Just had my HTC Desire HD (or shortened as DHD) for a few months now, been happy using it but then I start to notice a problem with its proximity sensor.
Symptom: when making a short phone call the screen is dimmed and stays so for several minutes, this causes more battery usage. The bigger problem is when I make a long phone call, the screen went turned off after some period and didn’t come back on when I move away the phone from my face (while it should).
After asking on XDA Developer it turn out that my DHD is having problem with wrong setting on its proximity sensor. What should happen when making call is that the screen will turn off (not dimmed) and will turn back on when the phone is moved away from user’s face.
Solution is to recalibrate the proximity sensor’s settings, this by default there is no way to setting it as it should have been setup automatically. Fortunately leppie wrote a program to recalibrate proximity sensor which can be downloaded here: [APP] DHD Proximity Sensor Recalibrator 1.4 (14-Mar-11)
I set my DHD with Low Threshold to 10 and High Threshold to 11, after that proximity sensor seems to work properly, screen went off once I put DHD close to my face and went back on if I move it away from my face.