I can't get part cooler fan to work.MKS GEN L V1.1 / Marlin (2 replies)

Hello my first post here so be gentle!

I have built a FLSun I3 plus and, with some modifications, it works OK. I added a part cooling fan and plugged it in to the "Fan" / "D9" socket (= arduino D9 pin) and try as I might I can't get the fan to move.

I have tried:

Another fan.

changing this line in marlin/Configuration_adv.h
#define FANMUX0_PIN 9

Any ideas?

I am assuming using the touchscreen controller to set the fan to a non zero speed should work anytime. I have printed a PLA object to test too.

FYI:
The supplied hardware loaded with recent Marlin and configuration seems OK apart from this issue.
I added a simple "discount" controller as well as the touchscreen.
Control arduino mega RAMPS board is a MKS GEN L V1.1