9V Vin powered Mega - 3V instead of 5V I'm experiencing an issue with an Arduino Mega 2560 :
I powered the board through the Vin using a +24 --> 9V voltage regulator. When I power the board and measure the 5V output from the board, the voltage quickly drops from 5 to ~3V within seconds.

However, while powering with USB, the 5V output from the board gives us a clear 4.8V.

I have checked the 9V Voltage regulator (connected to the Vin), and it has a +24V input which remains stable (as should the 9V).

Any thoughts ?
So, according to the comments the main problem should be a thermal protection in LM7809C regulator.

The voltage drop between regulator's input and output is about 15 Volts and even with current consumption about 150mA it means 2.25W of power dissipation on it.

For such a big difference between input and output voltage switching regulator is recommended. (Or 9V power supply instead of 24V)

And it is not possible to have 2mA current consumption. I've just measured power consumption of bare Arduino Mega 2560 and it is 81mA through barrel jack input (9V) without anything on it. Not even blinking Led. So if you've measured for example 0.2A it's not 2mA but 200mA