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Ultimaker original showing max temp error when fan is on

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had the same proble half a year ago. As you said, the fan could be responsible for this. It´s using PWM for speed control and when not running at full speed a lot of pulses are being sent through its wire. Neither the fan cable nor the thermocouple cable is shielded and the thermocouple is very prone to interference. So the fan causes wrong temperature readings. Easiest way to avoid this is to either turn the fan completely on or off, but nothing in between. The better way is to separate these two cables from one another. That should help.




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You should also try twist the leads for the fan.

Alternately, if you can find a large ceramic or otherwise non-polarized capacitor, soldering it across the fan output on the main board might help. I did this mod and it seem to help but haven't had time to look at the PWM on an o-scope to see if it changes the PWM rise/fall time. The cap in theory should slow the rise/fall time. The faster the rise/fall time, the high the frequencies generated and the more likely they will interfere with the tc amp.


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Well i played about with the fan wires and moved them away from the yellow red wires of the thermo, kinda did something, now i don't get the max temp error with the fan on, but the temp does fluctuate wildly between 220 and 239.

It's definitely the fan as with the fan turned off i get no issues.

Also normally i do run the fan at about 60-90 rather than full blast.

It's just weird how its started to do this problem now, after 3+ months of printing fine. I'll investigate the main board next.

Thanks for your help


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