No power except on mains after water damage

After the phone was dropped down the loo, my wife towel dried and immediately tried to charge!!!! Not working. I have taken apart, dried in rice for a few days and now I only get the start up sequence with mains power applied despite 100% battery symbol. It instantly goes to 'connect to iTunes' screen. It will only intermittently power up on USB (3 second apple symbol and then off for 5 seconds) and so I cannot connect to iTunes. I have followed the guides and changed the battery and charging block but the symptoms remain the same. There is no other visible damage and so am I looking at a logic board next?