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Commodore 128 to Video Converter

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RobClaggy:
I have a Commodore 128 (that of course has two outputs, an RGB, and a composite.  I bought a GBS-8200 video converter to allow me to connect the C128 to newer monitors and such.  This is the second different type of converter I have bought!

None of them seem to work.  I mean, the CGA side is no big deal.  But I want to output the RGB signal on an LCD HDTV that I own.  When I plug the RGB into the 8200 I get just lots of lines and distortion.  Nothing I can really make heads or tails out of.

So with that a bust I tried a different tactic. When I look the GBS-8200 manual, it quite clearly shows how to wire the RGB direct into the pins on the harness.  So I chopped up an old RGB cable I had and soldered the pins directly.  Same exact thing.  Lots of lines and distortion and no signal.

Can someone shed some light on what I am doing wrong here?  I don't see any other configuration options that are relevant.  I know both the monitor and the C128 are working!  I guess the converter could be bad, but my first one (different brand even) didn't work either.

james_s:
What kind of monitor are you using? There is more than one type of RGB. The RGB output on old computers used separate lines for each color and one each for horizontal and vertical sync. The RGB input on some monitors that uses three RCA connectors is luminance and sync on the green one and then difference signals for red and green. If you get garbled lines you might not be getting the sync.

m k:
Lots of lines and distortion feels more than no signal.

Since input and output are both RGBHV only sync fequency seems to be a possible precepted problem.
(NTSC vs. PAL is probably not the one)

The link below indicates that the needed input is RGBC when GBS-8200 booklet has modes YUV/RGBS/RGBHV.
(RGBC and RGBS are equal, RGsB is SoG)

https://sites.google.com/site/h2obsession/CBM/C128/rgbi-to-vga

Benta:
The GBS-8200 actually only supports analog RGB, not digital as with CGA.
A resistor network to do the level shifting is possible.

RobClaggy:

--- Quote from: Benta on November 19, 2021, 08:07:55 pm ---The GBS-8200 actually only supports analog RGB, not digital as with CGA.
A resistor network to do the level shifting is possible.

--- End quote ---

Wait.  Can you explain this in a little further detail?

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