(This is not so much a blog post as a public service announcement, because I spent several hours looking for this information , and now that I have the solution, I would like to put it in a place where a search engine can get at it.)
Perhaps, dear stranger who happened upon this page by searching for rca stb766c ir codes, you are trying to set up your new TiVo to work with a digital converter box you purchased at Target. It has RCA printed on the bottom of it, so you choose that when the TiVo asks you what brand your converter box is. And then you go through the infrared setup so that the TiVo can change the channel when it wants to start recording something - and NOTHING HAPPENS. And you're about ready to tear your hair out.
Here is what you do: You will notice on the TiVo page that lists which converters are compatible with their service, they list a box with a model number very similar to your RCA STB7766C: the Venturer STB7766G. You know what? It turns out that that's close enough!
So go back through your channel changing setup and say your box is a Venturer instead of an RCA. I can't guarantee that it'll work for you, but it worked for me. I hope this helps you.
P.S. Just in case you were wondering, stranger who did a search for rca stb766c ir codes, I am not a tech head. Everything I know about this issue I learned from Googling various configurations of my problem. If this does not solve your problem, I PROMISE YOU, I will be unable to help. I apologize in advance, and I suggest you try browsing the help forums at tivocommunity.com.