how to fix the sound on my panasonic TX-W28R4DP television?

The TV was working fine, a slight 'pop' occurred & the sound has gone, not even from the headphone socket.

Picture, remote control, all channels, av1, teletext etc. are all OK - just the sound has gone.
I've tried using the internal speakers & external speaker connections. This is on a Panasonic TX-W28R4DP tv. Serial number LB-9252704; euro 4 chassis.

Any help would be useful - circuit diagrams, schematics, which IC's or components to check out, volts or currents to check for