Hi, I am a beginner and having trouble (very basic) soldering. I've got my iron on 480deg and I've got a resistor plugged into a practice board where the leads pass through. I am applying the tip of the soldering gun to the resistor leg and hold it there for 4-5 seconds. I then apply the solder to the leg that I've heated. Sadly no solder melts. What am I doing wrong?