Power supply NTC BLOWN!

[Nicko']

I have a parwell tig welder which I acquired second hand, all was going well then the welder just stopped, I traced the problem to the power supply and the NTC20D-11 HAD BLOWN UP! I bought some new ones but they also exploded on power being applied taking the 3A fuse each time even with no load connected, any ideas why? It's a single phase welder, and I believe this is the switching power supply for the controls,

 

[Bluejets]

Likely the switcher ic or the switching mosfets.