Hello Piero,
The advice from Jjh1425 is good advice. The problem you describe is not unknown in Philips transports. It happened to me with an Audio Research CD-2 with the Philips 12.4 transport. I took it to my local AR dealer for service. He said that technically the laser was within official spec's--somewhat marginal--but still within spec's. I told him I wanted a new laser anyway, even thought the machine would play 99% of my CD collection 100% of the time. He installed a new laser and the problem was cured. I think that the player even sounded better on all discs after than; but this could be psychological.
These kinds of problems are very frustrating! Good luck!!