Another thing to check before giving in to repair:
I've got a Sony, and the 'ON' pushbutton plastic pushbutton itself hangs-up in the de-
pressed position. You can't always see it, it flexes a little to one side (the plastic pushbutton you depress itself). When that happens, the Channels will not change,
(and most other remote functions won't work).
Take a pin or paperclip, and see if you can release the plastic pushbutton, so it pops
all the way back up. (So it pops straight up, not stuck depressed sideways)
Sorry, if that doesn't do the trick, but it works on mine.