Looks like the Primary side of most simple Switched Mode Power Supplies and I assume that the required transistor fits on the board in the position marked "U1" - OTOH, doesn't really give any info that would help in choosing a replacement transistor as that would depend on the values of the components around it. And, of course, C3 & C4 should also be replaced as a matter of course (by High temp 105C components!) as well as VDR1.
NB: if not already done, you should check the Primary windings on T2, and whether D1 to D6 D8 are still OK (may be short-circuit). The diodes can be replaced (by same types, especially D5/D6 D7/D8 which may be High Speed types!) but if T2 is damaged then the PSU is probably unrepairable as it was probably a bespoke component that is unavailable (unless you could find another working receiver of the same/similar type!)
