I purchased an O gauge Lionel train set from a neighbor.  It came with several engines.  They transformer stopped working and I replace it with Lionel ZW 275 Watts Multi Control Trainmaster Transformer 115 Volts AC Postwar.  However when I hooked everything up to it switches on and off.  It is like you can hear it switch on and off when the levers are engaged.  Can someone explain what is happening? Also,  does anyone know about these transformers and can provide and basic instructions on how it woks?