Temperature is not constant when I printing. Ender 3

[Pankla]

Hello my problem is when I click preheat to PLA and printer heat up to the right temperature, temperature is constant and stable but when I start printing immmdiately temperature jumps up and down and is not constant. I buy new thermistor and replace but this not fix my problem so I decide to post this because I don't have any other idea to solve this problem. Do you have any ideas to help me?Link to video show the problem: https://streamable.com/ff2ttw

[Roberts_Clif]

There could be several problems.

New Firmware configuration.
Print speed to fast causing hot end to cool.
Bad hot end heater.
Loose hot end wires.
Power wires running to the controller will not handle the load.


I would start with measuring the Supply voltage on the controller board to see if is varies during print.
If it varies much replace supply power cabling to controller board with larger wire.

Once to can guarantee the voltage is stable all the way to the hot end then you may have a bad hot end heater.

If you have recently changed your firmware you may want to check all you configurations are correct.