Well, we had another look at this today. Following your suggestion, Downunder, we connected a monitor. Not possible to see the MENU screen, but good sound and video output to the monitor from a DVD input to the Sony.
To my surprise, when I change "Source", with an aerial connected, the set was fully tuned in. (Here on this small island there a number of relay transmitters, plus N Ireland which I receive, plus Border). Usually I need to tune in, impossible without a visible menu, but not today!
I checked voltages up to the Tcon board, and there were at least five +5v pins, but no +12V. The manual actually shows a +12v source, but it is "greyed out", and marked NC.
It begins to look as if it is a faulty Tcon board, but do I spend money on it, or just scrap it?
The board carries ID mark 320WSC4LV1.1. Prodding and poking achieves nothing.
Les.