[Richard L]

The most obvious cause of a blown transistor is a short circuit. Other possibility is static electricity.

The transistor used is quite common, made by STMicroelectronics. STN3NF06L. It is good up to 4A. Logic level gate drive. You should not try to put a more powerful device in there. The next short-circuit means a burn out circuit board, not that easy to repair.

Here is the specification:

- Device name: STN3NF06L
- Vdss....... 60V (minimum)
- Id ............. 4A (minimum)
- Vgs(th) ............ 5V logic level
- Device outline package .............SOT-223
- Rds < 0.1 ohm.

You can search google for availability in Russia.