Lenovo Yoga 530-14ikb motherboard does not start

[mux18955]

I'll tell you right away, I don't understand much about electrical engineering. I have this laptop, the symptoms are as follows: when I press the power button it lights up for about 5 seconds and then goes out. The fans do not spin, there is no effect at all.
Here is what diagnostics I was able to run:

1) The motherboard sees the battery (the button lights up white if it is connected and red if it is not, as if it is almost discharged).
2) The charging LED is also on if the battery and power supply are connected (without the battery it just flashes quickly and goes out when the power supply is connected).
3) Power on USB ports, including Type-c (the phone charges with "fast charging").
4) When pressing the power button, the heatsink above the processor does not get hot

The most interesting thing is that I've had this before, a couple years ago I already changed the RAM and SSD in it, after that I had exactly the same symptoms. The laptop was without battery for a year, after that I took it apart to take pictures of the motherboard, tried to turn it on again and didn't understand how it turned on. At that point I was literally just plugging and unplugging the PSU plug. This time that trick doesn't work.
Yes, the response to the "reset" button (or whatever it's called on Lenovo?) is the same as to the power button. I also looked around, and it seems that there is no CMOS battery (not designed in principle?).

Thanks for any help

[mon2]

Try the recommended answer posted here:

My computer won't turn on - Lenovo IdeaPad 530S-14IKB - iFixit

[mux18955]

Try the recommended answer posted here:

My computer won't turn on - Lenovo IdeaPad 530S-14IKB - iFixit

Yes, I tried that too, unfortunately the result is the same. The only thing I remember and what I'm almost (!) sure of is that the last time it turned on after such an idle time I didn't touch the power button at all....
In fact, I would have thrown this laptop into a long box if there had not already been such a precedent with revival. Maybe there is some emergency (?) startup mode, maybe there is some way to start the motherboard without the power button.
It may be possible to short some pins on the cable from the power button board to the motherboard, but I have not been able to find the pinout of the connector of this cable. It is quite possible that the cable itself is just bent or broken.....

[mcplslg123]

Is the power button on Keyboard itself?
Usually there is NOVO button on motherboard which you can try to power it on after disconnecting the KBD.

[mux18955]

Is the power button on Keyboard itself?
Usually there is NOVO button on motherboard which you can try to power it on after disconnecting the KBD.

No, the power button as well as the NOVO button are on the side, on a separate board connected by a daisy chain (see pic). The response to both buttons is the same - the power button lights up for 5 seconds and then goes of

[mux18955]

Just now with no hope it stood just plugged power supply in for a couple hours. With nothing to do, I started plugging and unplugging the power supply again and it turned on again! I unplugged it to insert the battery and it died again (same symptoms). Still waiting for help...

[mon2]

Disconnect the battery and test it again with only the power supply.

[mux18955]

Disconnect the battery and test it again with only the power supply.

No, I tried the same methods without the battery, but it's the same thing. I guess it happens once in 100 times. Is it possible that there are no contacts on the motherboard itself that can be shorted?... Or on the cable from the board with the power button?...