Apple will repair faulty power buttons on the iPhone 5 for free.
https://ssl.apple.com/support/iphone5-sleepwakebutton/
I haven't been able to determine if this also covers the volume down button issue. Seems like it should though considering it's all on the same ribbon cable.
https://ssl.apple.com/support/iphone5-sleepwakebutton/
I haven't been able to determine if this also covers the volume down button issue. Seems like it should though considering it's all on the same ribbon cable.