ZX81 Cursor distorted

[Fabrizio69]

Hi all,
I have a ZX81 'quite' restored
I changed the RAM after blank screen and now it works.
I made the modification for video composite with the schema



and it works. The cursor K is clear but distorted horizontally at the centre. Unfortunately I have to change the keyboard and I don't know if the problem is related only on the K line.
Could be a wrong schema for mod composite video? I saw others solution in the web without any capacitor. What do you think? It's the ULA?

Thanks in advance for your opinions and help
Fabrizio

[1024MAK]

It's not the composite video modification. Some ZX81 do suffer from with the top line of text slanting or the bottom line being partly distorted. You would get these symptoms if you were using the RF TV output.

Which version is the ULA? If you don't know what to look for, post up a photo of it.

The early version ULA is more likely to produce these symptoms.

Mark

[Moggy]

Even with a composite mod the top line still does the slanty thing when using a 2C158 ULA if it did it when using the RF output in my experience, even Pokemon's video boards didn't cure it.

[Fabrizio69]

Hi all, thanks for your reply. The ULA is the 2C184E 8234.
The distortion is only on the top and bottom when write the lines or list the program. After the run the output is shown correctly. I post the images.
Do you confirm is the ULA?