You can use the scandoubler by itself without the CV643d. It should show the even the kickstart screen if working properly.
It might not work properly if it's hooked up to the CV643d and the jumpers are wrong. Been a while since I set mine up so I'm not 100% sure about this.
Also, the scandoubler might be fine. It could be the video slot in the 4000 mobo that's bad...
