Fried Arduino mega 2560 / Ramps 1.4

Using Arduino IDE 1.x
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First of all, hi and thank you to help me,

Actually, I don't know if my question is ask in the right project, if not please refer me to the right place.

Context: I know how to use an Arduino with his ramps 1.4 for a 3D printer but when we talk about repairing and understand how it works, I am real newby.
So, I have been printing pieces for maybe two weeks and while the printer was printing, I touch the board to see if the fans were cooling the board correctly. (I have already printed maybe 3x 4 hours + print WITH the fans) The printer suddenly stop printing and the LCD screen became all white. As far as I know, any cable or wire have been disconnected during the manipulation. There was a fried electronic / plastic smell coming out of the power supply side of the board. At first sight, there is nothing different on the board appearance (Arduino mega and ramps 1.4).
I have also notice that the circled region on the picture was kind of hot during the print. I don't know if that is normal or if it means something.

I have no idea which component could have fired. Please give me a starting point about the problem and how could I repair it.

Thanks a lot

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I took pictures of the Ramps 1.4 and the Arduino mega 2560 (plugged). I also think that the burned smell came from the Ramps but I am not sure. Hope this information could help.

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UPDATE :

I have made some additional research and I could not fin what is my problem, but I have made some tests listed below (The Arduino was supply via the 5V USB cable port during the tests):

  • When the Arduino and the ramps are connected via USB, the LCD screen works but when it is connected to the power supply, the screen is all white.
  • When the two boards are connected to the power supply, the fried smell come back.
  • I am able to download the marlin firmware on the Arduino.
  • The 5V pin on the ramps and on the Arduino shows around 5.60V while the 3.3V pin on the Arduino shows 3.65V.
  • I measure the voltage on the 3.3V and the 5V regulators and both shows 5.6V which is strange for the 3.3V, because the 3.3V pin shows the good voltage.

If the problem is the 3.3V voltage regulator, is it possible/easy to change?