FIND A HEAP OF discarded consumer goods and nine times out of ten there will be a microwave oven in there.

Provided it’s free, there are plenty of small but useful components inside a microwave oven that are worth salvaging. However, there’s also a potentially fatal surprise for anyone who delves into the innards of a micro-wave oven without knowing what they’re doing.

So how can you make sure you survive the encounter and what will you find in there that’s useful?

Danger!

Inside a microwave oven is a capacitor that may well be fully charged to well over 2000V. If so, that capacitor has enough stored energy to kill you, so it must be made harmless before you can proceed any further. In addition, there may also be other charged capacitors on the mains input just waiting to deliver a nasty shock.

Once you have connected the Active and Neutral pins of the power plug together (to discharge any capacitor on the mains side), cut the power cord off so the oven cannot possibly be plugged into the mains. This is a very important safety step.

In most ovens, there is a bleed resistor across the high-voltage capacitor to discharge it after the oven is switched off. However, there is no guarantee that this resistor has done its job or is even still intact.

If the bleed resistor has gone open circuit (or if no bleed resistor is present), then the high-voltage capacitor could still easily have several thousand volts on it long after the oven has been switched off and disconnected from the wall socket. What’s more, it can retain this lethal charge for many months.

That means that you have to assume that the capacitor is charged to a lethal voltage and must be safely discharged before you can remove any parts from the oven. You do that by first briefly shorting each capacitor terminal to chassis and then shorting the terminals directly together to make sure – all without touching anything.