Assuming you are in North America, there are four setup codes listed at
www.hifi-remote.com and the Radio Shack 15-2104 has them all built in. This remote is being closed out for $10 and it has a jp1 plug.
The closest TV I could find was a 48RC9313 and it uses TV_0150 the main Mitsubuishi TV setup code.
So if it isn't one of those four setup codes you can buy or build an interface cable and learn some commands (if dog hasn't eaten the OEM remote) and figure it out and do an upgrade.
Failing that you can use some of John Fine's new decoding tools and decode Pronto files and cml files and hope to find the answer.
-Jon
