Technics SL-CH550 CD player "no disc"?

I have an Technics SL-CH550 CD player that don't play. Usually it the lens moves up and down several times, and the CD don't spin up. The display reads "no disc". Once i a while it does find focus and plays prefect. But if I then try to search or stop and play again it starts to search again and then gives up, displaying "no disc". I don't know if there is a focus, servo or electric adjustment problem. Can you help me?