Fan control with A20T / GT2560 V4
The GT2560 V4 has 4 fan connectors with 3 seperate pwm pins.
J30 is wired to the part cooler and is adjustable. Ok so far.
J31 could be wired to the printhead, but the wire at the connector for the printhead is missing.
J32 and J33 are connected to the same pwm pin. The mainboard/chassis fan is connected to J33 but normally it's not adjustable. So it runs on full speed.
Near J32,J33 I found J34 with a jumper on it. After I removed the jumper the chassis fan stops spinning, but with Vert's Marlin dev firmware it was possible to control it with "fan speed3" option in the lcd controller menu. Marlin 2.0.x has also an option to configure a controller_fan (for example "#define CONTROLLER_FAN_PIN FAN2_PIN" in Vert' firmware) that should spinup the fan, when drivers were activated. But this feature seems currently not to work.
I also connected a test fan to J31. After I added "#define E0_AUTO_FAN_PIN FAN1_PIN" to configuration_adv.h in Vert's Marlin stable build 482 the test fan starts when the extruder (hotend) reaches a temp of 50 °C. Seems to be great to connect the extruder fan to this connector and it only makes noises, when it's really needed.
Is Geeetech planning to make fans easier controlable with a future firmware? I fear not. :/