Thanks for the information!
Here's one not listed. I was at a class one day and my machine simply died! I had barely used it, had bought it on eBay and was VERY disappointed.
I figured out it was not dead. When I was threading it I had accidentally turned the dimmer for the display all the way down! Since I couldn't see the display I couldn't press the "sew" icon, or the up needle icon, you get the drift. Turning the machine off and on, trying a different cord, none of it would work without pushing the sew button.
It was a tiny wheel that turns left and right to adjust the brightness. On my machine is it behind the front wall, on top, next to the sideways thread spindle.