Check soldering...
I solved the problem with the screen. Now I'm trying to calibrate everything using T12 tip (chinese one). The handle has an NTC build in, and it is enabled in the menu. The firmware is showing accurate ambient temperature in the upper right corner.
I started in Calibration->Settings. Set the Zero set (when the tip was cold), Cal 250°C, and stuck at 400°C.
Before the tip reaches 400°C (probably around 360°), the firmware aborts the operation with the ERROR DETECTED message.
I'm measuring the tip with a multimeter with a thermocouple.
Currently I have the following settings:
Zero set 612
Cal 250°C 2360
Cal 400°C 3960Maybe the voltage offset of the amplifier is too big. It is unknown 621K amplifier.