If life hands you lemons, you’d better test them to make sure they are lemons.  Here’s a few handy steps for testing the magic smoke containment system of N channel MOSFETs…

1) Measure resistance between source and drain, it should be infinite.

2) Apply a charge between the source and the gate. A DMM on diode mode may source 4 volts.  Some DMMs only source 1.5v and that’s only enough for logic level FETs. Analog multimeters will often source quite a bit more. Batteries are Ok too..

3) Measure resistance between source and drain, it should now be low.

4) You can discharge the gate with your finger to repeat the process.

 As a final test, if the FET has totally wrecked itself, it will conduct between source and gate. If it beeps, it’s headed for the bin…