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Heated Bed Temp fluctuates

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on my UM3 when I printing at temperatures of the Heated Bed more than 60 degrees, I have an oscillation of the temperature about to 5 degrees in a short time (about 1 second).
The oscillation occurs only during the printing of certain parts such as external walls or when changes of direction.

I checked the resistance of the printing bed like this guide:
and they seem correct I have no other ideas on what to check.

Thnaks for your help.




Video: BedTemp.zip

Edited by Gio26

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I think oscillation is normal on the heat bed, because there is only on/off, so in the software there is a threshold and if the temp is under this threshold, bed will be heated again for some seconds or until the temp is again higher than another threshold. So this "flapping" is more less normal in my opinion.


But do you have problems with this flapping? Objects don't stick to the bed or something like that?

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Hi ?

ahh ok, no but now I have checked your video.

Hmm, yes looks a little bit strange, I think mine is more stable. But I have no idea how to solve it. I think the temp sensor of the heat bed is "build in" the heat bed. You can only check if the cable is connected well to the board.

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It's impossible for the bed to heat or cool that fast (3 degrees in 1/4 second).  It can't even heat or cool 1 degree in 2 seconds.


It's a sensor error.  I don't know if there is electrical interference or a loose wire.  I'd give a gentle tug to the heater sensor wires both at the heated bed and at the circuit board.  It's more likely at the heated bed.  I would loosen the connector and remove and then re-insert the 2 sensor wires.  Also have the printer on, look at the bed temperature, and while looking at it, push on the connector with at least 1kg force in every direction to see if there is something loose.  It could easily be a bad solder connection under the screw-block where the wires go into the heated bed.  That was the problem with my UM2 (almost exact same design) - the solder joint wasn't good.  I had to reheat it with a soldering iron (this was years ago - it's been fine since).


I don't think it's serious since it seems to be stable enough to keep the bed at a constant temperature but I'd try to fix it anyway.

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