I am attempting to change the power cord on a TW transformer.  To get to the terminals I will have to remove a bracket above it which requires disconnecting a couple of wires.  I first tried to heat the solder with a pen and then a Weller 8200  100-140 watt gun.  I still have not melted the solder to break the connection.  How much power does it take?  The tip on the gun has been cleaned and re-tinned for proper heat transfer. I get a little smoke but, no melting.  Do I need more power? Thanks!