Oh wow! Useful thread, thanks guys.
I too have a Lumia 930 which I love to bits. I have had it a year now, however recently it has been turning the screen off as soon as I dial a number and I have to press the on button several times to get the screen to wake up so I can switch it to speaker
or enter selection numbers etc. REALLY irritating!
It so happens that for Christmas my wife gave me a little cleaning gadget with a brush on one end and a silicon rubber "poker" on the other. This was perfect for cleaning the sensor area of the phone and the hole where the ear-piece is. I then rubbed thoroughly
with a microfiber cloth. This will have squeezed the screen somewhat which may have been the fix, but in any case for the moment my 930 is now working perfectly again.
So once again, thanks for all the input which has identified the problem for me too.
David