Acer Helios 500 (PH517-51) - unexpected reboots when laptop is warm (cold solder joint issue?)

[Mirenia]

Hi everyone,

got an Acer Helios 500 Laptop (PH517-51) for diagnosing with a strange issue:

The laptop runs for a while (1-2 hours, sometimes less) and then suddenly shuts completely off, like someone pulled the power cord and restarts immediately after on its own.
If this happened once, then the laptop only runs for a few minutes until restart.
This happens regardless while staying in windows or uefi or in a linux environment.

At first I thought of a normal overheating issue, but as I monitored temps with HWInfo64, nothing seems very hot.
Only PCH temperature is a bit higher than the other temps (60-70C) but from what I read online, this seems normal for this model.
There's no bluescreen or helpful error codes in the windows event viewer.

I opened it and cleaned the really dirty fans, repasted everything and put it back together but the issue remains.

My guess is some kind of cold solder joints or a contact problem, which occurs, when the mainboard runs warm.
But I honestly don't know where I should start diagnosing or how I can isolate the error, because the shutdown and restart happens unexpected and fast.

I have moderate knowledge with diagnosing motherboards and good knowledge with electronics, circuits and soldering.
For example checking power rails or components like resistors, caps and stuff with a multimeter.

Do you guys have some advice for me, please?
Or some guess what could lead to this issue?

[Mirenia]

I think I found the culprid.
CMOS battery drops voltage. After a night without power and main battery it only has 0.2V out of 3V left.

I'll change it and hopefully the reboots are gone then

[Mirenia]

The issue was not only CMOS battery.
Had to do a reflow of CPU and GPU.

Now everything is working without problems