It sounds like a fuse. It’s strange that the fuse can’t be accessed from the back of the amp, but it’s French, and foreign stuff can be a little idiosyncratic. Unplug it, open it up and have a look. That's a nice amplifier.
Why did my amp just crash and burn ?
I just installed a new set of AQ Robin Hood Zero cables. A little hiss sound from the speakers prompted me to adjust the spade connecters just a little on the amp. Then low and behold , the amp just cuts off and currently appears dead as a doornail.
What just happened and needless to say this is an absolute bummer.