To anybody out there still searching and trying to identify this part.
i have contacted one reputable electronics components seller from aliexpress and i go this response:
As you can clearly read it, the component original part no was ITCHED AND ERASED By formosa the company OEM manufacturer of the subwoofer plate amplifier INTENTIONALLY To prevent anyone from repairing their products if they fail.
SMS5408 Is not the actual part no, there's absolutely no part carries that part no, its just an attempt from formosa company to fool anybody who wishes to repair their unit that there are NO AVAILABLE SPARE PARTS Which is false because its actually available.
i reviewed this YouTube video as well and in the comments, one person mentioned that the part is not MOSFET BUT ACTUALLY AN IGBT !!!!
So the GDS Markings on the board ARE ALSO WRONG AND JUST AN ATTEMPT TO MISLEAD ANY PERSON Who wishes to carry out a repair, i have contacted the person who wrote the comment as well as the video poster but with no replies.
Conclusions: BOTH THE SMS5408 PART NO AND BOARD GDS Markings ARE NOT CORRECT AND INTENTIONALLY IMPLEMENTED THERE TO MISLEAD ANY PERSON AND MAKE THEM GOES IN CIRCLES AND NEVER FIND A SOLUTION.
Bottom line: the board needs to be reversed engineered by someone who have an in depth knowledge of electronics circuits and their design to figure out the characteristics of those parts and figure out a substitute replacement parts which is simply beyond my knowledge.
hopefully someone out there with the initiative and enough solid scientific background can help one day
