I'm wondering if there should be pullups/pulldowns for *all* heaters, as well as stepper enables, in front of the tri-state drivers (not just for FET5/6 which are active-high, unlike everything else). Because guess what happens if the Due is not connected, or VCC fails. Yes, everything is turned on, due to pulldown/pullups on the other side of the drivers.
EDIT: yeah pullups won't quite work if VCC is not connected. But I'm still wondering why my FET1-4 turn on when Due is unconnected. My reasoning is if there isn't any voltage on V_GATE there's nothing to turn on the (big IRLB ) FETs... Or maybe it got some voltage from those LEDs in reverse or something.
EDIT: yeah pullups won't quite work if VCC is not connected. But I'm still wondering why my FET1-4 turn on when Due is unconnected. My reasoning is if there isn't any voltage on V_GATE there's nothing to turn on the (big IRLB ) FETs... Or maybe it got some voltage from those LEDs in reverse or something.