Remove the twin wheel cutting plate (A) and the thin shim spacers (B) from the sliding carriage (C) using a 6mm Allen key, slide it off the top end of the slideway carefully.

Then pull the plastic strip (D) away from the top end of the slideway and remove the pulley bracket by taking out the two small screws (E)using a 5mm Allen key.

The next operation is to thread the replacement cord through a long hole in the sliding toggle (F) to make this easier the end of the cord can be stiffened using superglue and then trimmed using the following instructions.  Take a piece of plastic bag large enough to cover the palm of your hand and lay the end 5cm of the replacement cord on the plastic. Place a few drops of superglue along the cord then close your hand and squeeze the cord while pulling it through your palm. Trim the end of the cord at 45 degrees. Please note: care must be taken when using superglue to not get it on your skin.

Next one end of the balance weight cord is fixed to the sliding toggle (F), slide this out of the top of the slideway and remove any remnants of the old cord from the fixing hole. Thread the stiff end of the new cord through the hole (making sure it is threaded in the right direction, down from the top). Tie a knot just above the stiff part of the cord to stop it pulling through the sliding toggle (F) and cut the cord off just below the knot. A few drops of  superglue (follow the manufacturers instructions for use) can be applied to the knot to prevent it coming undone.