Commodore 128 to Commodore 128dS D2 monitor

[Speel]

Hello,
I'm new here to this awesome forum, and I have a question.
I am trying to attach my Commodore 128 to my Commodore 1084dS D2 monitor.
Normally, the 1084dS would accept digital signals, however, mine's a newer model, and doesn't offer digital capability AFAIK. There's no switch on the backside of the monitor, which there is on older models :-/
I opened the monitor, but couldn't find any trace of such a switch, so I can't solder a switch myself.
The Commodore 128 outputs a kind of s-video signal, but when I attach it to the monitor, it outputs bright/dark vertical lines (kinda 'softly').
So either the question is: how do I get rid of those lines, or how do I make an digital RGB to analog RGB converter?
I am quite experienced in soldering, building circuits and programming microcontrollers.

[NeWmAn]

For digital RGB to Analog RGB: Have you looked at rgbi2scart & Cga2scart?
Link: http://hem.passagen.se/tomasf/elektronik/elektronik.html

[Speel]

Thanks
I hadn't found that one yet...
Now I need to learn Swedish (just kidding, I know some swedish ppl)

[viletim]

An active circuit is required if you want 100% accurate colours. Something like this G700 RGB DAC http://gamesx.com/wiki/doku.php?id=av:g7000_av. TTL (C128 is from the mid '80s...must be TTL) is a very loose voltage spec.

[Speel]

Unfortunately, I didn't get the RGB2SCART thing to work. I got at best a shaky b/w signal in 80 lines mode, using the combined horizontal/vertical sync.
I don't know how to set it up in 40 lines mode, Using the composite sync of the digital output or the luma output didn't work. Maybe I should use a LM1881 between it, and use a variable restistance between the input and the output RGB signals.

[Speel]

An active circuit is required if you want 100% accurate colours. Something like this G700 RGB DAC http://gamesx.com/wiki/doku.php?id=av:g7000_av. TTL (C128 is from the mid '80s...must be TTL) is a very loose voltage spec.

C128 has indeed TTL specs...
Hm, the circuit looks interesting. :-) I'll try it later.

[NeWmAn]

I got at best a shaky b/w signal in 80 lines mode, using the combined horizontal/vertical sync.

I can't help you because I don't know much either about the C128 or your monitor, so I'm probably wrong...
But if you are getting a b/w signal your monitor is in composite mode, not in RGB.

[Speel]

No it's in rgb mode.
I just found out that 80 lines mode is only monochrome...
Gotta find a way to set it to 40 lines I guess.
Still have that unstable picture...

[ido8bit]

The 80 column output on a C128 is a 16 color RGBI output.  If you are not getting all 16 colors you've probably wired the intensity pin incorrectly.  If you're not getting ANY color something is seriously wrong with the RGBI->RGB circuit you have built. 

The 40 column output is generated by the VIC-II chip and is only available at the Y/C output. 

[viletim]

Speel,

How are you combining the H/V sync signals? Not with just a piece of wire I hope.

The best method is to XOR the two signals together (74LS86). Use all the spare gates in the package connected in parallel as a buffer.

[Speel]

Sorry for my very slow reply, I've been extremely busy last months. I tried what you've said, combining both signals using a XOR chip (using multiple gates in parallel to be sure). But it didn't work. I just don't get a sync signal now. But I'll try the sync part of this VGA to RGBS circuit to accomplish it.