Hi
Just a thought is the speaker 8 ohm? the output amplifier is the 8 pin ic ( TDA7052A) next to the two white speaker wires. Is this getting hot to the feel?
To test just connect a 9 volt battery to the supply input and the 10k ohm volume control and the speaker. all should be ok. If it is not working, I suggest you contact Peter Skinner at Chalk Garden Rail as he is the LGB repair man for Hobby Co the UK importer.
Alan