Screen turns on by itself - dock connector?

I got a broken iPhone from eBay, when I put it back together it worked ok, but a ribbon cable on the dock connector assembly was broken. The microphone etc. did not work.

I bought a "new" dock assembly on eBay, but since putting everything back together again the screen lights up and displays the unlock slider about every 20 seconds. It does not do this when playing music, or when plugged into the computer.

Having googled it looks like it might be a faulty dock connector - does anyone know whether or not this is the case? I also replaced the headphone assembly and vibration motor, but I installed these yesterday before the dock connector.