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FAN0 inverted PWM?

Posted by stan78 
FAN0 inverted PWM?
July 21, 2019 04:28AM
Hey guys,
my Anycubic I3 Mega is acting a bit weird. A M106 S0 or M107 spins the fan up to 100% whereas M106 S255 makes it run at about 10%. There seems to be some kind of inverted PWM signal. It also won't turn off completely.

Could this be firmware related? I tried Marlin 1.1.9 and now 2.0 bet - makes no difference.
I tried to find something in the source code but couldn't find anything useful.

br st

Edited 1 time(s). Last edit at 07/21/2019 09:25AM by stan78.
Re: FAN0 inverted PWM?
July 21, 2019 07:46AM
It sounds like a defective mosfet, experiencing a Avalanche failure.
This is where the mosfet is partially shorted you will get full power and when the avalanche occurs you would get a crowbar effect giving you nothing or maybe the 10% fan.

The problem with a failure in this type is that, once it occurs, there is a high risk of a chain reaction which could disintegrate the MOSFET an probably blowing other devices to boot.
So it’s of extremely importance to test the mosfet for this defect and replace as necessary.

Using stranded mosfet tests



Electronics Technician / Computer Programmer
Re: FAN0 inverted PWM?
July 21, 2019 08:48AM
Wow, you both did great. Stan for describing the effect really well by trying out the fan settings and Cliff by sharing this really good knowledge. Thanks, I'll try to remember this as well in case I ever come across an error like this.

Re: FAN0 inverted PWM?
July 21, 2019 09:51AM
Yeah, thank you very much for this detailed and probably correct information.
The Trigorilla boards seem to have very bad transistors for the fans. They break easily, allegedly.
On the i3 Mega there is a spare „heater 1“ port with pin D45 that is connected to a mosfet. So I put my fan0 cable to this port and changed the fan0 pin from 9 to 45 in the marlin source code.
Now the part cooling fan is behaving correctly again!
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