Released on September 19, 2014, this 4.7" screen iPhone is the smaller version of the iPhone 6 Plus.

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Intermittent Cell Signal Issues Persisting After Troubleshooting

Hello All,

To introduce myself I am a professional repair technician who has gone through ISO 9001:2008 certification in mobile device repair with about 1 full year worth of repair experience and 100s of iPhone 6 devices fixed, and this still stumps me.

I know a lot of people have asked about this, but no one seems to be able to give a definitive answer, and I was hoping over the past few months maybe someone has stumbled upon a feasible solution.

We have three iPhone 6 phones in our shop, 2 we own, 1 customer's device all with the exact same symptomolgy: Intermittent service Searching/No Service. At random the device will connect to the towers with good service (3 to 4 bars) and again at random they will switch back to "searching/no service". This issue occurs on all the network types the phone is capable of operating on (AT&T's GSM and LTE and Verizon's CDMA and LTE)

We have confirmed that it is not the following:

-Date and Time are correct

-Toggled Airplane Mode

-Different SIM Card

-Toggle LTE on/off

-Different Network's SIM Card LTE on/off

-Reset Network Settings

-Factory Reset

-No liquid damage

-No apparent frame bending

-Multiple new primary cellular antennas (completely installed new charge ports, ensuring all grounding rings and sticker surfaces were cleaned before installation)

-Multiple new cellular interconnect coaxial cables (the one that runs the length of the motherboard on the device)

-Multiple new upper antenna interconnect flexes (the L shaped one at the top of the motherboard)

-No damage with a continuity reading to all coaxial connectors on the board to their respective pads

I've done what I feel like is a lot of research but keep turning up empty handed. It appears like this issue is caused by a chip on the motherboard that was not underfilled that has cracked or damaged solder joints, I just don't know which one. Logically it must be after the baseband but before the antenna amplifiers, so a switch of some kind? To my knowledge each frequency type/band has its own amplifier (GSM/CDMA/LTE etc.) but they all share the same modem (the baseband). Maybe I'm wrong though, just going on very unclear googling.

I am experienced with board level repair and troubleshooting, and I know it can be like opening a can of worms but I am confident and have nothing to lose in attempting a repair of this kind.

An indepth explanation of both the physical, electrical, and firmware structure of the iPhone's cellular antennas would go a *long* way for me if anyone can.

A little bit goes a long way, if anyone has any thoughts let me know!

Answer this question I have this problem too

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Hi William -

Did you ever figure out what was happening with those 6's ?

I have a similar problem, although trouble started out a different way. My iPhone 6 was drowned in the ocean. It was opened and battery removed and then dried out. From there it was cleaned up and everything worked except the back camera (would not auto-focus), the digitizer (rarely survives water damage) and the battery (also doesn't like getting wet).

After replacing those 3 parts everything seemed proper - the data was even intact. However the cellular connection is slightly weak and intermittently goes to No Service. The battery usage details show that the majority usage is spent on cellular. The WiFi and Bluetooth function perfectly.

Any suggestions on what to try next?

- Many thanks!

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Monte, it sounds like you are having a different issue entirely as a result of not only the ambient effects of liquid damage as well as the level of the cell signal. More likely you are dealing with corrosion that has eaten away at one of the grounding contacts for the primary cellular antennas, as you say your battery is getting eaten by your cell signal usually that means it is reaching "further" to connect to a tower. I would make sure that the *entire* phone has been thoroughly cleaned of all corrosion and any remaining minerals first. Then I would check all of the grounding contacts and connections for every antenna on the phone, notably the small one that bridges between the motherboard and the camera retaining bracket as it sounds like that is where a bulk of the corrosion had occurred.

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I have the complete same issue with my iPhone 6 ... 1 week later no random fix working again

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Deck the Halls
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If all bands and cellular services fail intermittently, maybe you should take a look at the baseband, baseband power supply and/or transceiver. If these chips have intermittent failures, the entire cellular function also fails intermittently.

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The way I was taught to check the baseband was by attempting to read the IMEI from the General>About menu in settings. Both the IMEI and the ICCID are present here. Is there a way to check the baseband power supply and transceiver?

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I reached out to Jessa at iPad Rehab and she believes that the BGA on the Baseband Chip is failing and that it would need to be reballed. She said that it was a staple failure on the iPhone 6 series. This process would be similar to that of the Touch IC except since that the Baseband is married to the motherboard it can not simply be replaced it must be reballed.

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Reballing the Baseband Chip is probably what needs to happen - unfortunately, that procedure is beyond my capabilities at the moment...

But thanks for the great advice and learning experience.

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Hi, the problem is caused by the baseband IC chip. You can double check this by dialling *# 06# If the screen is blank then its this chip. If the IMEI comes up (it will only show when you have a connection to the network), then its this Baseband chip. Checking under general settings will always show the IMEI even if the baseband chip is faulty.

The phone get bent a little in usage and back pockets, which breaks some of the solder connections under the chip. The only way to fix this is to remove the chip, clean all the old solder off, then reball/solder and refix the same chip which is married to the board. Trying to heat the chip and giving it a nudge will not work as you need to repair 2 specific solder points which will have already been cracked and damaged. This is a very skilled and specialised repair. Hope this helps. KH

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Agree with Khalid, it's the U1 and V1 Pads. I've had good success with this repair as Chris Long explains in his videos on Youtube. @refectio suggested this to me and have done 4 - 5 since with only one needing U_PMICRF Baseband power management IC replaced, but if baseband reball and jumpers do not fix, check U_ASM_RF antenna switch module ic chip, WTR1625L Transceiver chip IC U_WTR_RF, or Receiver IC U_WFR_RF WFR1620

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I have a theory as to what could be causing this issue as it is happening on my 6 plus too, all the hardware seems perfect and all software fixes have been tried.

I have noticed that the loud speaker module is acting more magnetised than normal at the bottom of the phone so much so that the magnet can pick up objects through the screen, something which I had previously not noticed.

With a strong enough magnetic force in the presence of the cellular antenna hardware connection at the top of the loudspeaker connection this could be causing signal interference on the cell antenna.

I do not have parts currently to test to see if this is in fact the cause unfortunately but this could be the cause.

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William Chabot will be eternally grateful.
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