The Kawai & Teisco Analog Synths Group

Dear Members, Hello; my name is Clive. I have a Kawai SX-210, my
problem is when i first switch on it continues to play a single cord
as if the key hold was switched on, after about half an hour it
disappears and everything works as normal, what do you think is
causing this phenomenon?. Incidentally if i reprogram the unit with
the tape program everything works fine  until i switch off the
unit;when i switch back on the problem reoccurs. Can you help?. 
          I do have an original manual and factory sound program tape
if anyone wants a copy.
        Also could you give me an idea as to how much the SX-210 is
worth theses days as i may have to sell it due to arthritis. 
 
Regards, 
 
Clive.