denon dcd 1500 II tracking problem

[iapx8088]

I got a denon dcd-1500 II and I fixed it some time ago (bad belt on the drawer). I also removed my mute transistors (see http://ezralabs.esaurito.net/personal/denon/ )
I have this problem. The reader reads fine almost everything, but it fails with some cd-r. This would bother me but the catch is it can't read no longer some old cds.I can recall perfectly it used to read perfectly. It seems to me that when this happen, a weird noise comes from inside, as the cd would spin on the wrong way and then again on the wrong way. In the end it does not discover the cd and just sits there or search endlessy.
I wonder about the laser but I don't think so because it reads almost everything. The cd it can't read are not scratched or damaged, and play fine in other readers.
I went to repairfaq.org and read about this problem, but I don't have any oscilloscope at hand.
Please help, it sounds fine, I'm going to change the opamps and it would be bad to scrap it. I'm accustomed to it.
The service manual would help? Anyone has it?
thanks.

[iapx8088]

Don't care anymore, right yesterday the laser died of natural death.
Moderator, you can scrap this thread if you need.
What the hell.
No red spot in the lens, the lens comes up and then down and no cd spinning. What the hell.