Matsui scart problem

[tgb]

Hi,
Can anyone help please. Matsui 1414R tv. When I play a dvd through the scart socket the picture works fine but the sound is from the tuner! Mute works without the scart lead plugged in, but as soon as the lead is plugged in, the sound is whatever channel the tv was on before pressing AV. I've changed leads and I've tried another dvd. The problem is pin 20 of the scart input (sync) which seems to be instructing the processor to select the wrong audio source... any suggestions (or a circuit diagram) are much appreciated.
Best wishes to everyone,
Grahame

Many thanks to everyone who looked at this fault. The problem was a piece of copper bridging two tracks (poorly etched) across the transistor that drives the 'INT' 'EXT' switch in the audio amp.