Ultimate64 problem with S-Video on Scart

Found the core problem: Many new LCD screens do not support S-Video signal over scart, internally the luma & chroma will be mixed into composite… 🙁
I tested it on 2 different screens..

Ultimate64 – S-Video

I was testing my new scart auto selector ( external powered) and I only got black/white screen (luma signal) on my Salora display. I know it can handle s-video, becaused I used several other devices with s-video on this display.

So is it the display or the scart switch ?

I tried another manual scart switch ( passive, no external power ), and again black/white.
So it seems it is not the switch.

I tried a C64 breadbin.. and we got color..

C64 Breadbin – S-Video

What is different between the Ultimate64 and a C64 breadbin ?

Let’s do some measurements

I made a little cable with only luma, chroma and ground so I can attach that to my scope.


purple = luma
blue = chroma
grey = gnd

Measurement of C64 Breadbin

CH1 = luma, CH2 = chroma
ch1 max: 1.34~1.36V
ch2 max: 1.56~1.64V
ch1 & ch2 div: 500mVDC

Measurement of Ultimate 64

CH1 = luma,CH2 = chroma
ch1 max: 1.02~1.06V
ch2 max: 0.84~1.02V
ch1 & ch2 div: 500mVDC


Reported findings to Gideon.