In that case, also pull the two RS PCB off the mother board, remove the chips from the RS board and reseat (Use PLCC Puller or John will yell at you:-)) Reseat everything and try again. IF still intermittent go after the IR sensor, and swap RS boards one at a time.
TRW test with and using another IR RS tender also is a good method of trouble shooting. If you NKP tender works with another Engine, then the NKP engine side is the issue... etc,,,, G