Likely to be a protection relay or similar device that is stuck in the open position so no sound gets though to loudsepeakers.
You need a Service Manual, or at least a circuit diagram to analyse.
As the headphones work, the fault won't be serious, a tech should sort it out fairly easily.
S
Hi
Thanks for your reply, have just got the SM for it, will have a good look when I get home from work.
Cheers
Spike