Envy 15 (7th Gen Intel i7) random shutdowns. Please help.

[turborex]

Hello folks.

I bought this machine brand new. It ran fine for nearly 6 years. Lately, it has been plagued with random shut downs without warning and I have nearly pulled my remaining hair out trying to troubleshoot the issue.

I have no electronics knowledge though if anyone can guide in the right direction this would be awesome.

Description:

----System will randomly turn off i.e complete power loss. There is no specific timing. Sometimes it may run normally for a couple of days without the issue but once it starts; it becomes more frequent, and then, it sort of 'levels off' for some time until it starts again.

----Lately, these hiccups have been more frequent and the laptop wont be able to complete a boot until after I have let it sit and rest for a while.

----There is no trigger for it which I could identify though it seems correlated with fluctuations in CPU / power load. The laptop has an aluminum body however I am not sure if any there is any earthing issue or short.

----Shutdowns can happen anytime, in Windows, during boot, at Windows setup and even in the BIOS/UEFI screens.

---- CPU temps are perfectly fine and don't appear to be the root cause.

---- This occurs both on mains power and on battery. Not a generalization, but it seems a bit more frequent on mains.

----Laptop sometimes refuses to awake from 'sleep' mode, comes on with only fan spinning and then needs a hard reset. It may be that the sudden 'shutdown' occurred in sleep.

Efforts so far (in order):

(1) Swapped the SSD to HDD, tried a new HDD and back. (No change).

(2) Changed the RAM. (Made a slight difference, it seems more frequent on the older 8gbstick than the new 16gb stick)

(3) Replaced battery. The previous one was quite swollen which has been the only major physical issue with the laptop. (No difference at all, also ran exclusively on either battery or mains but still no difference.)

(4) Replaced the thermal paste and cleaned the fan. (This bought temps down by a couple of degrees, though like I mentioned before, temps haven't been an issue. No noticeable difference)

(5) Close inspection of the board  (under a phone magnifier) appeared to show some minor humidity / liquid damage (limescale kinda stuff) on and around some mosfets and their surrounding areas. I cleaned it with some iso and WD40. This didnt help much.

(6) Updated the BIOS  to F.62 (made no difference at all)

Any help would be sincerely appreciated. Is there a checklist for disconnecting parts such as USB, LAN etc so as to check any broken down offending part?