PCB is available as a full kit with printed build instructions or as a fully assembled and tested unit.

Note: For those who are experiencing dark colors on previous revisions, remove resistor R2 & R3. This will make the colors a lot brighter.