the 370v line you refer to is rectified mains after it has passed through the pfc (power factor correction)circuit, so you know at least mains is reaching the set, after that stage is the 5v standby which provides power for the micro and remote sensor, there are two versions of this psu, one uses a fsd200 and this one is by far the most frequent used.
when this ic faills it usually blasts it apart, the 5v you refer to, is this on the isolated side or some stage on the primary, as i have said, if the 5v line on the secondary is present this means that the remote sensor and s\by led is being fed as is the micro.
we do these all day so know the psu.s pretty well, if the secondary 5v is there try turning the supply on with an external 5v line, the p-on is clearly marked on the board, when you have carried out the checks if i can be of any more help let me know
tony walker
