Prusa i3 does not turn on both heaters, what should I do?

Question

Iron

Collected from a set of prusa i3 Chinese board mks-z2 gen1.2; a problem came out - it does not turn on both heaters at the same time (only turns on the extruder or the substrate catches up with it to the max temperature and turns off).
The behavior with both the memory card and the computer is identical, the power supply is normal. where to dig?

Answer 1

I asked myself and I will answer - replacing the firmware with the firmware helped