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I think I tested it last time with the speaker disconnected and it still blew the fuse.
It doesn't matter if the speaker is disconnected, if Q10 and Q11 are blown short it will still blow the fuse. Put the meter on diode check and check the output ahead of the relay - L1 and L2 will guide you to that junction.
Not saying you are wrong or anything but are you sure it's a MOSFET?
Check that 100V cap at top left of the picture. It looks decidedly cooked (or perhaps that goo is just hot-melt glue?). The transformer seems to have been running hot too, judging by the discolouration of the pcb.
It looks like just glue.
Was the bridge rectifer OK then?.