Thank you djram also check the little black screw under the tonearm. Loosening or tightening it affects the way the motor rotates, which causes the tonearm to slide arbitrarilly over the record.

I have recently purchased an old beogram 4002. All the controls of the turntable seem to function well, except from the tonearm. As soon as it lowers on the record, it starts to skate all the way towards the end of the record (probably destroyng both the record and stylus), and then returns to its initial position. This is also associated with the servo