I've been able to program some things on this TV, but have not found advanced codes that will work for some features. The main ones are PIP Channel up and PIP Channel down. I am very familiar with the information on http://www.hifi-remote.com, and it's for a 15-1994 remote. I have also tried the learning feature (which I have been able to use in the past, but have been unable to program it using this feature). I would appreciate it if someone could help me. Thanks.

If the learning feature has stopped working, it's almost certainly because the learning memory is full. I'm assuming you're not a JP1 user, so you probably have no idea what buttons you have already programmed using learning. Chances are that, over the years, you have used learning to program several buttons that you have forgotten about and don't even use any more.

You could use the 980 reset command to clear out everything that has been learned, but this will also wipe out any keymoves and macros that you have programmed, so only you can decide if that's a good idea or not.

As for the advanced code question, you should really state what setup code you are using to help us, but I think most Mits TVs use the same code, which is TV/0150. I just looked up a file for a Mits TV in the JP1 file section and it has advanced codes 134 and 006 listed for PIP CH + and -, so give those a try.

After I posted that, I thought that maybe I had just used up all the memory.

I did use setup code 0150, and I will try those advanced codes you mentioned. Thanks.