Sinclair ZX80 / ZX81 / Z88 Forums

Hi,
New to this forum and wondering if someone has an idea related to my problem.
Just started up once my old Spectrum 48K.
I’m using the mod for the composite signal.
Computer seems to work fine but there’s clearly noise on the screen. More specific 2 horizontal red coloured lines that split the screen in 3 parts.

Any idea where these lines come from or better I post also a screenshot?

Regards

Hello and welcome

You may wish to say hello and introduce yourself in the welcome area

Yes a photo would definitely help, as I’ve not heard of this problem before...

Mark

Hi all,

In attachment 2 screenshots. Not so easy to take a good picture.
Not sure if this is normal but screen also look very blue. I expected white (or close to that)

looks very mysterious - is it possible to try it with an other monitor or tv? The red lines are looking so perfect - much clearer than the "NEW" prompt

They also exceed the width of the Spectrum's display area too almost as if it was an artifact of the TV rather than a fault with the computer.

Does changing the paper colour make any difference?

Thanks,

Good idea to see the impact of changing paper color.
Will also try on another screen and see the outcome

Is it an issue two PCB? They have adjusters for the colour mix (I have issue two which has a blueish screen) but are not that easy to work with. Apparently an oscilloscope is recommended.

Lardo Boffin wrote: ↑Sun Jan 03, 2021 6:32 pm Is it an issue two PCB? They have adjusters for the colour mix (I have issue two which has a blueish screen) but are not that easy to work with. Apparently an oscilloscope is recommended.

As do issue one boards, but the preset resistors (variable resistors) only change the overall colour encoding. So they affect the white / yellow / blue (etc) colours of the whole screen. But I can’t see how poor adjustment can cause those horizontal red lines.

Although a ‘scope is recommended in the service manual, it’s often easier to set them by eye if you program the machine to show a screen with all the colours.

Later issue boards (three onwards) have different colour bias circuitry and don’t need manual setting up.

Mark

Hi guys,

Yep,
Root cause was the TV. Another one provides a nice screen.
Found out 2 columns of keys not working. Will need to check flatcables...

Compositie signal from my WII works fine on the first TV. Weird it has problems with the Spectrum.
Perhaps better install a composite module than the current wire bridge....