ideapad c340-15IWL random Blackscreen

[felix27]

Hello,
I am trying to fix a ideapad c340-15IWL with random blackscreen crashes, after witch the system is completly unresponsive, even on an external monitor. The blackscreens accur completly random no matter the load put on the system. You can sometimes run cinebench succesfully only to have the system blackscreen five minutes later while doing nothing. I have already tried to resolder several chips and have resoldered all contacts of the dimm slot. I have also tried different ram, wifi-card and SSDs, with the same effect. I had another lenovo with a similar issue, which was resolved after removing the dimm. The problem is that this system has no onboard RAM. Does anbody know what could be wrong? I was maybe thinking cpu solder contacts but I am not sure voltages seem correct, even when crashing.
Thanks for your help.

[mcplslg123]

Does one phase of the cpu vcore voltage disappears when BSOD happens?

[felix27]

Yes, vcore drops to 0.

[mcplslg123]

De solder all the mosfets on vcore. Put some flux and fresh solder on PCB as well as pin/pads of mosfets and then proceed to resolder them. It may help you.

However, if the issue persists replace all vcore mosfets along with PWM/Driver IC.

Going by my experience with lenovo's, merely soldering them with fresh solder and paste solves it.

The issue is 'coz of very bad quality of PCB and it doesnt tolerate heat at all. So be careful not to apply too much heat ,else nearby components may just fly away.