temperature fluctuation

What could cause this kind of temperature fluctuation ? Bad thermistor ? Bad connection between thermistor and board ?
Of course the print failed with " Error: MAXTEMP triggered, system stopped! Heater_ID: 0 "

This has started after a pause of a few week of not using the printer...


It's a custom i3 running Marlin on a MKS Gen1.3 with ATC Semitec 104GT-2 thermistor

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Prusa i3 w/ Marlin firmware | Simplify3D | OctoPrint / Nautilus

did you try to run a PID auto tune? are there any fans or ac units close by that could be cooling the thermistor? could be gremlins... look into it and get back to me

i did ran pid tuning . that was when I first installed the heater.
the sudden drop of temperature (20-40C) between 2 consecutive readings can't be caused by a fan (by the way, theres no fan running except the heatsink cooler) )
any other ideas ?


PS checked for gremlins. none found. YET!


UPDATE: strangely, this only happens while printing! I turned on the heater and it stayed at constant temperature without much fluctuation (at least in acceptable <1C tolerance ). what can cause it to fluctuate when it prints.. ?

Edited 1 time(s). Last edit at 09/01/2016 03:56AM by moonshine.

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Prusa i3 w/ Marlin firmware | Simplify3D | OctoPrint / Nautilus

This explains it... The movement of the head during printing would cause the bad connection to give bad readings...




Note: No gremlins were spotted before, during or after the incident.

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Prusa i3 w/ Marlin firmware | Simplify3D | OctoPrint / Nautilus