Notebook ASUS K73SD does not turn off and does not fall asleep. How to fix?

Question

Do it yourself

Hardware problem. Most likely from the old motherboard.
Shutting down any system (not just Windows) does not turn off the power.
Sleep mode doesn't work either.
The power is turned off only by long pressing the Power button.
Doesn't crash while working. Doesn't freeze. Doesn't overheat. In general, there are no complaints in the process of work.
A few years ago I changed the processor from some kind of Quad Core to an i5 and after that there were no problems for several years.
Everything worked great. That is, for me there is no problem disassembling and reassembling everything. There is no only equipment for soldering SMD elements. Most likely, the capacitors are larger, and if they are suspected, I can replace them myself.
The motherboard on Aliexpress costs from 50 to 100 dollars. I'm not sure what is required to buy. Yes, and after the replacement, there will be problems with the Windows license, I think.
Can you please tell me where to look for the circuit diagram of the motherboard and what exactly needs to be checked?
My opinion is that some capacitors have dried out from old age (or were defective)
and the shutdown signal does not go to the power circuit.

Answer 1

It's worth updating the bios. Also, I suggest trying first without hdd, floppy drive and wifi module to check shutdown - just turn it off by booting from livecd. If there are problems then, then the mother is to blame. But this is strange, because bios is responsible for shutting down first, and then hardware.