My Hitachi C28W511N keeps turning off?

I have forwarded this question before, and "cobweb" replied stating that 3 pin voltage regulator on small PCB probably dry jointed. I re-soldered this and for a while the TV was ok. Now it keeps going off again and remains on standby - sometimes difficult to turn on at all and clicks back to standby immediately. Small PCB looks ok, could be another dry joint on main PCB, but where - this is so frustrating, and similar prob to Paul Barrett's also this month.