Why does VNC work when my laptop has no picture on the internal or external display?

Question

I have a late 2011 MacBook Pro (15-inch) running High Sierra (10.13.4).

My problem is that the display is blank and external displays connected via the Mini Displayport on the side don't recognize a signal (also display blank/searching for signal). Otherwise, the computer has no other issues: it starts up, runs programs, doesn't have difficulty with the processor or connecting to networks, etc.

How do I know this if the displays aren't working? Well, I was able to blindly start up a VNC server using the terminal and some luck, and can connect via VNC from another machine to see what I would expect to show up on the display (as well as to control it, etc.), which seems strange to me since if it was a graphics malfunction/issue I would expect VNC to also fail to show the display.

What could cause the internal and external display to not function but still allow VNC to display properly?

Answer 1

It's a hardware fault, for sure, likely caused by accumulated physical trauma. The display adapter has multiple logical components, and the last one which touches the signal is the circuit which enables the ports and sends the data over the wire. The part of the display adapter which helps the CPU determine how to generate the image which VNC accesses is upstream from the part which selects ports and puts the signal on their wires.