My 4S needed a power button cable. When I removed the earpiece speaker it was almost impossible not to tear the foam seal that attached the speaker to the ribbon cable. It was stuck on the ribbon and the seal tore easily. After I reassembled the phone the earpiece speaker is very faint. I believe that the ribbon acts as a sound board for the speaker so if the foam seal is damaged, as mine is, it will significantly reduce the speaker volume. I ordered a new speaker, I will post my results.

The phone would not boot! The battery was at about 15% before I started. After I replaced the display the phone would not boot. After disassembly & reassembly numerous times looking for a problem, even reinstalling the old display-no boot. In final desperation I plugged in the charger-the phone booted! Apparently if the battery voltage gets too low it will not start the phone after the battery has been disconnected or the phone disassembled.

I don’t know if this problem has an explanation or was unique to my repair.