Ender 3 S1 Pro - Nozzle temperature fluctuation after FW upgrade

[mentos]

Hi guys! I bought an used Creality Ender 3 S1 Pro recently. Everything was fine, I have printed some projects without any problems. I noticed that the Y-axis is very hot so I decided to check the currents of stepper mottors. The currents were correct and I didn't change it. Taking the opportunity that the cover was removed I checked the main control chip version (401) and performed firmware upgrade to the newest one - V2.0.8.28F4_F401. After that the nozzle temperature is fluctuating. I have tried to solve it in different ways but without success.

What is the problem? The nozzle temperature fluctuates. If I set the temperature to the 200C then it goes to the 205, drops to 195 and stabilize about 200 ± 1-2C. The fluctuation occurs everytime when the temperature is changed. Before I printed with 205C for the first layer and 200 for next ones. If I set the lower temperature then fluctuation is even higher - for the 100C it goes 113C.

What solutions I tried already 1) Tuning the PID again - using both the Autotune function on the display and by Pronsole terminal 2) Disassembled and cleaned the extruder parts 3) Downgrading the firmware to V2.0.8.26 and V2.0.8.24 - it was the previous version which has worked 4) Changed the hotend to the new, original one

Notes: -Heatbed temperature is fine -Both heatbed and nozzle temperature show the same values - my room temperature -Used different SD cards - 2GB and 16GB formatted to the 8GB. FAT32, 4096 bytes.

I don't know if the problem is caused by the checking currents or updating firmware. Do you have any ideas what more can I do without changing a motherboard? Thanks in advance. motherboard.jpg PIDautotune.jpg info.jpg

[mentos]

Solved! I had to add a thermal paste onto the heater and heat break and tune PID once again.