I am running Marlin 1.1.9 on a TAZ 5 with an Aerostruder single head. The toolhead began skipping when trying to extrude a while back. I noticed at that time that the fans were not running for either the heat sink or the blower. I have tested them both with a separate power source and they both work. However they do not run when plugged in. (If I remember correctly, the heatsink should start running once I turn on the printer and the blower should start when the job begins.)
At any rate, what should I start checking to begin solving this?