I picked up a second hand N900 recently and one thing has been troubling me with it.

Most of the time the touch screen does not respond unless the keyboard is open. Very occasionally it'll work properly closed from a reboot.

It works 100% of the time with the keyboard open. I've reflashed it so I don't think it's software. Is there a connector or switch/sensor that determines if the keyboard is slid out or not that could be affecting the touch screen?