How can I fix my Yamaha DVD player DVD-S520?

The DVD player reads DVD's ~95% of the time OK, however when playing a commercial music CD, the player will play for ~ 20 seconds or so, then it begins to 'hunt' and stop playing the disc.

Its as if you can hear the laser joggling back and forward as if unable to stay in the 'track/grove'.

Play is disrupted for up to some minutes and sometimes it will not restart at all, ejecting the disk as it was not able to read it at all.