Well, that's a little odd. Pansonic TVs all pretty much use the same advanced codes, and the button called source or input or TV/Video is Panasonic protocol, device 128, command 5.

The advanced code for that is 61485, but I believe that is the code already built into 1941 (and 0650, the other candidate setup code.)

Can you tell us the name of the button on the original remote that does what you want? Or are you perhaps looking for discrete codes for the input?