Is there some trick to tensioning the balance spring on a second hand door?
There are no obvious holes where a locking pin could have been removed and trying to do the job in situ is way beyond my strength.
Unlike a domestic window blind, the shaft has a square section at both ends so you can't just lift one end and wind on some tension. The slats weigh about 75kg so lifting without mechanical aid becomes progressively harder as slats are wound on!
Help!
regards