Arduino Mega 2560 r3

Dear Community :slight_smile:

due to needing more PWM-Pins (to control three different 12V LED-Strips via Transistors) for my project, I switched from Arduino Uno to a Mega 2560 r3 instead. Unfortunately it seems like it just stopped working (because as a newbie, I was trustful and naive enough to believe, that the arduino's automatic power supply-selection works as explained in the data sheet...)

That way I apparently fried it and now it gets no longer recognized as an USB-Device and the small sqare-kind of chip (ATMEL Mega16U2 1440) on the right side next to the USB-socket gets really hot instantaniously, when I power it over USB-cable.
If powered via Vin, this takes a little longer but in addition the power-regulator-transistor right above the Vin-Barrel-Connector gets hot as well.

These two parts are even pictured in this schematic:

[taken from: http://cdn.instructables.com/FSS/Q6FC/I0NOI8UM/FSSQ6FCI0NOI8UM.MEDIUM.jpg]
...and in this photo:

[taken from: http://www.electroschematics.com/wp-content/uploads/2013/01/Arduino-Mega-2560-Pinout.jpg]

I measured the Gate-Drain-Resistance and this is shortened for the external Vin-regulator, but in my opinion USB-powering should still work as normal. I've ordered a new Vin-regulator for replacement (there are some tutorials on that out there), but actually I don't think this will solve the problem for the USB-power-supply(?) (and therefore i did not find anything, neither how to replace it, nor where this one is placed on the PCB).

Thank you in advance for helping me :slight_smile:

Lenbus

Arduino's automatic power supply-selection works as is described. Arduino can be connected via USB and barrel jack at the same time and the power will be drained from the jack and it is switched to the USB right away after jack disconnecting. Switching is maintained with OA as comparator for VIN and 3.3V. Same for UNO and Mega (R3). Vin just bypasses input diode. I think, your problem was caused something else, like incorrect polarity or short circuit etc.
The 5V regulator can be hot if high current is drained, also if the input voltage is higher (let say 12V and 400mA). It is known deficiency. It is better to use lower voltage about 7-9V to avoid this. So, it is hard to say if the the voltage regulator is fried or not. Try to measure input current. However, if the small ATmega16U2 is getting hot, it is indicating that probably this chip has gone.
You have to use SMD rework soldering station to replace this chip with the hot air. For many Arduino owners it means that the board is wasted. On the other side, the price for the board is not so high in compare with the price for the parts, tools, effort and not guaranteed result. You must know if it worth.