In most cases if the print cooling fan doesn't power on, either the fan itself is broken or there is a wiring issue (fan unplug, fan connectors damaged, etc,) Additionally if the fan is not enabled in the slicer, it may not turn on during a print when expected.
In some cases, the fan output on the board itself can be damaged. This might happen in case of the fan wires being shorted together or other damage to the machine. It is not necessary to replace the controller in this case, as there is a spare fan output on the control board which can be used in place of the original fan output.
See attached pinout image with the correct
output highlighted in yellow.
Move the fan connector from the FAN0 output to the FAN1 output highlighted above. You may need a small screwdriver to push the locking tab of the connector in order to unplug it.
Updating the configuration file
First,
make sure you are on the latest version of firmware. Run the 'M115' in
console. If it reports version is 3.1.1 or higher you are OK, if it is 1.18.x or 1.19.x you will need to update, instructions are in the link for firmware updating above.
Once the firmware version is confirmed,
you will need to edit the /sys/settings/extruders/leftextruder_rightextruder.g (i.e. HFA_HFA.g) file either over the web
interface, or by putting the internal SD card into your computer and
editing it. How to get at this internal SD card is detailed in the firmware update instructions linked above.
On newer firmware (version 2.0 and higher) the M563 settings are the /sys/settings/common_settings.g file, rather than /sys/config.g
Code Screenshot for reference. Ensure "F0:1" is present in both M563 commands Look
for the M563 commands under the left and right extruder sections, and edit
them to match the attached image. You'll want to confirm they have 'F0:1' present in the command, if this isn't present, add it to both M563
commands.
Wrapping up
Re-install micro-SD card, control box cover, and re-apply power. From the Print menu, turn the fan speed to 100% and confirm that the fan runs properly from the new fan output.