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Still searching after baseband reball - not the usual issue

Got an iPhone 6 for repair, was showing no modem firmware and no Imei after the 06 dial test. Done monkey see monkey do, jumped 2 pins, reballed baseband and got half of the problem solved. Now it shows modem firmware and IMEI number is listed in iPhone Info, however the *#06 # test dial keeps not showing IMEI and phone still stuck on searching. SIM is correctly detected when inserted and NO SIM warning prompts as it should. It seems baseband is working fine or am I missing something ?

Anyone had a similar issue solved and can provide some insight ? Thanks

Tried replacing U_ASM_RF as well, no joy. I'm a bit at a loss here, the other two candidates (WTR1625L and U_WFR_RF) look pretty hard to replace and I don't even seem to have the right stencils. Any reasonable way to test baseband further or should I add this to the pile of spare boards ?

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It really boils down to how much time you want to waste vs. how much you hope to get out of an iPhone 6.

No IMEI would not be WTR in my opinion (I think that you may have an issue with your BB_CPU but I am not so good with baseband troubleshooting), but if you want to replace it, it will be easy to reball compared to the BB_CPU.

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@rany It's a 64Gb, so there's still some value and I can dedicate another couple of hours work to it, especially thinking the BB already seems to be fixed. I didn't even think about troubleshooting the BB_CPU, heaven knows why, thanks for the hint. I've also noticed ZXW has got resistance values for this phone BB..I don't especially love the idea of another reball, but it would be an interesting alternative. Will update with the outcomes.

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Did you do short or long jumpers as part of your repair?

Short jumpers don't always work and have a higher return rate. The Intro group on FB has all kinds of testimonials about this. Long jumpers seem to solve the problem but removing the SIM reader can be a pain. I would check for proper continuity on the V1 pad to the TP under the SIM reader. There may be a break on the trace internally within the pcb.

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I did short jumpers. However, I forgot to mention in my question, jumpers were properly sealed with UV curable rosin and tested for continuity before reinstalling Baseband IC and got resistance in the range of 350/Y1 pad and 435/V1 pad, which seem to be correct figures, is that right ?

I agree short jumpers are quite a risk.. if not sealed they are very short and might be unreliable as much as the weak original rails.

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I don't believe the UV curable mask offers any structural strength, it just helps to hold down the jumpers during the soldering and covers any exposed wire.

The question is, is the V1 pad connecting everywhere it should? Just because you measure 435 from your testing point, doesn't mean that signal is getting all the way to the CPU (or vice-versa). Food for thought...

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@refectio I would expect it to work if condition is similar to that of a working one, at least in theory. I wonder how a longer jumper would possibly make a difference if rail integrity is there..or is there anything I'm not taking into account ?

I'm prepared to replace the Sim tray, but I'd need some encouragement =;)

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That trace goes from BB_CPU to the CPU. It doesn't necessarily do it in a strait line nor via just one layer. So if that trace is damaged in any way, it ill fail.

It may look something like this:

BB_CPU--------|xxxxxxxx|xxxxxxxxxxxx|--------------------CPU

xxxxxxxxxxxxx|-----------|xxxxxxxxxxxx|

xxxxxxxxxxxxxxxxxxxxx|------------------|

(ignore the "x's", they're just for proper formatting)

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