Cut a long story short the board was working. However (yes I did mess with it) the small pot on the board was crackling, when turned up/down.
So I removed the board, and had a look at the pot. 1Kohm..tests fine, resoldered it for now, will replace later.
Plugged back in..3x led flashes.. and nothing. Lots of crackling, when I turn the pot, but no actual sound.
I've read through previous posts, with similar symptoms. No definite answers.
So far I have:
Reflowed all the connections, checked any open circuits with the big transistors U12 and U13. All good.
Reseated all chips / ROMS.
Still the board boots correctly. And there is 5vDC on the TP1/2.
I'm kicking myself..WTF was I thinking. Quarantine makes work for idle hands. Plus there are no spare boards. But my board boots correctly!!.
Any ideas..I'm taking a couple of hours out, and try again tomorrow.
Thanks for any help.