How to Know if Your iPhone Has Circuit Damage?
Your iPhone contains complicated circuitry designed to perform the various computer-like operations you need. Consequently, these delicate electronics are susceptible to damage from various sources. A damaged circuit does not function properly again and must be repaired or replaced.
1 Restart the Device
The signs of a damaged circuit are similar to those of an iPhone suffering a harmless electronic "hiccup." You may experience unusual operational problems such as app crashes or phone freezes. Restart your iPhone by holding the "Sleep/Wake" button until the red slider appears. Slide the arrow on the slider to the right to power down. Press the "Sleep/Wake" button again to turn the phone on again. For frozen phones that do not respond to normal restart procedure, hold the "Sleep/Wake" and "Home" buttons at the same time to force a restart. If the device returns to proper operation afterward, your issues were simply glitches that the restart corrected. If your phone continues to malfunction, you are dealing with circuit damage.
2 Circuit Damage Causes
Generally speaking, circuit damage typically occurs due to some outside stimuli such as water damage or an electrical or physical shock. Apple offers an easy way to check for water damage, as a small red liquid indicator appears on the side of the phone after it gets wet. The device could have also suffered a lightning strike while charging, or experienced a fall that may have jostled the internal components. If you suspect circuit damage, visit your local Apple Genius Bar for help (see Resources).