Question Beelink Mini S N5095 with black screen only after restart

[LABenedetti]

I have a very peculiar problem that I can't seem to solve :
Everything works perfectly (with Windows11 or Linux), except when I try to restart it or switch it on before it has completely cooled down, which usually takes about 5-10 minutes.
If I try to restart before that time, it lights up the blue power LED, spins the cooling fan, but goes black.
If I don't switch it off, it stays in this state permanently.
And when it's like this I can't switch it off using the power button: it switches off the blue LED, stops the fan and seconds later switches the LED back on and starts the fan, but with a black screen. Then all I have to do is unplug it and wait for it to cool down. Then it restarts normally.

What I've already done:

- Changed the thermal paste on the processor (which wasn't old)
- Cleaned the RAM contacts
- Tested the RAM with MemTest (2 and a half hours of testing! )
- I removed the glue residue left by the backup battery that was attached to the motherboard (I saw on the internet that this could be interfering)
- I checked the voltage of the backup battery (OK)
- I removed it from the mini-cabinet and thoroughly sanitised the motherboard with isopropyl alcohol and a lot of brushing
- I checked the BIOS settings and turned them back to "Default"
- I reset the BIOS using the CMOS reset button (I held it for 10 seconds without power).
- Tried another monitor
- Changed the HDMI cable
- Tried booting with ethernet on RJ45, without connecting peripherals (keyboard, mouse)

What I haven't done yet but think I can do:

- Reinstall the BIOS?
- Reflow the processor?
- Check the motherboard capacitors (this will be a bit difficult as the board will have cooled down by the time I remove it).

But I'd be very grateful if anyone could give me some advice.

 

[LABenedetti]

As everything suggests that the problem is related to the temperature of the cpu or gpu, I decided to experiment.
I improvised by fitting an extra fan blowing air into the unit and sealing the inlets to force the air through the cpu/gpu vent.
As a result, I managed to bring the working temperature, which I'm monitoring via the Core Temp application, down from 60 to around 43 degrees Celsius.
But even so, the only change has been to shorten the time it takes for it to restart giving video. No restart was possible.
It continues to behave in the same way: the fan turns on, the blue LED lights up but the video doesn't come up.
That's when you unplug it.
But now, with the temperature lower, it's almost immediately giving video and switching on normally via the button. I only need a few seconds when the unit is unplugged.

 

[LABenedetti]

I don’t believe it’s a software or driver issue.
I also installed some Linux distros to see if it changed the behavior.
I installed Lubuntu, Linux Mint, MX Linux and the behavior is the same.
Everything points to a hardware (or BIOS?) issue, especially because when the CPU cools down, the boot is normal.
My suspicions continue to be BGA solder on the CPU/GPU, capacitors (or some other component) with values altered by the temperature or some temperature sensor (on the CPU?) providing incorrect readings at boot. I’ve been monitoring it during operation and the readings are normal.
Is there anyone who’s an expert in hardware who can give their opinion?