Blurry signal/image with ghost effects (on a 1084S)

[cethewe74]

Hello everybody,

my VC-20 (bought not too long ago) does not offer a good signal on my 1084S. The monitor offers a very good picture with a C64C and an Amiga.
With the iPhone camera, the picture actually looks better / richer than it really is.

You may not recognize it so well in the photos, but in reality you can clearly see a shadow and ghost effect on the left. Overall, it is also very fuzzy / blurry.

On the right side it's very mushy with a yellow tinge on the edge from white to cyan.

You may be able to see it better here in this picture:

OK - I opened the good piece.

I tried to play around with the potentiometer, according to this article: http://sleepingelephant.com/denial/wiki ... djustments
Unfortunately, that does help at all, except that I can make the picture lighter or darker.

Does anyone have any idea what else I could do here?
Thank you!

Many greetings,
-Christian

[Mike]

Hi, Christian,

the effects you show in the pictures are quite normal and partly because of PAL itself (there's always some 'leakage' of colour to the right and down), and partly because of the composite signal as it is mixed in the video circuitry from luma and chroma - this leads to visible pixel tearing, especially with red, green, purple, cyan and orange colours on white or black background. Also, some vertical stripes in the luma signal show activity of the video chip (mostly, bus DMA when VIC is fetching text screen and character data).

You'll find several variants of the S-Video mod discussed here in the forums. This mod keeps luma and chroma separate, and provides the two signals on two repurposed pins of the video socket. Try it out. It really improves the video quality a lot.


P.S. don't turn the red "pot". It's actually a variable capacitor used to fine-tune the master oscillator clock. If that is too far off, the monitor only shows a B/W signal as it doesn't anymore recognise the PAL colour carrier frequency.

[cethewe74]

Ah, OK. Thanks for the great explanation.

Danke dir
-Christian

[MCes]

try also to put in parallel to C8 a low ESR capacitor (not less than 100uF), the type that are used for switching PSU or DC-DC converter: it could minimize the vertical issues in the last part of the left border.

[cethewe74]

Thanks @MCes