Hey guys I have an iPhone 3G that when it's not plugged in it will turn off after about 15-30 seconds of not being used and being in sleep mode. When it's plugged in it doesn't have this problem at all. Also, you can use it for as long as the battery will last without it having this problem.

A little backstory on this device.

I got it off of eBay and the guy said it had some water damage (something to the effect that he had it with him hunting (bad idea) and it fell into a puddle). He replaced the LCD and it was working again. When I got it I had to replace the touch screen as well because that wasn't working. The battery also wouldn't hold a charge so I replaced that. Everything works on it now except the above problem. Oh also if I launch the camera it makes it restart (probably water damage issue).

Any thoughts on why it might be having this problem? Could it be the dock connector assembly maybe?