Chosen Solution
Hi there, Currently i’m having random cellular drops at least multiple times per minute on my 6s. I’m on ios 12.1.2 (16C104), but also had the problems on 12.1.1. The problem started after working a day in the cold. When I put my phone on the charger afterwards, I mentioned the problem after an hour of charging. The phone was empty when I started charging it. If I boot my 6s, the phone asks for my SIM code but the screen immediately disappears for multiple times. After multiple minutes I can finally enter the code and it keeps searching for literally minutes or hours for my cellular network. After it has finally connected to my cellular network it starts dropping multiple times per minute. Calling over WiFi works fine, however only after the phone has established an LTE/3G connections at least once after booting. Good to know: I have another iPhone 6s with a dead logic board, swapping out parts is an option for me, but first I want to try all other options available.Imei is available in Settings -> Info, however not when calling *#06#Sim apps is appearing and disappearing in Settings -> CellularSim pincode is appearing and disappearing in Setting -> CellularPhone is A1688 model (Netherlands / EU).LOG FILE AVAILABLE: https://kramer.audio/iphonecellularlog.t… What I tried: my Sim card in other phones works fine, other sim cards in my phone have same issues.Full restore of ios (without restoring backup, so no network settings restored).Full restore with iMazing (rewrites baseband firmware).Problem appears little worse during charging, (drops 10x per minute instead of 7x)Connected phone to console on Mac OS, log is added, baseband probably has issues.I replaced already the lightning and headphone jack module, problem still appears. What I can try: Swapping partsReflow baseband chip? What I think is that something let loose, because if the phone works fine and I don’t move the phone it works up until 30 seconds instead of 5 seconds (but this may be just a feeling though). Does anybody know which part is most likely to be damaged? I read that the power IC’s for the iPhone 6 fail often, however this is an iPhone 6s. I also know that a lot of chips can’t be replaced without rewriting the NAND, is this the same problem with the baseband chip? I have done reballing / swapping out chips before, but I consider this as an option when no other options are left.
I don’t generally recommend reflowing as an option, the preferred method is reballing the IC. You cannot replace the baseband IC as it is code-locked to the NAND and CPU and it is not programmable. I would probe the output voltages of the Baseband PMU (U_PMU_RF) to see if any of them are erratic and possibly reball that IC as well. As you suggest, there may also be some surrounding components that have cracked solder joints or possibly even dislodged so a good visual inspection would be appropriate.
