iPhone 6 keeps searching signal, faulty u_qpoet?

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iPhone 6

这款4.7英寸iPhone于2014年9月19日发布，是iPhone 6 Plus的缩小版。

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phonestore.uk @phonestoreuk

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iPhone 6 keeps searching signal, faulty u_qpoet?

Hi guys, I have an iPhone 6 here. The phone has signal issue, keeps searching. In the settings the ICCID, IMEI and Baseband are all present. Upon testing, I found no voltage detected on VPA_APT line. I know VPA_APT line is powered by U_QPOET chip, so I replaced the U_QPOET chip, unfortunately it made no difference, still no voltage on VPA_APT, phone still has no signal. I also tested the coils L4001_RF and L4002_RF, they both have 3.9V, which I think is normal. I don’t know where to go next. Any help would be appreciated!

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Do you also get IMEI displayed when typing *#06# in dialer? That grabs the IMEI straight from the baseband chip.

There's some pretty good info from this thread:

Constant searching, no signal..

由 Ben 完成的 2018年10月27日

Hi Ben, before replacing U_QPOET, yes IMEI came up when dialing *#06#. To be more specific, before replacing U_QPOET, the phone showed “no service”. But after replacing U_QPOET, the phone showed “searching”, no IMEI came up when dialing *#06#. I installed the U_QPOET twice, made no difference. :(

由 phonestore.uk 完成的 2018年10月27日

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Minho @refectio

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Interesting as I found a nearly identical question from last June on Jessa’s forum. The OP said that doing the U1/V1 jumpers solved the problem.

For the original No Service error, I would focus on the ASM/WTR and WFR. In one case, I found that the top layer of the ASM had shifted and reflowing it solved the issue. You should also fully probe the BBPMU.

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Do you also get IMEI displayed when typing *#06# in dialer? That grabs the IMEI straight from the baseband chip.

There's some pretty good info from this thread:

Constant searching, no signal.. — Ben
Hi Ben, before replacing U_QPOET, yes IMEI came up when dialing *#06#. To be more specific, before replacing U_QPOET, the phone showed “no service”. But after replacing U_QPOET, the phone showed “searching”, no IMEI came up when dialing *#06#. I installed the U_QPOET twice, made no difference. :( — phonestore.uk

A One Mobiles @aonemob 声誉积分: 1.2千 4 1 5 · Answer 1 · 2018-10-27T00:36:16-07:00

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A One Mobiles @aonemob

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Without the background to the device im kinda thinking that it may be liquid damage?

I would check that the line you mention against a known good board and make comparison.

Then i would check PM8019

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Hi, thanks for your reply. The phone is not liquid damaged. The board is clean. On a known good board 3.7 volatage is detected on VPA_APT line.

You mentioned the baseband PMU might have problem. I wonder, VPA_APT gets power from U_QPOET chip, how come will a faulty baseband PMU affect the VPA_APT?

由 phonestore.uk 完成的 2018年10月27日

No problem!

VPA_APT doesn't get power from PMU if you're not getting a reading from it you will need to follow that line and see what it connects to.

I would check zxw if you have, if not let me know I'll post a screen shot when I get back into work.

由 A One Mobiles 完成的 2018年10月27日

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