My integrated freezer APP 6403 ?

My integrated freezer has now given up altogether after bleeping continually over recent weeks. I have seen loads of similar comments about this particular freezer, it is only 3 years old, but of course is out of warrantee. Can anyone tell me how easy it is to repair, I have seen comments about replacing the thermostat or some say the PCB. How will I know which needs replacing? any advice will be gratefully received.