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 motor, which seems to work continuously. Beoworld member, Kevinoils, helped me a lot by suggesting to loosen the little black screw under the tonearm and moving sideways the metal plate just in front of it (adjustement of diaphragm  page 3-5 of the service manual). Things have improved and the tonearm skates over the record more slowly, but since I did it by chance, still I haven't achieved to keep it completely stable.  If someone can provide a detailed description of how that screw near the diaphragm affects both the tonearm to remain parallel with the lamp arm, as well as the servo motor to rotate in a more controlled manner, it will help me to do more accurate adjustments.  Besides should I make these adjustments with the platter and the belt on or off?

 

I have the same problem now and then with a BG4002. A gentle push to the right on the tonearm when in raised position solves the problem for me. However, I do not use the deck on a regular basis due to some ground noise not yet solved.

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.