may a defective side fan be the issue?

[aag 6]

I am getting very frequent tPLA underextrusion on my S5, resulting in halted prints (if the flow sensor is on) or ruined print (if the flow sensor is off). I have replaced both the prinhead and the bowden tube, and I have cleaned the feeder many times. None of this has resolved the issue.

Now I have noticed that the part of the filament entering the upper part of the printhead has an increased diameter, suggesting that it was partially molten. I think that this may indicate that the temperature creeps up from the nozzle to the upper metal tube. If true, this might indicate that the side fan is not working. But it's difficult to see the fins of the side fan, even with a flashlight. Is there a way to test the functionality of the side fans?

 

 

 

Edited August 29, 2020 by aag

[UlrichC-DE 115]

I think the front fan is responsible for this. The side fans are for cooling the workpiece.

[purplehobbies 0]

I am seeing the exact same thing on an Ultimaker 3. It was printing beautifully and then suddenly started jamming. I did all the same thing you listed, new tubes, new print core, cleaned the feeder multiple times only to have it repeatedly fail. Eventually I noticed the same thickness of the filament as your photo. I just logged in to see if there was a suggested solution for this.  I’m going to replace the front fan and will update after testing. 

[aag 6]

In my case it turns out it was a failing front fan. It was still revolving, but at a lower speed insufficient to cool the printheads.

[Smithy 1,146]

Thanks for the feedback!

Yes the front fan is very important to cool the upper part of the printcore.

[SandervG 1,522]

Agreed! Some little strings of filament can get caught up in there and make it stop spinning, or spin too slow. It is also possible that by an unfortunate event that the cables got pinched somewhere. But usually it is some debris in between the blades.