In the process of doing a makeover in the darkroom, so have my an opportunity to pull the enlargers apart and do some maintainance. General cleaning and lubrication of the moving parts is complete, but I find I need to adjust the locking mechanism on the right hand side of the column. Looking under the covers, I see a chain & cog and a sliding plate for the lock.. However, I see no obvious way of adjusting the lock to prevent the head shooting up on the spring when the lamp housing is removed. Any advice/tips on tightening things up ?