The type of transistor is not really important, as long as it is PNP (like 8550, data sheet attached) and capable of delivering enough current for motor (1.5A in case of 8550, more than enough).
Sharp picture of top and bottm side of the printerd circuit board can help reverse-engineer the schematic.
(BTW, is it 8550 o5 8050? The other one is NPN, more common in driver circuits like this one.. byt then again, it all depends on the design details).
Is
this the controller?
More
here.
I can't see the voltage regulator on the image... is it below the board?
If regulator is not there by design (to make it cheaper), 12V could have fried the processor (or Zener at the power input, it seems to be there), in which case you will have to try to find hand pad replacement.