Microwave - needs repair (TR7)

800W microwave, clock, timer, etc. works, but it is not heating. Apparently, this should be relatively easy to fix for someone who is savvy with electrics (we are not). We have upgraded to another appliance now, but if anyone can make use of it and save it from the tip, please let us know straight away as it'll otherwise go to the tip tomorrow (Sat, 27.08)