[Elecraft] K2 tuning issue

[Alan Slusher]

I have an older K2/10 (serial 868) which has worked very well for years.
Today I suddenly became aware of a problem: I can't change the frequency 
using the tuning knob (yes, I did check the frequency lock).
The final frequency number on the display blinks (eg: the "4" in 14301.24) 
(happened to have been listening on the 14.300 net) but no number changes 
when the frequency knob is turned, and the radio's frequency does not change 
either.
No problem with frequency change using direct frequency entry (the two band 
buttons followed by the frequency numbers),
and the RIT works just fine.
I did the 456 reset before reading the instructions about saving the CAL FIL 
numbers, with the result that I guess I will have to go back through that 
procedure (I now have to punch in 14301 and use the RIT to move to 14.301.24 
to listen on 14.300, had been spot on before).
The K3 next to it and the Kenwood 430 below it continue to work just fine 
off the same two antennas (a vertical and an 80m dipole - both through 
tuners).

Does anyone have any idea what I am doing wrong?
Any help would be highly appreciated.

Alan V31FA.