What you need to do is a service wash.
To do this set it to the hottest wash which is about 90 deg and set it going with nothing in.
Just add a small amount of soap powder and let it just boil itself clean.
Now you may need to do a few of these say 4 a week for 2 weeks and this will clean the inside of the drum as you can get a build up of muck and undissolved soap powder.
It may take a few 90 deg washes to clean it but the smell will go and the washing should be back to normal.
If you need anymore info just get back to me.