I'm having plans to maka a DC VGA box with the help of this schematic http://www.gamesx.com/grafx/dricas.gif (http://www.gamesx.com/grafx/dricas.gif) but I'm a litte curious about the two ICs in it, are they needed? They seem to do something with the H and V sync and are turned on or off ore something like it by the VGA switch. Isn't the H and V sync the Dreamcast outputs correct for a VGA monitor or what does the IC's really do? Not that I couldn't complete the VGA box without them but I'm curious.
There's only one IC, and it is needed. It's just a buffer, it essentially regulates the sync and brings it up to spec.
The IC is split into two halves for clarity, but it's really one chip (note the numbering).
It doesn't look like it's doing a whole lot...it just blocks the sync when the switch isn't closed. I probably wouldn't bother with it myself.
The other consideration is voltage. Older VGA monitors can't handle non-TTL voltages very well, and the native Dreamcast signal may deviate from 5 volts just a bit. Most of the third-party VGA boxes regulated voltage tightly to ensure compatibility. If your monitor or display was manufactured after 1998, you ought to be in decent shape. Note that there were Dreamcast VGA cables available in Asia that had no significant circuitry or chips beyond the video connector.
-KKC, stirring up trouble at work.
Thanks for all the answers, I'll try building the circut without the IC first and test it. If it works I'll be happy with that, if it doesn't I'll order the IC and build rebuild it as the schematic says. Now I'll just have to find a suitable DC cable to rebuild, or would it be easier to change the connector on the Dreamcast... probably not. If I had more skills with a soldering iron I would mount a VGA connector on the back of my system, but I don't know if I could do that now.