Proximity sensor issues

[iRevival]

Hey guys. I have two iPhones that have proximity sensors that don't shut the screen off. I'm not sure if the sensors themselves or if there's something wrong with how they're set up. One of them is an iPhone 4 and the other is on an iPhone 4S. They both have shiny black mid frames. Neither one of them have a screen that shuts off when on a phone call. This is obviously a pain in the ***.

I've tried many of the different fixes out there:

Ive replaced the proximity sensor flex cable on the 4
I've switched the screens on both
I put a piece of tape between the two sensors on both
I've covered the sensors with electrical tape with a pin hole through it on the 4
and now I'm lost.

You guys have any suggestions?

Still have to try a new sensor in the 4S.

[805 93003]

Try technique of darkening single piece of clear Scotch tape with black Sharpie pen. Place this single piece of blackened tape over both ports of the Sensors, then put the front assembly back on.

If before, you decide you want to know if the flex is even powered on, then make Call or use Voice Memos to test Sensor, use camera or another iPhone camera (not iPhone 5) to view the infrared light, to see if that is functioning.

[iRepair]

I've had a couple phones like this that I could not get the proximity sensor to work no matter what I did. I tried 3 or 4 different ribbons... i tried the coloring scotch tape, laying pieces of electrical tape, cutting pin sized holes... you name it... no matter what, I couldn't get it to work. Eventually I gave up and assumed it had to be a problem with the board... can anyone verify that it indeed can be a board problem?