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Released on September 19, 2014, this 4.7" screen iPhone is the smaller version of the iPhone 6 Plus. Identifiable by the model numbers A1549, A1586, and A1589.

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Phone dead after Tristar replacement

Hi all, I'm hoping for some assistance from somebody out there. Working on an iPhone 6; phone was working perfectly in all respects except for one thing - while it would charge a partially charged battery it wouldn't charge a flat battery at all. After trying different batteries and using my own charge port and doing some measurements with the multi-meter I finally decided to replace Tristar. I did this carefully and once finished I put the board back in the housing temporarily to test it. I first used a partially charged battery; the phone booted no problem and began to charge the battery. I then tried a known good battery which I'd allowed to go flat; the board began charging the battery and booted a few minutes later, bingo! I let it charge for a while until there was about 15% in the battery then disconnected it and switched it off in order to properly reassemble it in the housing. Did that, connected the screen and turned it on....nothing! Phone is now completely dead; it shows 0A on my USB ammeter but on the DCPS it is pulling a small and constantly fluctuating current of approx. 30mA but it's up and down all over the place (but always less than 100mA). When I try to measure voltages they are also fluctuating wildly and I can't get decent readings anywhere on the main lines. There are no shorts (I've physically checked every large and medium-sized cap on the board in continuity mode) and strangely in diode mode everything seems to be reading correctly when compared to my known-good IP6 board (which definitely still works fine). When reassembling it I didn't use heat to replace the Tristar/Tigris large shield I just used my iron with a tiny bit of solder & flux. I've since replaced Tigris but no change. I'm starting to think it may be PMIC but still have a niggling feeling that it's something dead simple which I'm missing. I've been over board under the microscope at x20 but can't see anything unusual. Help!!

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So if I understand correctly, the phone worked after the Tristar replacement but before putting the shield back on. Then when you soldered the shield back in place and re-assembled, it wouldn't boot - correct? When you removed the shield to probe (did you?), did the board boot and charge properly or was it permanently dead?

I once had a phone that did something just wouldn't work with the back shield in place.

If the shield is currently off, try connecting it with a known-good dock and battery just to see if it boots and is recognized by iTunes. If it isn't, then you have troubleshoot it just like any other dead board. I would consider removing Tristar and trying again as that is the main variable here. But otherwise, you will just have to check all of the voltages.

If the shield is still on, try checking the main voltages that you have access to to see if anything is off. If not, then remove the shield and proceed as mentioned above.

Report back and we'll see where to look at next.

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Hi, thanks for your response. I went back and replaced Tristar again and tried the board on the DCPS and it boots fine. When I try a known-good battery it also boots fine, but still won't charge from USB. I'm reluctant to continually pull and replace Tristars on this board as I think there's something else going on. I'm getting 5.2v on PP5VO_USB but battery voltage on VCC_MAIN so not too sure what's happening. I may replace Q1403 just to rule it out?


PP5V0_USB is just the voltage from the USB port. You could always measure that independently just to be sure.


I'm having the exact same problem on a 6+.


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