iPhone 5S - Issues after Tristar replacement

[iguystechshop]

It's not entirely clear to me if the iPhone section is purely for data recovery situations, or if general iPhone board repair issues can be posted as well. Obviously please let me know if the former is the case and my question is inappropriate for the forum.

Anyway, have a 5S here that had classic Tristar failure symptoms. Replaced Tristar, went smoothly, but afterwards the phone would not boot. Replaced Tristar again with an IC from a different vendor, same result. VCC_MAIN is there, 1v8 is there. No response from iTunes. Checked for any obvious issues around Tristar and did find that I caused Q2 to lift. I know the phone will boot without Q2, but went ahead and reballed and replaced it since it needed to be done anyway. No change. Inspected other nearby components for any more issues and did not find anything obvious to my eyes.

I'm very new to the troubleshooting aspect of board repair, especially for iPhones. So I'm just looking for some direction at this point as plenty of my own research to try to find someone that had a similar issue has turned up very little and certainly nothing helpful.

 

[jessa]

Did you overheat bb_cpu on opposite side of the board? Pull shield and check for signs of heat. Also check to see if you have lost little peckers near dock from not pulling the sticker before putting heat on the board. And use known good dock not original dock from the phone. Boot off D.C. Power supply to see what current draw is.

 

[iguystechshop]

No Title

Overheating is certainly possible. Still getting dialed into heat and air settings on my Hakko 810. With that said, no signs of heat on bb_cpu though (which I assume is U1_RF) as far as I can tell. I remove all stickers before applying heat and little peckers in that area look good and feel solid. No sign of solder balls or loose components around U1_RF either. See attached photos.

Known good dock flex still does not show anything in iTunes.

I have been working off a DCPS and realize now that I forgot to mention that it draws about .2A for a bout 10 seconds, then starts constantly varying the draw between that .2A and about 1A and everywhere in between and never stops. Just keeps bouncing around. Perhaps its boot looping?

 

[jessa]

That sounds like booting---do you have a known good display on the phone?