Following the example by lady ada here: RGB LED strip tutorial
Using the STP16NF06 as suggested, wired properly, with a TLC 5940 driving them commanded by an arduino, nothing happens unless I hold the PCB in my hands. simply touching the pins of the mosfets, while a fade is running, turns them on until the fade completes (I can let go as soon as everything lights up). The RGB LED's stay dark until I touch the mosfets with dry, bare hands again. NOTE, I did not install the 10k resistors (yet) that I have seen in other depictions, but aren't those to make the mosfets turn back off? My current limiting resistor (IREF) on the TLC5940 is a 2.2k.
I think he did the equivalent, at least he acknowledges that the LED's turn on via the Mosfet's. I think the issue here isn't turning on the mosfet's but what is turning the mosfets on. I also think that without an accurate drawing there is little possible here except conjecture. The interesting point is this
(I can let go as soon as everything lights up)
as it indicates that most of his wiring is ok as it works... sort of and I wonder if the TLC5490 is wired properly as it is the component we know the least about from his sketch/schematic. {Edit: I do think that Grumpy Mike hit the issue dead on as it does sound like an open ground between the Arduino and the TLC5490's.}
Bob