Hi, thanks by advance for reading

My fireface 400 has suddenly developped a  problem :
When I power it on , all the front leds light up, the host led also, turning red to green...all seems to be ok.
and after a few minutes,  all the lights turn off.

The problem arrived after two days of intense work ( during these two days, the FF remained plugged and on...but it wasn't the first time for the FF400, to be at work several hours without any pause.)

During the 3 ou 4 minutes, when all seem normal, the FF is recognized by my laptop, I can open and run my projects in cubase (artist) with no problem.
And suddenly, the fireface disappears, looking like not alimented ( and it's the case in my opinion...)

When I unplug the DC, connecting the fireface only by the firewire bus, all it's ok.
When I connect the fireface by the firewire bus, but with the power supply plugged (but, with the button switching between ext and bus, turned on the bus), the FF400 turns off after 3 ou 4 mn.

I don't have a DC 12v to verify if the problem is inside the FF or just in the external PSU ... I'll try to find one.

With those elements, do you think that's a problem inside the fireface ( DC converter burnt ) or just the PSU ?

Big thanks. (and sorry for my english coming from Mars )