There is also probably the grounding for the external case. This is a troublesome ribbon cable. I'm beginning to think that these students should have had more supervision in this teardown since they seem unaware of the risks involved in mains connected devices, when capacitors may be involved. It is possible that their model doesn't have case grounding but there is clearly a need for adult supervision.

I advise against using a screwdriver to remove the darkness control knob. That risks scratches and cracking the knob or post. If you know that the item can be pulled out safely, I suggest using a loop of paracord. That spreads the stress along the entire knob.