Philips 712 hw problem

Hello,
I have a problem with Philips DVD-712. Few months ago it started to making a strange sound when powering up. It sounds like a loud zipper. Sometimes it ejects media and displays “Blocked”.
I found that laser carrier quickly moves to the outer edge of media but it doesn’t stop immediately - tooth-wheel rearranges.

I want to find where the problem is (why it doesn’t stop), so my question is: how player knows that the carrier is at the edge? Have it some sensors? I didn’t find any.

I think it slowly dying. I need to sustain it till february when I want to buy a new player.
Thanks.

Rado.