The Bios battery was replaced a couple of years ago, but I suspect it’s the power supply as there is no life at all.

If the battery was gone it should still power the screen minimally. I'll probably swap it anyway, just to test.

Sources: 800D, Sooloos Control:15, Sony BDP-S790,Humax Freesat+
Control: 861v4, HD621
Front: DSP3100
Centre: DSP3100HC
Rear: DSP3100
Screen: Samsung UE50H6400
Projector: MF-10