We received an iphone 7 plus recently for no power. Our customer told us that when they connected a new battery the motherboard would smoke.
When we received the device we plugged it into our power supply and just as the client said we saw smoke coming from M2800 the trinity IC, often called the touch ic but it is actually just a cluster of coils for several different lines built into one IC. we also saw a 5 amp short on the main power line.
First off we removed the trinity IC, which is an ic that contains several coils, to find out which line was shorted. We found the short on the speaker amp line, so then we knew where to look! We flipped the board over to look around the speaker amp circuits and found a burnt out capacitor in the C3404 position.
We removed this capacitor and the short was resolved. Next we replaced the trinity IC with a new one and plugged the phone into our power supply. The short was gone so we prompted the phone to boot, the phone appeared to turn on and function normally so we unplugged it and fitted a new capacitor. We then cleaned the logic board and reassembled the device and charged it up for full testing. The device seemed to function perfectly so we returned to the customer who was very happy to have their device back fully working.
We have seen similar issues with shorts causing the trinity IC to fail but this was a first on this particular line, this is why we love board level repairs, each one is slightly different and you have to think on your toes!