Have you looked at the switch that tells the Mac when the lid is closed? That's often a reed switch and magnet. Reed switches have a tendency over time to get "sticky", and your 1400 may not know the lid is open, or it may be getting conflicting signals. You can sometimes unstick a switch by tapping in the vicinity or waving a magnet of opposite polarity near it. I don't know what kind of switch the 1400 uses, but a sticky switch certainly messed up my Wallstreet.

Click to expand...

Yeah, I thought about that, but the fact that it only happens when the lid is open, never when it is closed lead me to believe it is not the lid-open sensor. (I actually originally titled this thread "1400 keyboard lid sensor location?" before deciding that wasn't it.)

I have verified on a second 1400 that when the lid is closed, it ignores keyboard input. This leads me to believe that it is definitely the keyboard or controller. The fact that it happens with two keyboards, and with no keyboard at all, further leads me to believe that it is either the physical connector, or somewhere in the firmware relating to the keyboard.