Scrambled functions, remote problems

Hi

I have a strange problem with an RCA DCR6300N, unit has been woking perfectly, then suddenly the remote no longer works (remote tested and is ok), the function buttons on the unit itself are fine on the DVD side, but are "scrambled" for lack of a better word on the VCR side, where the IR sensor is located. The eject button now does nothing, the DVD/VCR button ejects the tape, channel up is record, channel down is channel up, and the record button toggles the unit between DVD and VCR. So basically, the only function that is missing is channel down.
All the switches are ok, I can find no cold solder connections, it has been unplugged for long periods to reset, all voltages appear to be where they should be, as far as I can tell without service info.
Any suggestions would be greatly appreciated.