Print fan RPMS fluctuate
If I go into Settings / Temperature and set Fan speed to 128, then go to Support / Extruder info and check the Print fan RPMS, its jumping around from 3200 to 3600 RPMS. Its doing this on all three MK3s's. Is this normal? I would think PWM would have a little closer tolerance. I'm trying to track down why I get Err: Print fan error's all all three of them at random times on random prints.
The jumping is normal due to how the fan is driven and RPMs are measured.
If your tach wire is intermittent it can cause print fan errors. Try setting the fan to a fixed value and flex varous parts of the yellow print fan wire while watching; if it drops to 0 or another low value then you've found the location of the break.