Really annoying intermittent lag after a very technical repair/project
I hope you’re all well. I have an issue that I think is very very likely self caused but very annoying and frustrating at the same time. I am familiar with working on iphones and I have a few iphones sat in the drawer that I’ve never been able to diagnose. As a project I decided to take a 6s that was dead/stuck at 0.02 amps on DCPS, I’d tried everything I possibly could to get this phone working but it was beyond me. I’ve basically swapped the CPU+Baseband & eeprom+Nand to a board that to my knowledge worked fine besides being iCloud locked. I say to my knowledge as I never experienced any issue when testing it, but then again it has worked fine after swapping out the CPU etc but I have an intermittent issue with lag, possibly now a permanent issue. I know these types of repairs are risky and can potentially bring with them all sorts of issues and it’s far from easy to see what could have happened but as mentioned this is more of a project and I’d just love to crack this issue.
So after the board swap, everything seemed to wrok fine for a few hours, I was able to restore and activate, I tested almost everything and it was fully functional, I used it myself for a couple of hours. After a few hours it started to have a general lag/delay when anything is clicked. I tried a restart and found it took a long time to boot (over a minute) and the lag continued. I tried charging and looking over the board etc and decided to reflow the CPU, miraculously it started working fine again, boots much quicker, everything worked, rebooted several times. It worked for about a day and then back to the same issue, long time to boot and a lag. After not being able to find an issue I wondered if reflowing the CPU actually did anything or if it was just heating the board that worked. I heated the board to around 140 degrees, so not enough to actually melt any solder, and again this solved the issue, temporarily. I’ve tried to whittle down exactly what area needs heat to resolve this but I can’t seem to put my finger on it and it now seems that heating the board doesn’t do the trick anymore (it did work 4 or 5 times). The interesting thing is when I boot using DCPS it has the same issue but only draws between 0.2 and 0.3 amps during boot up, it never goes above this. Normally I’d see a fluctuation on DCPS and spikes to around 0.8/0.9amps. This left me scratching my head and I replaced Tristar/U2 charging IC but this has made no difference. I’ve removed and reballed the CPU again but still have the same issue. The only other really weird thing about it is the phone will power instantly if I just tap the power button i.e I don’t need to hold for 2 seconds for it to boot, it will literally boot if I just tap the button.
I’m assuming it must be either pseudo soldering caused by too much heat on the board or an internal board fault. Could it possibly be a bad coil or something? I know most people would just give up at this point but I’d love to solve this annoying issue, I’m now at the point where I think the only way to solve it is to move everything to another donor board… but I’d like to exhaust other options first and I’m just struggling to know where to look.
Eternally greatfull for all opinions as usual!