Here is a summary of weird iPhone problems I've personally seen, and suspected cause: iPhone 4S Unreliable WiFi (WiFi function not available) Diagnosis: logic board fault. Potentially requires logic board re-work or replacement. Thoughts: Perhaps caused by a drop. iPhone 5 Volume Buttons Don't Function Diagnosis: logic board fault (and not the buttons or its cable). Potentially requires logic board re-work or replacement. Thoughts: misbehaving aftermarket charger put out high voltage, damaging logic board. iPhone 6 GPS doesn't work well (or at all). Diagnosis: GPS antenna needs reseating and/or replacement. I recently fixed this by merely reseating the antenna assembly. Thoughts: Perhaps caused by a drop, or just random. iPhone 6S cell service gives no signal. Diagnosis: cell circuitry dead on logic board. Potentially requires logic board re-work or replacement. Thoughts: Perhaps damaged by hard drop. iPhone 7 bad audio circuit. Diagnosis: logic board ...
Useful and Useless Ideas from Lance J.