When I got my Xbox several months ago, I managed to get 15Khz RGB out of it for use with my RGB box. I made up a cable and hooked everything up. But when I turned it on, I noticed some wavy interference that "grunged" up the picture a little. I had a newer board revision of the Xbox and thought that this was due to the new video chip inside. I managed to tweak the picture to get rid of some of it but not all. I just resigned myself that this was a problem that I may not be able to fix.
At this point I am working on a Component to RGB converter box that will autosync between 15Khz and 31Khz. This box, like my RGB box, gets its power from the console unit using the +5VDC pin within the A/V port of the console. But some of the chips require -5VDC and I found a Negative Voltage Generator design (using the 555 timer chip) to try to get it. When I put the Generator together and added the +5VDC from the Xbox, I would get a lot of interference. Thinking that it was the Generator design itself, I hooked up the converter prototype to a PC digital switching no-load power supply that I got at a local electronics store. I put in ground and +5 from the supply and turned the Xbox on.
The power supply worked and worked quite well. But when I got a stable enough picture, I noticed that the wavy interference (that had also appeared while prototyping the converter) was gone. I then took apart my RGB box, disconnected the +5VDC line that went to the game console, and hooked up the power supply. Then I hooked up the Xbox and turned everything on.
The RGB came up as clean and pristene as I wanted it. The realization then hit me that the wavy interference wasn't due to the new video chip, it was due to the Xbox internal power supply. The +5VDC I was using from the Xbox was very "dirty". This could also explain the problems that the X2VGA box has been having with some of the Xboxes. That device gets it's power from the Xbox just like my projects and it must be dealing with the same interference.
Of course, I have one fix which is my external power supply. But the more optimal solution is to open up the Xbox and fix the internal power supply unit. Can you imagine what this "dirty" power is doing to the rest of the Xbox's internal components? Is there any leads on how to fix the internal power supply within the Xbox so I can clean up the power?