If the volume control is scratchy and wave band switch is noisy when rotated, try proprietary switch cleaning aerosol. Maplins probably stock it. Failing this WD40 will work - use sparingly on the switch contacts and inside the volume control assembly, be careful as you can make an oily mess inside otherwise. Note this is internal work, fine if its a battery powered set, make sure set is isolated from mains supply before removing cabinet parts! Shouldn't cost to much to have this fixed if you can't carry out the work yourself.
Mervyn Deeley
November 2007