Re: C128D to SVGA

From: Marko Mäkelä (
Date: 2001-08-14 07:53:12

On Mon, 13 Aug 2001, Raymond C. Bryan wrote:

> From:
> I purchased a "scan converted" and I have the 128D connected to it using
> the composite signal but it only works in 40 colunm mode.   Unfortunately,
> this scan converter does not have a  9 pin RGB connection but a 15 pin
> connection.

I assume that the scan converter (scan doubler) has a pass-through
interface ("VGA IN" and "monitor out") for the output signal, like the
Redant box I recently acquired.  The signals from those connectors are
probably passed through more or less directly, through some kind of
semiconductor relays.

My scan doubler has three inputs: two for composite video and one for
S-video (separate luma and chroma).  There is no scan-doubling RGB input.
The RGB output from the C128 VDC chip has around 15 kHz line frequency,
while VGA monitors need at least 30 kHz.  So, the VDC signal should be
routed through the scan doubler.

If the IC markings on the device are badly worn (like those on my box, I
guess they have a bad conveyor belt at the factory), then you cannot
easily reverse engineer the scan doubler circuit to add an RGB input.  
The only viable solution would be to build an NTSC/PAL encoder for the RGB
signal.  There are one-chip solutions from some manufacturers.  A friend
of mine (who also got the Redant box) is going to build something.
Hopefully the picture quality won't be too bad when using S-video.


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