MOSFET switch is leaking current when off

Question

I have an N-Channel MOSFET that I'm using as a switch, and after wiring 20 identical circuits, I'm finding that 3 of them seem to leaking current when switched to off.

The MOSFET I'm using is from sparkfun:

https://www.sparkfun.com/products/10213

I am using the switch to light an LED.

Gate - 3.3v GPIO pin of Raspberry pi

Drain - Negative leg of LED

Source - GND

I'm using a 10k resistor as a pull down resistor, which is wired up connecting the Gate to the Source pin on the MOSFET

^{simulate this circuit – Schematic created using CircuitLab}

For some unknown reason, a small amount of these circuits will have flickering LED's when the GPIO pin should is switched off. Does anyone have any thoughts what might be causing this? Or any thoughts on ways to test the circuit?

Answer 1

I'm going to assume that your schematic ought to look like this

^{simulate this circuit – Schematic created using CircuitLab}

Testing is simple: short out R1 with a jumper or even just a length of wire. If the flickering stops and the light goes out, you know the gate drive is not zero, and the flickering is "correct" in terms of the input signal. Otherwise, your FET is bad.