On Monday, August 26, 2019 at 3:11:44 AM UTC-7, wrote:

I have tried searching online, but couldn't find anything that gave me any indication of the specs of the transistor...

piotr and Phil are correct, it's probably a TL431 (or one of the many clones);
to get it to blow up, takes lots of current (and probably another component
was the cause). Install another TL431, another optoisolator (the four-wire
black rectangle), and certainly check out the
diodes (reverse voltage, if the diodes don't block it, could have done in the TL431).

That looks like a single-sided phenolic circuit board; they can get damaged,
so examination for cracks and some care about stress applied when under soldering
heat are in order. The project can benefit from solder-wick and liquid flux.