Question Computer freezes Faulty Mainboard or CPU

[derpfromabove]

Around 2 weeks ago I learned the hard way why you shouldn't mix different manufacturer's SATA power cables after switching the old, stuffy case for a new one.
Fried 2 hard drives, a Blu Ray and a keyboard.

Once the fried hardware and wrong cable were replaced, a new problem popped up:
Sometimes, while doing something demanding (i.e. running a demanding game), the PC freezes up completely, forcing me to shut it down by holding down the power button, which isn't exactly healthy for the system

Did some troubleshooting of my own and here is what I did/find out:

• Replaced the wrong SATA power cable with the correct one
• Confirmed that all the other cables are the correct ones
• Replaced the fried hardware
  
  Now, on to the diagnostics I did:
  
  
• Freezes of this kind never occured prior to the case switch
• Full Virus scan confirmed that the PC is clean
• Freezes seem to only occur in demanding games, but do not seem to be prevented by lowering settings or closing all other problems
• Freezes have not occured outside of such demanding applications
• Time of freezes seems to be completely random. At times I can play for over an hour, at others it freezes on me within the first 10 minutes
• Temperature during freezes seems to be chilling at <60°C
• Nothing unusual seems to be popping up in the Windows Even Viewer's log of the time of the crash
  
  
• Checked SMART data of all drives- they are working perfectly fine at
• PSU seems to be providing the appropriate voltages

System components:
Mainboard- ASUS ROG STRIX B350-F Gaming
CPU- AMD Ryzen 7 1700
RAM- 2 x 8GB (forgot which it was)
GPU- ASUS 1070ti Cerberus
PSU- Corsair CX 550

Which brings me to the imortant question:
Which component is the cause of this, the Mainboard or the CPU? I currently lack the diagnostic tools needed to check if something got damaged and I can't exactly YOLO it and RMA both and hope the manufacturers figure it out. And I'd rather not pointlessly throw out money purchasing both a new Mobo and CPU if I only need one of those replaced.

 

[R_1]

my first suggestion after a power event is to test the RAM with memtest86 for 5 passes.
you can try booting to a new environment and see if the rest of the hardware is working. make a bootable linux USB drive and boot to linux. new OS, new drivers, if the freezing follows you here the problem is hardware.

Boot to a USB drive with linux on it. grab a USB drive, a copy of rufus and a linux distribution.
http://distrowatch.com/ has tons of differing linux distributions and download links. I personally am fond of linux mint with cinnamon.
https://rufus.ie/ the utility used to extract the ISO file to the USB drive.

use rufus to extract the selected ISO to the thumb drive. it will make the drive bootable and you can run linux from the drive once done.
Reboot into linux and proceed to test the hardware. connect to internet, watch videos, await problems.
if linux is good and stable the issue is most likely inside windows or otherwise software related.
this is a test of the hardware.