A mobile radiography system includes a wheeled transport frame and a vertical column mounted on the transport frame. A boom is attached to the vertical column and to an x-ray tube head. A boom carriage allows movement of the boom along a track in the vertical column and includes a magnetic mechanism to lock the boom in the track at a desired height. An electromagnetic coil in the boom carriage is configured to disable the magnetic lock mechanism to allow vertical movement of the boom along the track.