Thank you for your answer.
Yes It could be something completely different. The device is control unit for hobby MIG welder.
The control unit is taking care about triac drive (Power regulation for welding transformer), it's taking care about the wire feeder, etc...
The unknown chip U2 is without any text on the package. Maybe some text was there but it was under thick layer of paint and it's gone since I've scratched the paint, only dot at pin 1 is present. I do not think that this chip is ASIC, because if it would be an ASIC, why the vendor has placed J1 header on the PCB. There is no adjusting trimmer on the PCB (e.g. for final setting during manufacturing process) and nothing is connected to this J1 header. Header pins are +5V, GND and two pins are exclusively connected to the U2 to pins 4 and 18. That's why I'm convinced that U2 is an MCU.
I'm familiar with MSP430 and AVR family and Im not aware of a chip with Vcc and GND on pins 7 and 9 (There is no other pin with direct connection to the GND and Vcc) so i went through different MCUs and I found that STM8 is veeery close...Except for pins 5 and 6 which must be AD inputs in my case and there is also no voltage reference on pin 8 in my case... etc...
