iphone 4 proximity sensor woes

[Tucson Techie]

Hello to all the iphone gurus out there, I need some advice.

For some reason I don't quite understand whenever I replace the power/proximity sensor cable on an iPhone 4 GSM or CDMA, the proximity sensor doesn't work. I now remove the LCD assembly when doing this repair because that way I can see the positioning of the proximity and ambient light sensors in the mid-frame and I can also verify that the light-filtering foam pad is in place. The last several of these repairs I've done, the sensors look aligned correctly and the pad is in place, yet the darned proximity sensor almost never works.

This rarely happens when I replace the LCD assemblies, but it happens 80% of the time when I replace the power cable. I have purchased power cables from different suppliers and it doesn't seem to make a difference. Very, very, frustrating.

The majority of these phones have their original LCD assemblies. The foam pad looks good.

I've tried the black marker "fix" and it doesn't work for me.

Those of you who have a lot of experience replacing these proximity sensor / power cables, how do you get around this problem? Do you use the electrical tape fix even when the foam pad is still there? The foam pad fix seems to apply to new after-market screen replacements where the lighter colored inner glass allows too much ambient light to filter in. In my case, the screens are the original OEM's. Also, in my case, the original foam pad is still there. I can't imagine I've managed to buy 6 defective cables in a row from different suppliers.

Any ideas. suggestions?

Thanks!