No screen backlight, no sound on SAIO v0.5E1

[Glyph]

Hi
I tried to turn on my GBZ after a long period on a shelf, but the battery was flat, so I plugged it in to charge.
Then, still in charge, it booted and worked a couple of times but at some point, the screen went black suddenly. I still see the LCD kinda working when tilting the screen, but it's like the backlight is broken. I tried to plug it to my TV via HDMI, but it does not seem to output any signal too.
Last thing, I have sound coming out through the mini jack but not on the speaker...

Is there any fuse or anything I could check to see if it's coming from the Pi or the board itself ?

Thanks you very much for your help.
Al