strange heat bed temp reading

[sonra]

Hi guys
I use the M2 for long time with Simplify slicer . I don't know but lately I notice that during print cycle the heat bed display reading is not stable and it go up and down from 40-75 degrees Celsius (it is set to 65 ) .The print cycle is OK . What can cause this ?
Regards Doron

[KaiborgStudios]

Can you confirm whether the actual bed temperature is fluctuating? If you have an infrared heat gun, check the temp when it ready particularly low or high, as well as neutral. It could be as simple as a failing thermistor on the heatbed.

[ednisley]

What can cause this ?

A failing thermistor: replace it now!

It could also be an intermittent wiring connection, but my bet is on the thermistor itself.

When the thermistor (or connection) fails with (briefly) a higher resistance than it should be at the correct temperature, the firmware thinks the temperature is too low and turns on the heater, which pushes the temperature higher until the thermistor reports what looks like the proper resistance. When the thermistor un-fails, with the hot end at the higher temperature, the heater turns off and the hot end cools to the correct temperature.

Eventually, the thermistor will fail permanently, so you have advance warning!

[sonra]

Hi
thanks will check it . is the thermistor the same as the one in the print head ?

[sonra]

hi ,
Replaced the the thermistor( the same as in print head ) .look OK now thanks for help
Doron