Use a spudger to disconnect the headphone jack cable from the logic board. You need to gently pry the connector toward (or up, if you like, the connector is like LEGO® building blocks) the front of the iPod until it comes loose from the logic board.

Special hint for the reassembly: Push the connector inside until it is over the corresponding connector of the logic board. Then insert a thin tool over the connector and push it down onto the logic boards connector.