Extreme motherboard temperatures while drawing power

Hello everyone, 

I have an odd problem that I can not seem to narrow down. 

The motherboard in my 2013 Alienware 17R1 is super heating on the upper left hand corner where the DC jack plugs into the motherboard and down to about the HDMI port below that.  An IR temperature probe shows areas hitting 120c.  The temps rise very quickly when the system is drawing power ( in instances like gaming ) and return to mildly warm when the system is idle or I am just browsing the internet. 

I have already ruled out all of the internal components with the exception of the motherboard which I know of know way short of buying a new one to test.  

I have removed the WiFi, mSATA, HDD, GPU and the problem still happens.  The odd thing is if I unplug the adaptor the problem disappears completely , presumably because the system is drawing power from the battery of course and not the AC adaptor.  

I have tested the AC adaptor and the AC plug and both show 19 volts when using my multi meter, but I don't know if that will rule out the AC port as a culprit.  I have ordered a new one in the meantime but it will take a bit to get here.  

I was hoping someone might have some idea what could be causing this.  

I should add that the GPU was changed out from a 780m to a 980m because the 780m died, but even after removing the GPU and running on iGPU the heat is still there albeit not as bad, presumably because the system is drawing a lot less power.  

All system defaults have been reset and I re-flashed the system bios just in case.  I even replaced the coin cell battery because I was out of ideas.  

Any help would be great!

Thank you!