Suggestions on a good approach to fault finding a dead iPhone PCB
I know fault finding no power faults is a well trodden path, and the cause can be wide and varied. However, after recently fault finding several dead iphone pcbs I want to improve my approach from my current almost random plan of attack. I’ve done a lot of searching online and on this forum as I thought I’d find a best practice method, I appreciate that there is no holy grail approach but I thought I could gather a few ideas together which may be interesting and may help others that stumble across this thread. I know there’s probably a sensible place to stop and give up, but lets say in a situation where there was critical data required from the device and time, effort and replacement parts weren’t an issue, what are peoples thoughts on the best logical approach (assuming there’s no background on what’s wrong with the device).
My current approach:-
- Remove all shields and visually inspect the PCB.
- Connect to DCPS and fault find any shorts/partial shorts that are getting hot. If there’s no short or partial short is not getting hot (say less than 300ma) then continue with step 3.
- Check PP_VCC_Main & PP1V8_ALWAYS for voltage
- Check all main power rails individually and then all sub power rails for a short.
- Check diode reading of each power rail to a known good board (if available)
- Replace Tigris (this is where it becomes random)
- Replace Tristar
- Replace Baseband
Hopefully I can develop this into a good logical approach.
Thanks for reading and thoughts!