Hmm. It does sound like the cga2rgb part is fried, which isn't surprising if you reverse voltaged it several times.
It might be worth getting hold of somebody who knows a bit more about electronics to test it for you, maybe somebody who has a working setup and could verify if it's dead. I am sure posting it off wouldn't cost much. Short of that you probably need to buy a new one. I can't hock my own product here as it's out of stock pending arrival of parts, but at least when it's back in stock it has the 5v line clearly marked as well as a removable chip should it get blown up.
It might be worth looking for the cheap resistor based solutions. Maybe somebody could knock one up for you, it's no where near as good but at least you would have a picture.
Even less TVs support S-Video than RGB. So what's the reason for converting the 80-column-video to S-Video? Converting 40-column FROM S-Video to RGB would make more sense, I think. Although, seriously, in the long run devices with analogue inputs will be gone altogether, so at some point we have to convert to HDMI.
In Europe that is the case. It turns out most of the Americans have S-Video in and not RGB, so they have been calling for such an adapter.
I agree about HDMI however the chips to do that are horribad. I need to look at learning VHDL and making a small FPGA converter that can encode the HDMI directly from the CGA input. In theory it's not hard at all but in practice I know nothing about FPGA design.
For VDC VGA Mania you will basically just need a RGB Digital to RGB Analogue conversion like the RGBI2RGBA you mentioned or the BIT-C128.com-device (which I use), or the device Pyrofer is offering on Amibay. Then you just need to output this to a 15-pin-VGA-connector.
For my BIT-C128-device I use the "6-Wire Signal Kit for VGA-to-BNC Cable" offered on the same site for $7.50. If you have a different RGB-Digital to RGB-Analogue-converter you may also use this cable: www.ambery.com/db9todbadca.html
This cable I have and whole adapter too. Problem of 15kHz CGA/RGB to VGA adapter is that dark yellow looks like name is - dark yellow, not as orange... this was reason to buy RGBI2RGBA... Ok, I'll contact Pyrofer.
Commodore 64 was great, Commodore 128 is bigger, better, faster and more powerful... Commodore 65 was almost here, but C256 is coming and it will be earthquake...