Daewoo KOC1B0K

Question

We have a Daewoo KOC1B0K and when it is operating everything works fine except it doesn't actually microwave anything at all. The clock, turntable, timer etc all work but it doesn't cook. A faulty Magnetron has been suggested but we'd like to know if anything else could be the problem. If it is the magnetron is it easy to replace oneself or should a professional be employed?

Thanks