Issue with voltage regulator

Hi everyone,

I started playing with my assembled printer this morning. I am planning on tuning it a bit because I won’t actually use it as a printer - for professional reasons, I only need the steppers - so I am testing it by sending Gcode using arduino and not Repetier.
I managed to drive the steppers a few times this morning and in the afternoon.
Now when I plug the USB cable, I have the red and green LEDs (6 and 5) lighting up, which is normal. When I plug in the alim, the LEDs turn out and a green one (JPV) blinks. Then it stops, and the red LED (5) start lighting up slowly. Then the green one lights up slowly too. I can’t use the board nor flash the firmware in that state (I get avrdude errors in arduino, as I did when trying to flash without shortening the JPROG pins).

Does someone have an idea of what it means, what has happened, and if my board is dead? If not, what can I do to make it work ?

Thanks a lot for your time.

EDIT : I found out that the voltage regulator gets really hot (can’t touch it), a few seconds after plugging the 15V alim in. It happens with and without the USB cable plugged in.

I checked the voltages at the GND, 5V, and 12V pins on the board (next to THERM1 and THERM 2), and also at the voltage regulator pins. GND and 12V are fine, but the 5V pin and the Out pin of the voltage regulator are at 1.4V. I guess it is not normal and it points out to an issue with the voltage regulator. If someone has insight on this, I’m all ears.