Why could my Black Screen of Death be so particularly stubborn?

I'm having the dreaded Black Screen of Death with my Steam Deck where it seems to operate completely fine, including the touchscreen, but the display simply will not turn on.

• It works when plugged in to an external monitor
• BIOS doesn't show up on the internal display (again, only with an external monitor)
• Internal screen doesn't show up as an option in Display Settings in Desktop Mode, nor using xrandr, nor while SSH'd into it from another computer.
• Have tried wiping, reimaging, factory resetting, the Volume + and ... button trick to try and reset it... nothing works.

I've tried the iFixit screen replacement, and... nada. Replaced both the screen and the cable, and I'm about 99.99% sure I did it right (following all the instructions to the letter). And still nothing.

Valve will not RMA it because I live in a country where it's not officially sold, so figuring I had nothing else to lose, I stripped it down again and reseated all the cables. And this time... the fan doesn't spin up either.

Does this mean I've got a faulty motherboard?