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Repair information and guides for the fifth generation of iPhone. Model: A1387

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Proximity sensor not working after screen change.

I replaced the screen on my white iPhone 4S 16GB. Now the ambient light sensor works but the proximity sensor does not.

However when I take the proximity sensor out of the case housing (removing the retention clip and laying it downwards) it detects my hand or anything close by and works.

The replacement screen has a filter over the sensor bar, and it has a small divider bar in it. I've tried the sharpie trick, placing tape and it doesn't seem to work :(

There's also a foam pad that is already there but it didn't seem to make it work in the first place.

What is going wrong?

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In the photo below, the red area is where I placed the tape over. The orange arrow is pointing to where there's a piece of glass in the frame that seems to sit in front of the sensor circled red in the picture above.

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I've tested the sensors again. When it's not installed in the phone frame it will work. When it is in the frame (with the black retention clip on), it doesn't work. I can see the sensors through the frame holes and even placing my finger right on it won't make the screen turn off. I found that using a metallic tweezer in front of the sensors when in the frame, causes it to work, although only when really close.

Now with the phone screen installed properly the metal tweezers works but not very well.

I'm going to try for a new proximity sensor I think.

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I've replaced the proximity sensor and it doesn't seem to fix it. It's the exact same issue, if I hold a metal tweezer near the sensor it will activate. I'm guessing this has nothing to do with the sensor or the screen as it doesn't work even when the screen is off.

I've noticed on the front to the left there's a small glass piece at a 45 degree angle, which seems to be where this thing behind the earpiece speaker goes (see red circle on attached image). What is that thing?

I'm trying to figure out why it won't work on one phone, but will on another.

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This could be a few different things. One thing is that the glass replacement you purchase doesn't have the same proximity sensor type paint and your proximity sensor flex is not able to go through the glass. The white screens are very finicky especially when it comes to the proximity sensor issue. Try to make sure the gasket is line up properly with the housing, lined up on the glass and not damaged so there is not light leak. Light leak is usually why the proximity sensor stops working. If all that fails, retest your old screen to see if it works on the old screen, if so, you know it's your screen. You can then return that screen if that is the case for a replacement one that will work. Make sure the proximity sensor is also all lined up as it is very easy to be off during installation and will not work. Other thing it could be is a failing flex cable but since it works, sounds to be more like the screen itself.

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Thanks for your reply. The gasket around the sensor is still there, the sensor is in the phone frame lined up and it all looks like it should work fine. It is baffling me. I can see a flashing light when I use a low quality camera phone to view the sensor area.

I can't use my old screen as it has been damaged and cant see anything at all. Although when I look at the filtered area it is exactly the same and lined up in the same way. I'm guessing a replacement proximity sensor is my next step?

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You said you tried the sharpie and tape trick? If I am thinking about that correctly, it's were you take scotch tape and put it over the glass where the sensor sits and you use a sharpie to color that in right?

At the end of the day, if that trick doesnt work it has to be the glass. The glass is just not letting in the correct amount of light or it's letting in too much and never gets triggered. I have used the tape trick a lot in the early years or 4 and 4s repairs, but didnt have to once the quality of the glass and manufacturing process was better.

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Yes I put tape over the area in the red rectangle on the 2nd photo in my question. When you mean glass, do you mean the little piece of glass that sits on the left side of it (indicated by the orange arrow in my 2nd photo)?

I put the coloured tape on the frame, then put the phone glass/lcd on top of it (to assemble the phone).

I've even tried the sensor without the screen on, and it doesn't work when it's placed in the phone chassis, only when it's placed outside of it. I've got a friends black 4S that I'm fixing and I'll be testing to see if the sensor works when that screen is off too.

I can only think that the chassis is the problem after this, I can't see why the sensor wouldn't work, even when I've got the screen off.

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I actually put the tape on the display itself. Flip the lcd assembly over and youll see where the proximity sensor goes. Put a small piece of tape on there (the actual glass) not the frame and lightly darken it. In theory, this should have the same result as what you are doing, but I've never taped the frame. I only tape the back of the glass on the lcd. I hope that's not too confusing.

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I see what you mean, I was thinking you meant to put the tape on top of the screen which would be visible and a bit unsightly. I'll try it but I'm not too hopeful of it working.

Last resort will be to try a different phone frame and see if it functions then.

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I figured it out. Unfortunately it might not be of any use to anyone which is a shame.

Turns out it is the logic board. I have a friends iPhone 4S that works fine in the proximity sensor area and I tested the following:

  • The new glass/lcd on the working 4S. Sensor works fine.
  • Proximity sensor replacement with the new glass/lcd on the working 4S. Sensor works fine.
  • Proximity sensor replacement with the working 4S's original screen/glass. Sensor works fine.
  • Logic board swap into the working 4S's chassis/proximity sensor/original screen & glass. Sensor no longer works.

So I don't know what's wrong with the white 4S's board but it seems it doesn't seem to work with functioning parts. Everything else works fine, just the proximity sensor is messed up. I'll have to use it as an iPod or something now.

Thanks to all that have offered help.

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I have a hard time believing it is the motherboard as this is the hardest thing to get to work on this model iPhone. If the proximity sensor works when not installed as stated before, it is not the motherboard. It has something to do with the alignment of all components or a faulty piece of glass. It is very tricky to get right. I have spent many of hours on these at times. Hundreds and hundreds of them. Keep working at it with original parts if possible and you will get it working.

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Well that baffles me too, but when I swap the logic board from another 4S, into the phone with the same chassis, proximity sensor and glass that supposedly doesn't work, it works perfectly. When I put the original logic board into another phone with a black screen, that also worked, the sensor fails to respond.

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