When applying 15VDC via the DC connector for external supply the onboard regulator starts of with 4.90V but gradually over a period of about quarter to half an hour climbs to 5.5V, measured at the exit of the voltage regulator on the board.
The voltage regulator is an AMS1117 5.0V SMD device.
The spec sheet shows it can be powerd with up to 18V.
I never applied more then 15V, and the load current of the Arduino has never been more then about 200mA.
This is without the USB connected.
Is it bust?