Sinclair ZX80 / ZX81 / Z88 Forums

This has been driving me mad off and on for a while. My +2 grey has patterns of wavy pixels that slowly move down the screen (and the odd other 'static' like pixel in other places). They show as being behind the boot menu window and I also noticed that when the screen is mostly displaying black, they go away. I've carried out every video mod that I can find, from swapping transistors to the right way round, removing the audio signal etc.

Anyone got any other suggestions?

(btw it's outputting RGB video which is converted to VGA by a QL-VGA device... but even with an RGB>Scart connection it does the same thing.

Is the interference black, or does it include other colours?

Mark

Hello Mark.

It is just black, but as you can see in the pic, part of the wave (like a shadow of the wave) is grey.

Actually, some of those other random pixels that aren't part of the wave do look to be other colours don't they, and there are also other coloured pixels within the wave. I've made a video:

https://www.dropbox.com/s/k3wff7gghwbth ... 0.mp4?dl=0

I'm not sure but it seems there is a faulty capacitator at the IC 2 (TEA 2000). Maybe C45 (1nF), C47 (1nF), C32 (330pF) or C3 (10nF).

Tiger wrote: ↑Sun Sep 20, 2020 12:33 am I'm not sure but it seems there is a faulty capacitator at the IC 2 (TEA 2000). Maybe C45 (1nF), C47 (1nF), C32 (330pF) or C3 (10nF).

Thanks Tiger, I'll check/swap those out and see what happens.

Also possible is interference in the 12V power line - check C41 (100µF) an C23 (22µF). But 'cause I never owned an +2 I'm not sure...

Suppose it can't hurt to do all the electrolytics.

I changed C45, C47, C32 and C3 - no difference. C41 seemed to be way out (25µF instead of 100) so thought that may be an issue - changed it and C23, no change. So I swapped out all the electrolytics and it's still got the same fault.

There did used to be an occasional jumpiness of the pic, particularly the copyright message... that seems to have gone now but it's still not nice to use.

If you enter the 128K or 48K editor, does this make any difference to the symptoms?

Also if possible can you use your RGB to SCART lead, at least until the fault/problem is found.

On that subject, have you tried it on another display?

Mark