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

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Does this cap confirm baseband is present and cause no-boot if missing

Hi all, working on an iPhone 6 which wouldn't charge or connect to iTunes but boots fine from a known-good battery (or did). Having done some metering I decided to replace Tristar and that appeared to go well with 36 nice shiny pads tinned and wicked, and the new A3 chip (Chinese) seemed to go on fine. However when I tried it again it won't boot from the battery it just boot-loops on the Apple logo, so I had a much closer look around the board in the general area and found that I'd accidentally pulled off a cap when removing the (copious) Kaptan tape I'd used. The chip is C3801_RF on the V_REG 2V line. The interesting thing is that the schematic shows an entry beside this cap which says 'MAKE BASE=TRUE' and I'm wondering if this cap provides confirmation that the baseband chip is installed, without which the phone continually boot-loops trying to find the baseband? Anybody come across this before and am I completely on the wrong track? Any other suggestions? I'm going to replace the cap when I get home!

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I would certainly replace the cap, especially one of that size. As for the cap providing information...no. All a cap does is store energy. That said, the cap provides this energy to the IC's when instant energy demands show up and the inherit inductance of the PCB impeded quick delivery of said energy from PMU_RF.

During bootup, this ability to deliver some juice quickly may make the difference between BB booting properly or not. Replace it and get back to us, I'd love to hear the outcome. I would also check for any other components that may have been accidentally removed.

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Hi, replaced the cap but no change. Before I changed the Tristar the phone booted from battery although it couldn't charge or be seen by iTunes. Maybe I've messed up the Tristar replacement or the chip was bad (it was a cheap one from China) so maybe I should re-do that? However I always understood that Tristar wasn't a boot/power problem but a charging/USB problem, so could the phone boot from battery even with a faulty Tristar or does Tristar have to be present/good for the phone to boot at all? Grateful for any clues to this one...

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I think you have it right...either bad placement or bad chip. It is required for proper boot and if that is the only thing you changed...I would suggest removing it, cleaning pads again, either reballing the original or the replacement and trying again. You sound experienced enough to know to ensure pin 1 location to pad A1 so it may have shifted a bit and bridged... are there any shorted caps around it? are correct voltages present on the caps?

@refectio is a Whiz on repairs and is a wealth of knowledge...you'll get it going :)

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Hi, thanks for this. I think this may be the case; I had another close look at the Tristar under the microscope and I'm starting to think it's a little off-centre. It's definitely oriented the right way with pin1 to A1 but although it looked fine while I was doing and I couldn't see any pads on any side when looking down on it I'm now thinking it has shifted slightly and may have bridged. I have 5 new 1610A3's arriving today so I'm going to do as you suggest and take the old one off, do a really thorough job of cleaning and preparing the pads and then carefully re-fit a new Tristar. Hopefully that'll sort it out! Thanks

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Let us know how it goes.

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George Wright will be eternally grateful.
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