How can I fix my on/off switch on my post drill?

I have a Performance Power Tools bench post drill. The on/off safety switch does not function properly. The drill will not operate unless the on button is pressed on and held on. I have managed to get the drill working by holding the on button depressed using a clamp fixed across the body of the drill. I feed power to the drill through an RCD unit and the test button on the RCD unit acts as an emergency off switch. Is it possible to take the switch apart and repair it. It sounds like a solenoid switch as it buzzes when the on button is released slightly.