My technics sl-p770 doesn?t recognize the loaded CD.A cd is alway spin but not any track in audio cd.

Thanks robcal99 I try clean cd lens but still not detect cd.I use many original cds audio and measuring laser ohm with multimeter got a value R = 4.7K ohm resulting cd spin for a while and then stop then I try tweak laser to 3.4K ohm after that cd is always spin but can't still detect any track !!! :( Thanks robcal99 I try clean cd lens but still not detect cd.I use many original cds audio and measuring laser ohm with multimeter got a value R = 4.7K ohm resulting cd spin for a while and then stop then I try tweak laser to 3.4K ohm after that cd is always spin but can't still detect any track !!! :(