AV Mod in a ZX81

[Bubu]

Jarl, torpedos!

Hi, all!

I've got my ZX81, and a color CRT 14'' TV. I can watch the picture but I have to set the bright to the maximum value, as if not then a nice full black screen is shown. I've heard that that's due to the back porch signal, and can be solved with an AV mod.
Which AV mod is simplest and best at the same time? The fewer components to install the better. I do AV mods in Zx Spectrums 48K without a component at all, just resoldering 2 cables, but, what about the ZX81?



Thank you!

[1024MAK]

My preferred composite video module with back porch generator is the ZX8-CCB from PokeMon. This module also has noise removal circuitry so produces a nice clean and sharp picture. He is a member on the Sinclair ZX World forums. Here is his most recent sales topic. His website and online shop is here. I’ve not bought from his shop, but have bought lots of these from him before he set up his shop.

Next up, is the ZXVid, available here. I have not bought or used this type. But the designer, manufacturer and seller are all good and reliable people.

Finally, there are various sellers on eBay and elsewhere that sell modules based on a design by Joulespercoulomb that uses a 555 monostable timer chip. Some are better than others, see this topic where I helped a member with fault finding such a board.
Note that these do not have any noise removal circuitry.

There are also various composite video modules where there is just a transistor buffer. These do not help if the ULA in your ZX81 does not generate the back porch part of the video signal. More about the different ULAs here. Or if you prefer, you can build your own based on this design.

Mark