CD723 transport problem

I have a modded CD723 that shows a strange behaviour.
It worked with no problems until yesterday but then it stopped reading CDs.

I thought it was a problem related to the clock (I use a Tent XO) but clock signal is present.

The problem is that the laser head keeps moving towards the outside of the disk.
When I insert a disk and close the tray the head makes all the run to the centre, the disk tries to start spinning and then it moves again towards the outside, and when it reaches the mechanical limit I hear the clicks of the gear engaging-disengaging. At about half-run the disk tries to start spinning again.

Wht could cause such behaviour?


I ran the test program as described in the service manual and the result was "FOCUS ERROR".

However the most evident thing I see is the slide that moves slowly outwards. It looks like a matter of offset, since I can make the slide move in both directions using the test commands described in the service manuals.
The movement is faster going outwards and this confirms the offset theory....

Any hints?