How to find a defect in the AIWA CD changer?

Question

Compact disc

In the AIWA NSX-KF7 music center, the CD changer with Audio-CD and Video-CD behaves strangely. Cannot read the first track of a CD-audio disc: the head fumbles at the beginning of the disc, then grabs 1-3 seconds, then goes back. The second track and subsequent reads normally. The head is clean, there are no breakdowns of the mechanisms. I accidentally discovered that if the music center is tilted in any direction by about 15-20 degrees, then the first track immediately starts to read normally . Video-CD is not available now, so I can't say anything about the center's work with them. The center was bought around the end of the 90s, I can’t find a service manual for it. What could be the reasons for this defect?
Head KSS-213B.