The ZX81 was never designed for modern televisions. That's why if you've ever tried connecting your ZX81 to an LCD, you'll probably have seen a very dark or very pale screen.
This modification, based on a design by Andy Rea, fixes that! The reason for the poor display is that the ULA (the custom chip) doesn't give a properly compliant signal, so the TV can't tell what's white and what's black. The ZXVid contains a video encoder chip that makes a properly compliant signal, improving the ZX81's signal immeasurably.
The ZXVid board replaces the innards of the TV modulator so there are no changes to the outside of the ZX81. Connect your ZX81 up using the cable provided to the "video in" port of your TV (or SCART converter block) and see the ZX81 better than when it was new!
This version of the ZXVid comes on its own, ready to be transplanted into your ZX81's current modulator casing. Remove the old PCB in the modulator, put in your new ZXVid PCB in its place, and enjoy the results! Please note the modulator can be quite fiddly to modify, so if you're at all unsure we suggest purchasing our ZXVid modulator replacement or the composite modification service.
See the ZX81 like you've never seen it before - The ZXVid gives you that chance!

Fitting instructions for the ZXVid can be found here:
http://www.rwapsoftware.co.uk/DOC/ZXvid_Manual.pdf