I recently acquired a Lumia 920 and changed providers from Sprint to AT&T so that I could get the 920. So far I like the phone but ran into an interesting problem. Today I needed to dial into a conference bridge, so I browsed for my saved contact that I use for this and hit call. Usually the first thing I do after the phone “app” comes up is hit mute, but before I could do that, the screen went dark.

I assumed that this had something to do with how the phone will turn off the screen when you have the phone up to your ear, and it’s a feature I quit enjoy. Today that feature seemed to be working too well. The phone was still 100% operational, I just couldn’t interact with it. Unfortunately, this conference bridge will repeatedly continue to ask you for your access code and not drop the call. After enough prompts, it will redirect you to an operator, which took even more time (ironically it’s an AT&T conference bridge). I ended up just putting the phone down and going online to search for a way to reset the phone.

To perform a soft reset, press and hold the power button and volume down button for about 10 seconds. You should feel the phone vibrate.

I wanted to see if the problem re-occurred, but did not want to keep soft resetting my phone. I decided to try calling my voice mail. Again, the screen went dark, but this time, after a few voice prompts for my pin, I was disconnected from my voice mail and my screen came back. So at least now I had a easy way to reproduce the problem.

After some more searching I found several threads on various forums of people complaining of the same problem. Most of the solutions involved blowing in, on and around various parts of the phone. Finally I read a post by someone who said his screen protector was the cause of the problem. Yes, I did have a screen protector on my phone, and I probably haven't used the phone function since I put it on.

Peeling back the upper right corner of the screen protector, I exposed the proximity sensor and tried my test call to voice mail. The screen stayed illuminated. As soon as I put the screen protector back down, the screen turned off. The proximity sensor is located just above the N in the word Nokia at the top right of the phone. I could barely make out the sensor thru the screen protector.

Simple Solution: Cut off a small piece of the screen protector so that it no longer covers the proximity sensor.