The squirrel fan for the printhead heat sink seems to stay on after printing is finished.
I’m pretty sure it didn’t stay on before, but is there gcode to turn off this fan?
Thx.
Mine has always stayed on when main power was on - since I bought the printer last summer.
Not aware of a way to turn it off.
It should always run.
Huh okay, maybe I mis-remembered. Seems like it should turn off when not printing…but maybe there is a reason for it to be on.
The little blower fan for the heat break is hard-wired to 5v, so no version of the firmware can control it. Instead, it runs anytime the main power is on.
Agreed, it would be nice if it could be turned off. I am not fully versed on the mini-Rambo, but I think it only has 4 mosfet outputs – and those are fully used for the extruder heat, bed heat, print cooling fan, and electronics cooling fan. Firmware control of a 5th item would likely require a different board with more outputs, or some other wizardry (like using io outputs and a relay, perhaps).
I think since you can heat the extruder and not be ‘printing’ something, it would be wise to have it running then to prevent melting the plastic parts attached to it. 
Agreed, but only when the extruder is hot. The desire here is to have the fan turn off when it isn’t needed (and it isn’t needed when the extruder is cool).
Marlin firmware already has support to automatically control a heat break fan based on temperature of the extruder. Of course that isn’t configured for the Mini, and cannot be because the fan isn’t wired to a mosfet output (and as far as I understand, all the mosfet outputs are already used by the extruder, bed, print cooling fan, and electronics fan).
From the Marlin 1.1.0.10 source:
// Extruder cooling fans
// Configure fan pin outputs to automatically turn on/off when the associated
// extruder temperature is above/below EXTRUDER_AUTO_FAN_TEMPERATURE.
// Multiple extruders can be assigned to the same pin in which case
// the fan will turn on when any selected extruder is above the threshold.
#define EXTRUDER_0_AUTO_FAN_PIN -1
#define EXTRUDER_1_AUTO_FAN_PIN -1
#define EXTRUDER_2_AUTO_FAN_PIN -1
#define EXTRUDER_3_AUTO_FAN_PIN -1
#define EXTRUDER_AUTO_FAN_TEMPERATURE 50
#define EXTRUDER_AUTO_FAN_SPEED 255 // == full speed