Hotend heating failure too short before limit I am trying to resolve this for months and have tried almost everything, I guess.

I am using Marlin firmware on a custom extruder with a custom fabricated heating block in which heater and thermistor (Marlin Temp_Sensor 11) are set up perpendicular to each other. Whenever I try to heat it up to 200 degree Celsius, it falls short and fails at around 140 and that too with a very low pace (especially between 100 to 140).

I have already tried PID tuning, ADC values calibration, etc. Also, I have tried varying the values of Watch_Temp_Sensor in Configuration_Adv.h. I don't know what's going wrong.

Can extruder coldend fan have an effect on the heating of thermal block?  I have tried heating the hotend without cooling the coldend, although it takes around 10-12 minutes yet it works perfectly fine then and it reaches to the desired temperature.

The power supply is working fine

P.S. I am not using any kind of pre-built extruder like E3D etc.

This is the setup:



This is the thermistor setup:



This is a view of heater position:
There are many unknowns at this point, you need to work methodically through each stage. You probably also need some test equipment, at least a basic multimeter. Ideally a temperature probe too.

First, check that your power supply can drive the hot-end directly. You already know how long it takes to reach 120°C, so be sure to not let it heat too far beyond this time. This will bypass all of the control logic, and risks overheating your hotend/burning out the heater - but it should be OK if you limit to a few minutes.

Check the temperature reading, and cross check with some PLA or other low melting point filament to see if you actually reach ~180°C. Check the voltage as close to the heating cartridge as you have a connection point. It should be at least 11V (with a 12V PSU). My guess is that you have a bad connection somewhere...

If you observe the hotend getting hot enough to melt plastic, check the thermistor readings. You should see a fairly constant rate of heating well past 200°C. However, I expect this will work fine.

Finally, check the hotend mosfet drive and output as the hotend reaches the target temperature. It should be on, then switching on/off, then off as you pass the target.

If this all looks OK, repeat but with the board in-circuit and controlling the heater. It may be that the mosfet is damaged, or it is not being driven very well - but to progress past that point we need to see voltage readings at various points.