LG 50PC1 -psu board blowing fets

[cornboats]

I'm trying to fault find down to component level on an LG 50PC1 JO12B power board.
The fuse blows on the board and also trips the house breaker on start up. I've removed 2 banks of fet's and changed 1 fet which had blown. Refitted and tested but now all fets and in 1 bank have blown. I've tested all major components around the fets on the board without finding any faulty.
I've connected to a series lamp test before connecting to mains on both occasions and the lamps come on and off with the relay operation exactly like a working psu.
Any help or advice would be much appreciated.