Zonestar Extruder motor does not work - what can I check?
Good investigation there!  You are almost certainly correct that a driver chip has gone blooey.  Personally I doubt it's worth the effort to locate and repair, rather than buying a new, trustworthy board.  

I recommend this approach because one blown chip may well have caused (or been caused by) unrecognized damage elsewhere, which might then lead to future failures.