Arduino heat problem

Hello, good morning.

Currently i'm having one problem with my Arduino, related to the voltage regulator.

When I plug my arduino directly to the USB, my Voltage Regulator gets really hot and after few seconds all the led lights lose bright and I lose USB connectivity to the arduino.

What is strange is that there are 3 different situations:

1 - When I plug just the arduino in the USB cable = VR really HOT

2 - When I first plug external power supply AND THEN plug USB cable JUST in the Arduino = VR ok, not getting hot.

3 - In situation #2, when I do it WITH the Ethernet Shield, it starts getting hot.

Do you have any knowledge to share about this?


Something wrong with power source circuit. Which Arduino exactly?. Genuine Arduino Mega or UNO has P-MOSFET which acts as switch between jack and USB and his actuator is OA as comparator - compares 3.3V against Vin from jack plug. Check the transistor and OA first, 5V regulator seems to be ok according the situation #2.