How to check regulator:
Attach multi-meter testing pen to both end of regulator, measure 12v while main power supply to MCU board. Replace it if the values lower than 12v.

How to check transistor:
Attach multi-meter’s testing pen to the 1st & 5th and 2nd & 5th pin of transistor, measure the voltage while main power supply to MCU board. Replace it if the values lower than 12v and 5V.

If Transistor works well, replace the 12V Power Transistor (3) at priority, follow by IC Chip (4)