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Samsung Focus cell phone turning off mysteriously when making phone calls

February 23, 2012

A few days ago my girlfriend came from work all revved up because her phone was turning off when placing calls. She also claimed that she had to power cycle it to have it working again… and of course she asked me to have a look.

The first thing I tried of course was to try to repro the problem by calling myself from her phone and just as she said the phone turned off immediately after placing the call. That was odd. But then a few seconds later my phone started to ring… the phone wasn’t dead after all.


Not really. It turns out that Windows Phone 7 has this nifty feature where the phone screen is turned off when the phone is next to your ear.

The way they do this is by using an InfraRed proximity sensor (circled in red below) which works by sending an IR beam and measuring how much is reflected. The closer a solid object is to the sensor the more is reflected and viceversa.


You can see that the the protection screen in the phone has a couple of cuts precisely to avoid interfering with the sensor.

The problem

The problem was that the sensor openings got dirty so most of the beam was reflected back by the dirt giving a false indication that there was something close to the phone therefore turning the screen off.

The fix

Wipe!. Voila.


From → Windows Phone 7

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