Sony STRDB 1080 problem - Video but no sound,says "PROTECTED"
 

hi all,
my friend's sony strdb 1080 (which he's had for about 2 1/2 years) was
working perfectly one night,switched it on the next day and has no sound at
all. video still comes through fine.
the display says "PROTECTED"
we've opened it up and everything looks fine,fuses ok etc.
have also tried holding the power button ,which resets it,no difference at
all.
any help much appreciated,
cheers,
col