LG Gram 17 (17Z90N-R) ADVANCED troubleshooting Power On Self-Test (POST)

[mm1nd]

My LG Gram 17 (LG GRAM 17Z90N-R 17Z90N-R.AAC8U1 i7-1065G7 CPU + 8GB Motherboard EAX68997002) does not seem to even get to the point to try to boot from media (the nvme SSD is fine, I verified it on a separate computer) or turn on the display.

I have tried basic troubleshooting steps, remove the battery, disconnect the display, remove the RAM card, connect an external HDMI display. The behavior is always the same, the laptop turns on, shows the keyboard backlight, starts the fan, then it turns off the fan/light briefly, it does this sequence multiple times, let's say 6-7 times. Eventually the fan keeps running with the backlight of the keyboard off.

So it looks like the motherboard is at fault but unfortunately, it is not easy to find one as it is a relatively old laptop and ebay people will not ship to my location.

I wonder if the on-board RAM may be the problem, or may be a component of the power supply,... something that I may be able to replace. So I have some questions:

1. Where can I find a repair/maintenance manual for this laptop?
2. Is the POST test failing? Is there any way to know what fails during the POST test? Does the keyboard backlight sequence represents the error code? Any serial or board debugging option?
3. If I unsolder the on-board RAM (how do you recommend to do this? Is there any video that shows the process for a LG Gram laptop?), and I use only the RAM card, will it work (assuming the on-board RAM was the issue), or does it always need RAM in the on-board bank? Is there a way to make this test without removing the on-board RAM (micro-switch or similar).

Thanks in advance for any pointers.