Take off the platter, cartidge and counter-weight.
There are six screws on the back that hold the lid on. Make sure you only undo the three that are not holding the torsion wire!
Once you have the lid off, you can then invert the Beogram.
It might be an idea to arrange some books or something to stand it on without the tone arm holding the weight.
There should be two screws that hold the plastic base on. These screws are captivated so they don't come all the way out (you won't be able to lose these)
Once you have the base off you should see all the workings>The problem lies in a little brass pin which is in a brass sleeve.
Dillen (Martin) has kindly posted a picture of the offending pin here