Replaced the T-Con board today to find exactly the same symptoms, TV reacts in the same manner and the T-Con board buzzes, I find it hard to believe that both T-Con b/d's are faulty with the same fault, possible but highly unlikely.
So, its either the panel, tabs or Main A/V b/d, still believe it to be the Main A/V b/d, would prefer to find the fault and repair at component level but shall keep a look out for a cheap replacement board in the meantime.